Showing papers in "Acta biologica et medica Germanica in 1982"

The insulin-releasing activity of the tropical plant momordica charantia.

Abstract: An aqueous extract from the unripe fruits of the tropical plant Momordica charantia was found to be a potent stimulator of insulin release from beta-cell-rich pancreatic islets isolated from obese-hyperglycemic mice. The stimulation of insulin release was partially reversible. It differed from that of D-glucose and other commonly employed insulin secretagogues in not being suppressed by L-epinephrine and in even being potentiated by the removal of Ca2+. This anomalous behaviour was not associated with general effects on the metabolism of the beta-cells as indicated by an unaltered oxidation of D-glucose. Studies of 45Ca fluxes suggest that the insulin-releasing action is the result of perturbations of membrane functions. In support for the idea of direct effects on membrane lipids, the action of the extract was found to mimic that of saponin in inhibiting the Ca2+/H+ exchange mediated by the ionophore A23187 in isolated chromaffin granules and release Ca2+ from preloaded liposomes.

Inhibition of hepatocytic protein degradation by inducers of autophagosome accumulation.

Abstract: Out of nine compounds known to induce accumulation of autophagosomes, seven were found to inhibit degradation of endogenous protein and all of them to inhibit degradation of an exogenous protein (asialofetuin) in isolated rat hepatocytes. On the basis of these findings we propose two possible common mechanisms by which the drugs may cause autophagosome accumulation: 1) The inhibition of protein degradation may result in a decrease in the intracellular amino acid levels, a change which in turn serves as a stimulus for increased autophagic sequestration. 2) Disturbance of the function of the lysosomes may reduce their ability to fuse with newly formed autophagosomes, thereby causing accumulation of the latter.

Low dose streptozotocin diabetes after partial pancreatectomy in dogs. Histological findings in a new type of experimental diabetes.

Abstract: Permanent diabetes was produced in 16 out of 55 dogs by partial pancreatectomy (77% of the calculated organ weight) and simultaneous infusion of 2 mg/kg streptozotocin into the superior pancreaticoduodenal artery. The animals exhibited hyperglycemia, absolute lack of endogenous B-cell function, and ketosis, but no exocrine pancreatic insufficiency. 21 animals needed up to 7 additional subsequent intravenous streptozotocin injections (15 mg/kg each at intervals of 3 days). In 18 animals the procedure failed to render them diabetic; they died mainly from toxic effects of the drug. There were severe pathohistological changes in all streptozotocin-treated animals. Besides the well known alterations of the islets of Langerhans, lymphocytic inflammations were found in numerous organs including the exocrine pancreas. In most cases they were combined with degenerative changes of the organ parenchyma, particularly in kidney and liver. These findings were not correlated to the sex of the animals, to the occurrence and severity if diabetes, to the time of survival, or to the streptozotocin dose applied. But they were obviously related to the clinical picture existing besides diabetes. It is concluded that the model of experimental diabetes presented might be useful in a carnivorous big animal species but that toxic streptozotocin effects are to be expected when the dose administered exceeds 2 mg/kg.

Properties of thermitase, a thermostable serine protease from Thermoactinomyces vulgaris.

Abstract: Some structural and catalytic properties of the extracellular serine protease thermitase, purified by chromatography on porous glass, are reported. The crystal data and the high elastinolytic action point to possible relationship of thermitase with pancreatic elastase. Subsite-mapping studies clearly indicate, however, that thermitase contains an extended binding region and is closely related to the subtilisin group. The enzyme shows maximal stability between pH 6.0 and 7.5 and maximal activity between pH 7.5 and 9.5. The larger the substrate, the higher is its temperature optimum (60 degrees C for esterolysis, 85 degrees C for proteinolysis). The stability of thermitase is significantly improved by acetates and chlorides at 1 M concentration. Besides its high hydrolytic action on soluble proteins thermitase is capable for efficient degradation of the insoluble proteins elastin and collagen.

Effect of substance P on the retention of a brightness discrimination task in rats.

Abstract: The effect of substance P (SP) on acquisition and retention of a footshock-motivated brightness discrimination was investigated in rats, 250 micrograms SP/kg were injected intraperitoneally either 30 min before or immediately after the training session. Acquisition of the brightness discrimination was not affected by SP administered 30 min before training. However, both the pre-training and post-training injections of SP resulted in a significant improvement of retention tested 24 h after training. The effect of SP on memory consolidation is discussed.

Effect of linoleic acid-rich diet on blood pressure, lipids, catecholamines, and dopamine -beta-hydroxylase in spontaneously hypertensive rats.

Abstract: Spontaneously hypertensive rats (SHR) and normotensive Wistar rats were fed a linoleic acid-rich (LAR) and -deficient (LAD) diet for 22 weeks, respectively. Although linoleic acid (LA) and arachidonic acid (AA) in serum and liver triglycerides markedly increased after a LAR diet, LA was significantly lower and AA was higher in SHR when compared to normotensive control rats. Thus, the percentage of both fatty acids remained different like in animals fed a commercial diet. On the contrary, in SHR and normotensive rats fed a LAD diet no differences in the LA and AA content could be found between the groups. In these rats, however, n-3 fatty acids (eicosapentaenoic and docosahexaenoic acids) in serum triglycerides were increased. Blood pressure, serum triglycerides and total cholesterol appeared unchanged, whereas HDL-cholesterol was increased after a LAR diet. Dopamine, adrenaline and noradrenaline content as well as dopamine-beta-hydroxylase activity were augmented in adrenal glands of SHR fed a LAR diet. In spite of distinct biochemical alterations the genetically determined hypertension in rats could not be influenced by a long-lasting diet containing a high amount of LA which has been proved to be effective on lowering blood pressure in other hypertensive rat models.

Rodent islet cell antigens recognized by antibodies in sera from diabetic patients.

Abstract: Rat islets, rat insulinoma cells and islets from three different mouse strains were labelled with 35S-cysteine and/or 35S-methionine. Detergent lysates of the cells were subjected to immunoprecipitation with sera from 5 newly diagnosed diabetic children and 5 control sera. The immunoprecipitates were analysed by sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis followed by autoradiography. One of the sera immunoprecipitated a protein of Mr 64K from lysates of rat islets, rat insulinoma cells, A. TH and NMRI but not CBA/H mouse islets. This protein was not consistently immunoprecipitated by the other diabetic sera, however, it was never found with control sera nor was it detected in rodent lymphocytes. Some proteins of lower molecular weight (59K, 57K, 40K, 29K) were specifically immunoprecipitated by one or more diabetic sera from some of the rodent islet cell preparations. It is concluded that rodent islet cells contain a protein of Mr 64K which may be antigenically related to a 64K protein previously detected in immunoprecipitates of human islet cells with the same diabetic sera. The variable results with rat and mouse islet cell material suggest that the level of cross-reactivity is low. Further studies are needed to clarify whether the lower molecular components detected in some immunoprecipitates represent other antigenic determinants or degradation products of the 64K protein.

The major histocompatibility complex and insulin-dependent diabetes in BB rats.

Abstract: The partially inbred strain of BB-Wistar rats showed a varying incidence of the insulin-dependent diabetes-like syndrome. The serological typing of a large sample of BB rats verified the homozygosity for the RTlu haplotype, whereas its parental non-inbred Wistar stock segregated for RTlu and RTla haplotypes. The histogenetical typing of BB rats by skin grafting showed a significantly prolonged rejection of grafts from RTla donors unusual in other RTlu recipients. The presumption of some recombinational or mutational events in the RTl haplotype of BB rats was not verified by the simple F1 skin grafting test from LEW.1U/RTlu standard/donors to F1/LEW X BB/recipients. Skin grafts survived permanently. When trying to get a clear-cut answer whether the RTlu haplotype is associated with the spontaneous occurrence of diabetes in F2/LEW X BB/ X /LEW X BB/hybrids, only 7.4% of RTlu homozygotes were found among 359 weaned animals. Moreover, the partial strain of BB rats became extinct with the F1 generation mainly due to an infection by the mycoplasma. A new sample of outbred BB rats with a low incidence of spontaneous diabetes was found as homogeneous for the RTlu haplotype, too. Preliminary results of typing these rats for the secondary antibody response to pig insulin indicate the low responsiveness contrary to the results given earlier for the RTlu typing strains as high responders. All these results support the idea that the RTlu haplotype of the BB rats might be a variant carrying some mutational change(s) at the RTl.B region.

Inhibitory effects of hypoxia on dopamine release.

Abstract: Behavioral and neurochemical results refer to an impairment of the dopaminergic system produced by hypoxia. On that account we determined the chemically (K+, amphetamine) and electrically stimulated release of dopamine from rat striatum slices which were preloaded with labeled dopamine following the animals' exposure to hypobaric hypoxia. The effect of hypoxia consists in a marked inhibition of dopamine release depending both on the degree of hypoxia and on the kind of stimuli used. Dopamine release inhibition reflects not only the direct effect of hypoxia, which seems to be connected especially with the vesicular compartment, but also adaption and restitution processes. Regarding the effects on rats at the age of two weeks the resistance of young animals against hypoxia may be founded also upon missing vesicular mechanisms of distinct vulnerability.

Effects of 3-isobutyl-1-methylxanthine on secretory response, cAMP accumulation and DNA synthesis of islets from postnatal and adult Wistar rats.

Abstract: A possible role for cyclic adenosine-3'-5'-monophosphate (cAMP) in islet cell replication was examined in collagenase-isolated pancreatic islets from Wistar rats of different age and different metabolic state (non-pregnant, pregnant, days 15.5-17.5). Islets obtained from pregnant rats released significantly more insulin in response to 10 mmol/l glucose (culture for 24 h) and their DNA synthesis (incorporation of [3H]thymidine into islet DNA) was doubled compared to islets from non-pregnant controls. Islets obtained from 4-6 days old rats showed a maximal stimulation of DNA synthesis after exposure to 0.1 mmol/l IBMX (3-isobutyl-1-methylxanthine) whereas the cAMP accumulation and the insulin biosynthesis measured in a subsequent short-term incubation were dose-dependent stimulated up to 1.0 mmol/l IBMX. In islets of 12 days old rats or 3 months old rats, however, IBMX did not stimulate DNA synthesis or insulin release measured during culture, although the cAMP content per islet was significantly enhanced after culture in the presence of IBMX.

Acetylcholine concentrations in the developing brain appear to affect emotionality and mental capacity in later life.

Abstract: A decrease of the acetylcholine concentration in the brain of infantile rats was induced by maternal deprivation in neonatal life, which was associated with emotional and mental ill-effects in later life The decreased acetylcholine concentration in the infantile brain as well as the permanent emotional and mental ill-effects, which were produced by neonatal deprivation, could be prevented by neonatal administration of the acetylcholinesterase inhibitor pyridostigmine These findings suggest that acetylcholine can be considered as an important, environment-dependent local organizer of the brain

The effect of piracetam on posthypoxic dopamine release inhibition.

Abstract: Subsequently to a hypoxic exposure of adult rats the stimulus induced release of dopamine from striatum slices in inhibited for several days. Depending on the treatment with piracetam the restitution of this inhibition is accelerated manifold, though piracetam does not prevent the acute effect of hypoxia on dopamine release. The particular hypoxia related vulnerability of the potassium evoked dopamine release and the time course of piracetam effect obviously point to drug induced anabolic processes rebuilding vesicle storage sites.

Receptor Mediated Endocytosis of Hemoglobin-haptoglobin, Galactosylated Serum-albumin and Polymeric Iga By the Liver

Abstract: Labelled hemoglobin-haptoglobin (ham-hap), galactosylated serum albumin (gal-SA) and polymeric immunoglobulin A (p IgA) were injected intravenously to rats or mice. The labels disappeared from the plasma with a half-time of about 5 min and were almost entirely found associated with the liver where degradation products progressively appear. The uptake of hem-hap and gal-SA are partially saturable as a function of the plasmatic concentration and the uptake of gal-SA can be completely inhibited by the simultaneous injection of asialofetuin. About 45 min after injection to rats, labelled material appears in the bile in amounts corresponding to 3.9% of the injected dose (hem-hap), 2.8% (gal-SA) and 60.1% (p IgA). The molecular weight of the labelled material transferred into the bile has been characterized: it consists almost entirely of intact IgA and for about 60% of intact hem-hap and gal-SA. Cell fractionation experiments indicate that 4 min after injection, the label is associated with components which equilibrate around a density of 1.13 g/cm3 and which dissociate from marker enzymes of Golgi complex, plasma membrane and lysosomes. Longer times after injection (from 20 min for hem-hap and gal-SA to 1 h for p IgA) labelled material appears, within lysosomes. To explain all these data, we suggest that after binding to plasma membrane receptors, the ligands are rapidly interiorized into pinocytic vesicles which fuse with lysosomes. Most of the hem-hap and gal-SA molecules but only part of p IgA would be released and subsequently digested; these vesicles would dissociate from lysosomes and fuse with the biliary membrane where the molecules still bound to the membrane of the vesicles would be detached and excreted into the bile.

Behaviour-dependent changes of visually evoked potentials and their correlation to the respiration rate in freely moving rats.

Abstract: The variability of visually evoked potentials (VEP) during spontaneous changes of behavioural activity was investigated in freely moving rats with electrodes in the visual and frontal cortex, olfactory bulb and other brain structures. Averaged VEP were recorded and compared during periods of characteristic behaviour types like drowsiness, relaxed wakefulness, attentiveness, grooming and exploratory behaviour. These behavioural patterns, which are clearly distinguishable by observation, were characterized by a certain degree of visually evoked afterdischarges, recorded movements, EEG-patterns and mean respiration rate. The evaluation of early components of the VEP from single recorded samples and of the correspondent momentary respiration rate (respiration intervals) revealed strongly negative correlations. In general, the increasing behavioural activity is characterized by a decrease in the amplitudes of VEP-components, inversely correlated to the log of momentary respiration rate. During drowsiness and enhanced attentiveness, certain components are increased. During strong movements and distraction of attention (e.g. intensive scratching and licking) the VEP-components were decreased stronger. The negative complex around 62 ms increased during certain forms of behavioural activation and locomotion. The VEP-component N31, the respiration rate, and the quotient N31: N61 were found suitable parameters to characterize certain types of behaviour in comparison to relaxed wakefulness.

A quick test for the simultaneous determination of intactness and concentration of spermatozoa.

Abstract: The fluorescence of ethidium bromide bound to the DNA of bull spermatozoa can be used for the estimation of intactness and concentration of spermatozoa of washed sperm samples. For the full permeability of the spermatozoal membrane for ethidium bromide digitonin is used in a concentration of 50 micrograms/ml. The fluorescence signals before and after digitonin treatment reflect the portion of cells with intact cellular membrane in the sample. The signal after addition of digitonin correlates to a high degree with the sperm concentration. The method exhibits a sufficient accuracy for the estimation of sperm quality. That applies for the reproducibility with individual ejaculates as well as for the correlation to other methods determining the intactness and sperm concentration. This simple single-step technique requires only about 2 X 10(7) spermatozoa corresponding to 10 to 20 microliters of an average bull ejaculate.

Expression of the insulin gene: regulation by glucose, hydrocortisone and growth hormone in mouse pancreatic islets in organ culture.

Abstract: Isolated pancreatic islets from mouse were maintained in organ culture at either 3.3 mM glucose or 20 mM glucose to study the effect of glucose on the level of preproinsulin mRNA. In islets cultured at 20 mM glucose for up to 7 days, the level of preproinsulin mRNA remained constant, but in islets kept at 3.3 mM glucose the preproinsulin mRNA level decreased within 24 h to one tenth of the level in islets maintained at 20 mM glucose. The level of preproinsulin mRNA could, however, be completely restored by subsequent incubation at 20 mM glucose for 3 days. These results suggest that glucose has a direct effect on the level of preproinsulin mRNA in pancreatic islets. The biosynthesis of proinsulin was correlated to the variation in the level of the preproinsulin mRNA, suggesting that the rate of biosynthesis of proinsulin is limited by the level of the preproinsulin mRNA. Initial experiments with hydrocortisone and human growth hormone, both known to enhance insulin release from islets in organ culture, showed that the level of preproinsulin mRNA was increased in islets cultured in the presence of these hormones.

Effect of dietary trans fatty acids on cholinesterase and monoamine oxidase activities in different organs of rats.

Abstract: The effect of trans fatty acids and essential fatty acid deficiency upon the activities of cholinesterase and monoamine oxidase in livers, hearts, brains and lungs of rats was studied. This study was performed using three groups of male albino rats. Two out of these three groups were fed essential fatty acid low diets containing 10% hydrogenated coconut oil (HCNO) or margarine stock (MS, partially hydrogenated soybean oil) while the third group was fed an adequate supply of essential fatty acids through a diet containing 10% corn oil (CO). In the group of rats fed HCNO the activities of cholinesterase and monoamine oxidase in their livers, hearts, brains and lungs were not significantly different from those of the control group fed CO. In the group of rats fed MS, the activity of cholinesterase was significantly decreased in the livers, hearts and brains, but not affected in the lungs, while the activity of monoamine oxidase was significantly decreased in the livers and hearts but not affected in the brains and lungs as compared to the control group fed CO. The levels of serum total lipids, total cholesterol and triglycerides were elevated in both groups of rats fed HCNO or MS than in the group fed CO, but this elevation was more highly significant in the group fed MS than in the group fed HCNO.

Some aspects of plasma-protein metabolism as compared with intracellular protein breakdown

Abstract: Many plasma proteins are cleared according to first-order kinetics. Half-lives of individual plasma proteins are widely different, just like those of intracellular proteins. Plasma proteins with molecular weights up to about 50000 are often mainly cleared by glomerular filtration, especially if the protein has a high isoelectric point. An other important clearance mechanism is endocytosis. Fluid endocytosis might contribute significantly to the catabolism of plasma proteins with long-lives like serum albumin. Adsorptive endocytosis is responsible for the rapid clearance of complexes of some plasma proteins with other molecules, like antigen-antibody complexes. Other plasma proteins like certain glycoproteins and lipoproteins are bound to be specific receptors on the surface of endocytosing cells without previous complex formation. Experiments with sucrose-containing labels suggest that certain tissues are specifically involved in endocytosis of some plasma proteins. If endocytosis and renal filtration constitute the main mechanisms for the clearance of plasma proteins, one cannot expect extensive homologies between this process and catabolism of intracellular proteins.

The toxic A-chain of mistletoe lectin I: isolation and its effect on cell-free protein synthesis.

Abstract: The reduction of Sepharose bound mistletoe lectin I (ML I) is a convenient method for preparing A- and B-chains under mild conditions. The B-chain represents the D-galactose binding moiety. The A-chain shows a significant dose-dependent inhibition of protein synthesis in cell-free systems from rat liver and rabbit reticulocytes, while pure B-chain preparations do not affect ribosomal translation processes.

Diabetes mellitus in mice induced by multiple subdiabetogenic doses of streptozotocin: age and sex dependence.

Abstract: In order to investigate whether age and sex have an influence on induction and development of diabetes, male and female C57Bl/KsJ mice of different ages were treated with subdiabetogenic injections of streptozotocin for five consecutive days. After a long period of observation all treated animals became diabetic. Male mice showed higher plasma glucose values than female animals suggesting a sex dependence. In the first phase of diabetes development the hyperglycemic response was dependent on the age of the mice. Animals treated during puberty, both male and female developed a more rapid onset of hyperglycemia and a more severe diabetes than the other age groups. The increased plasma glucose levels were accompanied in mice treated after and during puberty by an inflammatory lesion of the endocrine pancreas.

The mechanism of sulfonylurea stimulation of insulin release.

Abstract: The mechanisms for sulfonylurea stimulation of insulin release were explored by studying how these compounds interacted with beta-cell-rich pancreatic islets isolated from ob/ob-mice. Although sulfonylureas from the "second generation" were taken up to a greater extent, there was no direct correlation between the binding to the islets and the stimulation of insulin release. Drugs, which are known to augment the hypoglycemic action of the sulfonylureas, displaced these compounds from serum albumin to the islets. Sulfonylurea binding to the beta-cells is supposed to result from a hydrophobic interaction of the drug with the beta-cell surface counteracted by electrostatic repulsion from fixed negative charges at the cell surface. Like glucose, the sulfonylureas stimulate insulin release by promoting the Ca2+ influx into the beta-cells. The enhanced Ca2+ influx cannot be accounted for by Ca2+-ionophoretic activity but is secondary to a depolarisation of the beta-cells by a mechanism which may involve a reaction with thiol groups in the plasma membrane.

Inhibition of cysteine proteinase activity by Z-Phe-Phe-diazomethane and of aspartic proteinase activity by pepstatin in different organs from some animals and isolated cells from rat liver.

Abstract: Two methods have been developed to discriminate simultaneously between the main part of cysteine proteinase activity (cathepsin L) and all aspartic proteinase activity (mainly cathepsin D) in rat organs, using Z-Phe-Phe-CHN2 which at 5 mumol/l completely inhibits cathepsin L from rat liver and, on the other hand, pepstatin which at 0.5 mumol/l completely inhibits cathepsin D. Substrates are double-labeled cytosol proteins from rat liver at pH 3.0 or azocasein in 3 mol/l urea at pH 5.0. Several organs from rat, pigeon, frog and carp have been investigated using these methods. Especially kidneys from rat, frog and carp contain a high Z-Phe-Phe-CHN2 inhibited activity. Investigating the different liver cell types we could confirm earlier findings that Kupffer cells and endothelial cells contain more pepstatin inhibited activity than parenchymal cells.

Mobility and clusterlike organization of liposomal cytochrome P-450 LM2: saturation transfer EPR studies.

Abstract: Rotational diffusion of the electrophoretically homogenenous isozyme cytochrome P-450 LM2 from rabbit liver microsomes has been studied in buffer solution and in phospholipid vesicles by means of saturation transfer EPR spectroscopy. Sulfhydryl groups of the enzyme were selectively modified using a maleimide spin label. The effective rotational correlation time of 220 ns for the rotation of cytochrome P-450 in buffer solution is consistent with the fact that the purified free enzyme occurs as an oligomeric (6-8 monomers) aggregate. Further, the clusters rotate almost isotropically and therefore are in a first approximation spherically shaped. The effective correlation time of about 180 microseconds observed strong immobilization thus evidencing protein aggregation within the membrane. The anisotropic character of the spectra indicates a nonspherical shape and/or anisotropic rotational motion of the cluster. The results are compared with corresponding data from cytochrome P-450 in microsomal form.

Role of the hydrophobic tail of cytochrome b5 in the interaction with cytochrome P-450 LM2.

Abstract: The interaction of cytochrome P-450 LM2 with cytochrome b5 is accompanied by a high spin shift in P-450 LM2 and the improvement of a second derivative spectra in the near ultraviolet region. After incorporation into phospholipid vesicles the interaction between P-450 LM2 and b5 is increased according to a decrease of the apparent binding constant. The involvement of a tryptophanyl residue in the interaction will be discussed. Contrary the tryptic fragment of cytochrome b5 which lacks the membrane binding tail does not show an interaction with P-450 LM2 either in the absence or presence of phospholipids.

Structural transitions of the erythrocyte membrane: an ESR approach.

Abstract: The effect of temperature and ionic strength on the ESR spectrum of the fatty acid spin label I (10,3) in membranes of freshly drawn human red blood cells has been investigated. The results suggest that the microviscosity of the membrane is not strongly influenced by the ionic strength. Discontinuities at various temperatures could be observed, which disappear after cholesterol treatment. The possible role of membrane lipids and proteins on the thermotropic membrane behaviour observed is discussed. It is assumed that the spectra are averaged signals from different regions of the membrane.

Investigations on the substrate specificity of thermitase, a thermostable serine-protease from Thermoactinomyces vulgaris.

Abstract: The kinetic parameters Km and kcat and the proteolytic coefficients kcat/Km for the hydrolysis of eighteen Z(benzyloxycarbonyl)-dipeptide methyl esters with variation of the residues in P1 and P2 position catalyzed by thermitase at pH 8 and 55 degrees C are reported. The results indicate that an integral part of both subsites, S1 and S2, are hydrophobic areas and that a mutual interaction between the side chains of P1 and P2 for optimal hydrolyisis does exist. Furthermore, the importance of the P2 for the peptidolytic activity of thermitase was shown using N-acylated oligo-alanine peptides and their p-nitroanilides. In all cases dialanine or alanine p-nitroanilide are the main products.

A new procedure for the purification of proteinase B from baker's yeast and interaction of the purified enzyme with a specific inhibitor.

Abstract: Proteinase B from baker's yeast was purified to homogeneity by applying affinity chromatography with D,L-tyrosine ethyl ester as ligand. The molecular parameters of the product are similar to those reported formerly by other groups. A different form of proteinase B is isolated if affinity chromatography is replaced by CM-cellulose chromatography and gel filtration. In this case a peptide tightly associated with the enzyme was found to occur. This could be identified as an inhibitor fragment produced by limited proteolysis of a proteinase B bound inhibitor induced by proteinase A.