Showing papers by "Public Health Research Institute published in 1974"

Bile acid biosynthesis. Pathways and regulation.

Abstract: This review summarizes certain biochemical aspects of bile acid biosynthesis. It is pointed out that our knowledge of the biosynthetic pathway is still incomplete. The significance of alternate pathways in the biosynthesis of the primary bile acids, cholic acid, and chenodeoxycholic acid remains to be evaluated, and the details of the side chain degradation of the C27 bile alcohols are not fully understood. The rate of bile acid synthesis from cholesterol is regulated by the enzyme cholesterol 7o~-hydroxylase. H M G CoA reductase (3-hydroxy-3methylglutaryl coenzyme A reductase), the rate-limiting enzyme of cholesterol synthesis, may play an important role in the regulatory process by controlling the quantity of newly synthesized cholesterol available for bile acid production. Biliary bile acid composition appears to depend, in part, upon the activity of two enzymes: a 12c~-hydroxylase, and a 26-hydroxylase acting upon either 7c~-hydroxycholest-4-en-3-one or 5B-cholestane-3~, 7~diol. The regulation of sterol/bile acid metabolism is defective in cerebrotendinous xanthomatosis (CTX), a rare, familial sterol storage disease. In CTX the activities of the rate-limiting enzymes of sterol/bile acid biosynthesis are abnormally elevated, yet bile acid excretion is low because of incomplete degrada-

Regulation of Bile Acid Synthesis

Abstract: Bile acids formed from cholesterol in the liver are defined as “primary” bile acids. In man, these are chenodeoxycholic acid and cholic acid. Following conjugation with glycine or taurine the bile acids are secreted into the bile and stored in the gallbladder. After participating in the intestinal digestive process the bile acids are reabsorbed from the ileum, and return to the liver via the portal system. This enterohepatic circulation preserves the bile acids for repeated utilization.

Regulation of the β-Glucoside System in Escherchia coli K-12

Abstract: In Escherichia coli wild-type cells, a mutation at the beta-glucoside regulatory gene (bglR(+) to bglR(-)) leads to simultaneous expression of inducible phospho-beta-glucosidase B (bglB(+)) and a beta-glucoside-specific species of enzyme II (beta-glucoside transport I [bglC(+)]); an additional mutation (bglS(+) to bglS4) allows these enzymes to be formed constitutively. The bgl alleles have been mapped in the following order: pyrE, bglA, bglB, bglS, bglR, bglC, ilvD. The back mutation in the regulatory allele (bglR(-) to bglR(+)) caused the cessation of the expression of the bglB(+), bglS(+) or bglS4, bglC(+) alleles. However, a mutation in a strain with bglB(+), bglS4, bglR8, bglC(+) alleles, at the ini site that lies between the bglS4 and the bglR8 allele, allowed the expression of the bglS4 and bglB(+) alleles, but showed no affect on the expression of the bglC(+) allele. It is suggested that the ini mutation possesses a promotor-type function that in the absence of regulatory allele function (bglR8) renews the functioning of only the bglS4 and bglB(+) alleles. The complementation studies have shown that the bglB(+), bglS(+) or bglS4, bglC(+) alleles are expressed only in cis to the bglR(-) allele. In the constitutive strain (bglB(+), bglS4, bglR(-), bglC(+)), the expressed bglS4 allele formed a soluble product that acts in trans over the bglB(+) and bglC(+) alleles and that appears effective only when the bglB(+) and the bglC(+) alleles are expressed in cis to the bglR(-) allele. It thus showed that the constitutive biosynthesis of phospho-beta-glucosidase B and beta-glucoside transport I is under positive control. Since the regulatory allele bglR(-) lies between the bglS4 and the blgC(+) alleles, and acts in cis, it appears that the mutation (bglR(+) to bglR(-)) allows the initiation of transcription in one direction to express the bglS4, bglB(+) alleles and in the other to express the bglC(+) allele. The structural genes bglB and bglC lie adjacent to the regulatory genes bglR and bglS, and the structural genes are coordinately controlled by the regulatory genes. It is, therefore, proposed that the bglB, bglS, bglR, bglC genes form a bgl operon.

Genetic Characterization of Recombination-Deficient Mutants of Bacillus subtilis

Abstract: Recombination-deficient (rec), radiation-sensitive mutations in Bacillus subtilis are grouped in at least seven distinct loci. Map positions are determined for six of these loci.

Effect of dietary chenodeoxycholic acid and lithocholic acid in the rabbit.

Abstract: The feeding of chenodeoxycholic acid or lithocholic acid (0.05 or 0.5% of the diet) to rabbits produced cirrhotic and necrotic changes in the liver, accompanied by an increase of secondary bile acids in bile. Animals fed 0.05% lithocholic acid, 0.05% or 0.5% chenodeoxycholic acid, but not those receiving 0.5% lithocholic acid were able to survive for a period of 21 days. The most severe cirrhotic and necrotic changes were observed in the rabbits fed either 0.5% lithocholic acid or 0.5% chenodeoxycholic acid for 6 days or longer. Liver damage appeared to correlate with bile composition. The pathologic involvement was greatest whenever the percentage of lithocholic acid in the bile exceeded 15%. It is concluded that chenodeoxycholic acid (which is not a major constituent of rabbit bile) exerts its hepatotoxic effects largely because it is converted to lithocholic acid by the intestinal bacterial flora.

Genetic control of chromosomal and plasmid recombination in Staphylococcus aureus.

Abstract: Recombination-deficient mutants of Staphylococcus aureus have been isolated and found to have properties similar to those of recombination-deficient Escherichia coli . In addition, one Rec - mutant was found to be defective in the restriction and modification of DNA. There is a marked reduction (∼ 10 4 -fold) in recombination between penicillinase plasmids in the Rec - mutants suggesting that these elements do not encode an efficient recombination system. There is, however, a demonstrable residuum of interplasmid recombination; evidence is lacking on whether this residuum is a plasmid or host function. In the absence of the generalized host recombination system it has been possible to demonstrate that interplasmid recombination occurs during vegetative bacteriophage growth and is presumably mediated by a phage-determined recombination system.

Effects of deletions on cotransduction linkage in Salmonella typhimurium: Evidence that bacterial chromosome deletions affect the formation of transducing DNA fragments

Abstract: The effect of nearby deletions on linkage between markers (all located on the same side of the deletion) was studied in two regions of the Salmonella typhimurium chromosome by bacteriophage P22-mediated transductions. A number of deletions significantly altered the frequency with which pairs of markers were jointly transduced. Since, in some cases, significant alterations in cotransduction linkage were observed when the same deletion was present in both donor and recipient, all such effects could not be ascribed to lack of homology caused by the deletion. In one case a significantly altered cotransduction frequency was noted when a deletion was located beyond the chromosomal region included on the selected transducing DNA fragments. This was observed when the deletion was present in both donor and recipient or in the donor alone but not when the deletion was present only in the recipient. These experiments indicate that some deletions alter cotransduction linkages because they affect the formation of the transducing particles, presumably by altering the proportion of transducing particles which carry both markers or by altering the position of the markers with respect to the ends of the transducing DNA fragments.

Effect of dietary bile acids, cholesterol, and β-sitosterol upon formation of coprostanol and 7-dehydroxylation of bile acids by rat

Abstract: During studies of sterol metabolism in the rat, the fecal neutral sterol fraction was analyzed by a combination of thin layer chromatography and gas liquid chromatography. On a stock diet of rat chow supplemented with 5% corn oil, the rats excreted 14.5 mg/day of total neutral sterols. Coprostanol comprised 35% (5 mg/day) of this fraction. When the diet was supplemented with 0.5% sodium taurochenodeoxycholate, the amount of coprostanol in the feces remained the same as in the controls (3.2 mg/day, 32%). The addition of 0.5% sodium taurocholate to the diet resulted in a fivefold reduction of coprostanol formation (0.6 mg/day, 8%). When 1.2% cholesterol was added to the stock diet, the amount of coprostanol present in the feces decreased to an average of 11% compared to controls, but the absolute amount formed was greater (35 mg/day). On a diet enriched with 0.8% β-sitosterol, the rats, on the average, converted 23% of the cholesterol to coprostanol. Feeding diets enriched with sodium taurochenodeoxycholate and sodium taurocholate reduced the 7-dehydroxylation of primary bile acids in the feces by 28% and 42%, respectively. The conversion of primary bile acids to secondary bile acids in the feces of control, cholesterol, and β-sitosterol fed rats was the same (64%).

Studies on plasmid replication. III. Isolation and characterization of replication-defective mutants.

Abstract: Some 85 Staphylococcus aureus mutants phenotypically thermosensitive for penicillinase plasmid segregation (Seg−) have been isolated and characterized. Some of the mutations were plasmid-linked and those studied in detail were found to be defective in plasmid replication, most probably at the initiation stage. Analysis of the segregation behavior of these mutants suggested a figure of 2.7 for the average number of plasmid copies per cell in a random culture. Other mutations were host chromosome-linked and these could be divided into at least three classes on the basis of their ability to maintain plasmids of the two different incompatibility sets: some were defective for type I plasmids, some for type II, and some for both types. One host mutant, defective in segregation of type I but not type II plasmids, was defective in polymerization of both.

Functional Organization of the Neural Control of Circulation in Aplysia

Abstract: The abdominal ganglion of Aplysia provides a useful model for studying the functional organization of motor systems. Here we review studies of the neural network controlling circulation, emphasizing the organizational features it may share with other motor systems controlled by the abdominal ganglion. We identified seven motor neurons to the heart and vascular system. Motor neurons having similar motor effects (e.g. the two heart inhibitors, or the three vasoconstrictors), together with cells of unknown motor function located near them, make up distinct homogeneous cell groups. The members of each group appear to be nearly identical with respect to biophysical and neurochemical properties, size and effectiveness of synaplie inputs, and firing patterns. There are no interconnections between the members of the groups, but five interneurons innervate the homogeneous groups in various combinations, exciting some groups and inhibiting others. Two of the interneurons, Interneuron I (cell I10) and Interneuron II, are command cells which produce centrally generated motor programs in the absence of sensory feedback. Eacli command apparently codes for a specific homeostatic function, such as increased cardiac output. Coordination of the two commands is achieved by mutual inhibitory connections between them, ensuring that the motor neurons of the system receive only one command at a time. Some synaptic connections made by the command interneurons appear to be functionally ineffective; the possible significance of them is discussed. Available evidence suggests that many features of the network controlling circulation may be characteristic of other visceromotor systems of the abdominal ganglion.

Involvement of IgE in con A-induced histamine release from human basophils in vitro.

Abstract: CONCANAVALIN A (con A) induces the release of histamine from rat1 and hamster mast cells2 and human basophils. Time course, cationic requirements, enzymatic sequences and dose-response seem to be the same for con A-induced release as for antigen-induced release, which is mediated by reaginic antibody (reagin), believed to be bound by its Fc portion to a receptor in the membrane of the histamine-releasing cell. Human reagin is an antibody of the IgE class3. Antibodies4 specific for IgE can induce histamine release whereas the papain digest5 of those antibodies (which produces monomer anti-IgE) fails to elicit a response and can inhibit the intact anti-IgE-induced release6. The requirement for bridging to initiate histamine release has been established7–13. The types of sugar moieties to which con A binds have been studied14–17, and the physicochemical properties of con A15,18–22 indicate that at physiological pH it can bridge two or more of those sugar moieties. The question is raised as to whether con A is bridging sugar moieties at the receptor for reagin, or whether it is bridging sugar moieties which are directly attached to the reagin. The nature of the receptor remains to be established and the observation that con A can induce histamine release raised expectations that this interaction could elucidate some of the properties of this receptor.

Uptake and Integration of Transforming DNA in Bacillus Subtilis

Abstract: In the past decade, considerable information has accumulated concerning the molecular events that accompany the uptake and integration of transforming DNA by competent bacterial cultures. This article presents our understanding of the molecular events accompanying genetic transformation in Bacillus subtilis. The approach employed in our laboratory has been a straightforward one, involving the addition of isotopically and genetically labeled DNA to competent cells and the analysis of extracts of those cells.

Specialised transformation in Escherichia coli K12.

Abstract: A specialised transformation system has been developed in E. coli K12 by using specialised transducing phage DNA as donor DNA. Transformation of a marker on a F′ episome has also been achieved.

Fate of conjugally transferred DNA in minicells of Escherichia coli K-12.

Abstract: DNA-deficient minicells produced by an Escherichia coli F- strain can act as recipients for conjugally transferred DNA. When single-stranded [3H] thymidine-labeled Hfr DNA was transferred to minicells, 40 to 50% of the DNA could be degraded at 37°C in 3 hr into cold, trichloroacetic-acid-soluble material. Most of the acid soluble radioactivity was identified as thymine. The rates and amounts of DNA degradation were dependent on the temperature of incubation and on the pH and ionic makeup of the medium in which the minicells were suspended. Degradation was stimulated by the presence of Mg2+, Mn2+, and especially Ca2+ and was inhibited by Na+ and the absence of divalent cations and by the presence of dinitrophenol. The rates and amounts of degradation were greater in minicells harvested from stationary-phase cultures than in minicells from log-phase cultures. The results indicate that the DNA was degraded enzymatically and that both exonucleolytic and endonucleolytic activities were present in the minicells. From an analysis of undegraded DNA in minicells by alkaline sucrose gradient centrifugation, we infer that degradation is an all-or-none affair. Further, since the rates and amounts of DNA degradation observed in DNA-deficient F- minicells were similar to those in plasmid-containing minicells used as recipients for Hfr DNA, it can be inferred that the nucleases responsible for the degradation are cytoplasmic and are not bound to undamaged plasmid or chromosomal DNA.