Showing papers by "Vanderbilt University published in 1969"
TL;DR: The molar ratio of FFA to Co in Co-FA complex was found to be 2.03, a cobaltous salt of fatty acid, and this factor of 2 can be used directly for the calculation of the FFA content in the unknown sample, reflecting the reliability of this method.
520 citations
TL;DR: A rapid technique for the determination of the dissociation constant and the number of binding sites of an enzyme-substrate complex has been developed based on measuring the rate of dialysis of radioactive substrate from an enzyme -substrate equilibrium mixture.
482 citations
TL;DR: There is a conformational change in the active center for phosphorylation during the normal reaction sequence and this change may be linked to one required theoretically for active translocation of ions across the cell membrane.
Abstract: In plasma membranes of intact cells an enzymatic pump actively transports sodium ions inward and potassium ions outward. In preparations of broken membranes it appears as an adenosine triphosphatase dependent on magnesium, sodium, and potassium ions together. In this adenosine triphosphatase a phosphorylated intermediate is formed from adenosine triphosphate in the presence of sodium ions and is hydrolyzed with the addition of potassium ions. The normal intermediate was not split by adenosine diphosphate. However, selective poisoning by N-ethylmaleimide or partial inhibition by a low magnesium ion concentration yielded an intermediate split by adenosine diphosphate and insensitive to potassium ions. Pulse experiments on the native enzyme supported further a hypothesis of a sequence of phosphorylated forms, the first being made reversibly from adenosine triphosphate in the presence of sodium ion and the second being made irreversiblyfrom the first and hydrolyzed in the presence of potassium ion. The cardioactive steriod inhibitor, ouabain, appeared to combine preferentially with the second form. Phosphorylation was at the same active site according to electrophoretic patterns of proteolytic phosphorylated fragments of both reactive forms. It is concluded that there is a conformational change in the active center for phosphorylation during the normal reaction sequence. This change may be linked to one required theoretically for active translocation of ions across the cell membrane.
460 citations
TL;DR: It is proposed that glucagon and possibly catecholamines play a role in the physiological regulation of gluconeogenesis from amino acids by increasing the formation of cyclic 3',5'AMP, which acts to stimulate both the transport of amino acids into the hepatic cell and the conversion of pyruvate to P-pyruvates.
410 citations
TL;DR: Guanyl cyclase, an enzyme catalyzing the formation of guanosine 3',5'-monophosphate from Guanosine triphosphate, has been identified in a variety of animal tissues and preliminary attempts to purify the enzyme by conventional techniques have yielded a purification of about 20-fold.
372 citations
TL;DR: Zonal centrifugation has been used to isolate a fraction from bovine liver which appears to be derived from the Golgi apparatus, and which has very high levels of galactosyl transferase.
Abstract: Zonal centrifugation has been used to isolate a fraction from bovine liver which appears to be derived from the Golgi apparatus. Morphologically, the fraction consists mainly of sacs and tubular elements. Spherical inclusions, probably lipoproteins, are occasionally seen in negative stains of this material. The preparation is biochemically unique. UDP-galactose:N-acetyl glucosamine, galactosyl transferase activity is concentrated about 40-fold in this fraction compared to the homogenate. Rotenone- or antimycin-insensitive DPNH- or TPNH- cytochrome c reductase activities are 60–80% of the level of activities found in microsomes. Purified organelles from bovine liver such as plasma membranes, rough microsomes, mitochondria and nuclei have negligible levels of galactosyl transferase. Some activity is present in smooth microsomes but at a level compatible with the possible presence of Golgi membranes in this fraction. The Golgi fraction does not contain appreciable amounts of enzymes such as ATPase, 5'-nucleotidase, glycosidase, glucose-6-phosphatase, acid phosphatase, or succinate-cytochrome c reductase. Similar fractions isolated from bovine epididymis also have very high levels of galactosyl transferase. The fraction is heavily osmicated when incubated for long periods of time at elevated temperatures, a characteristic property of Golgi membranes.
327 citations
269 citations
TL;DR: It is considered that, unlike free fatty acid, triglyceride fatty acid which accumulates in the livers of normal, fed rats is oxidized slowly, and that glucagon may not exert a major ketogenic action by stimulation of a hepatic triglyceride lipase.
267 citations
260 citations
TL;DR: An enzyme system which catalyzed the formation of cyclic GMP from GTP was demonstrated in small intestine, and this enzyme required Mn++ for maximal activity and was inhibited by ATP, suggesting a rapid turnover of the nucleotide in this tissue.
253 citations
TL;DR: It is postulated that hepatic rates of oxidation and ketogenesis from free fatty acids perfusing the liver are increased by glucagon and by cyclic AMP.
TL;DR: In this paper, a simplified method has been developed for the separation of plasma membrane material from isotonic homogenates of rat kidney, which consists of membrane vesicles free of nuclei and essentially free of intact mitochondria.
TL;DR: It is concluded that fatty acids probably do not play a physiological role in the rapid regulation of hepatic gluc oneogenesis, and that glucagon does not stimulate gluconeogenesis by activating hepatic lipolysis.
TL;DR: The liver has potent mechanisms to restore a displaced oxidation-reduction potential to normal and is virtually independent of the oxidation- reduction potential of the extramitochondrial NAD+-NADH couple as reflected by the lactate-pyruvate ratio of the tissue.
TL;DR: The changes in amino acid concentrations caused by glucagon resembled those found in diabetic animals and suggested a stimulation of intracellular utilization of glycine, alanine, glutamate, and phenylalanine.
TL;DR: A cyclic reaction sequence for inhibition of the enzyme by ouabain is proposed and related to physiological transport of sodium and potassium ions.
TL;DR: This suspension was utilized to study the in vitro effects of agents that have previously been shown to affect renin production in vivo, and it is suggested that the reninstimulating effect of catecholamines in the intact animal might be due, at least in part, to a direct chemical action on the renal cells.
Abstract: SummaryThe preparation of a dog renal cell suspension suitable for the study of renin production is described. This suspension was utilized to study the in vitro effects of agents that have previously been shown to affect renin production in vivo. Since production and destruction of renin could not be separately quantified, data were limited to “net production” of renin. Incubated controls had only slightly higher renin content than did the nonincubated controls, but the addition of epinephrine, norepinephrine or cyclic AMP caused striking increases in “net production” of renin. The effects of these agents on “net renin production” were abolished by cycloheximide, an inhibitor of protein synthesis. It is suggested that the reninstimulating effect of catecholamines in the intact animal might be due, at least in part, to a direct chemical action on the renal cells. Cyclic AMP may play a role as an intracellular mediator of the action of catecholamines.
TL;DR: It is suggested that an essential part of the insulin-effector system is a rapidly renewable peptide element located on the surface of the cell, and that an initial action of trypsin on the system mimics the effect of insulin while subsequent proteolytic modification of the system renders the cells unresponsive to the hormone.
TL;DR: In the present study both norepinephrine and melatonin were found to inhibit the increase in cyclic AMP levels in response to MSH, and both agents prevented or reversed MSH-induced darkening of frog skin.
Abstract: Evidence has previously been published indicating that melanocyte stimulating hormone (MSH) acts on the frog skin to increase intracellular concentrations of adenosine 3′,5′- monophosphate (cyclic AMP) and that this nucleotide in turn mediates the action of MSH in causing dispersion of melanin granules with consequent darkening of the frog skin. In the present study both norepinephrine and melatonin were found to inhibit the increase in cyclic AMP levels in response to MSH, and both agents prevented or reversed MSH-induced darkening of frog skin. Neither agent had any effect on frog skin darkening induced by exogenous cyclic AMP or on the in vitro enzymatic degradation of cyclic AMP. The inhibitory effects of norepinephrine on the actions of MSH were prevented by the α-adrenergic blocking agents dihydroergotamine and phentolamine, but these drugs were ineffective against melatonin. In contrast, the β-adrenergic agent isoproterenol had no significant inhibitory effect on MSH-induced cyclic AMP accumulation...
TL;DR: In this article, the polarizations of representative bands in the 1A2-1A1 systems of H2CO, D2CO and HDCO are determined by analysis of rotational fine structure of the absorption spectra.
TL;DR: A mixture of six purified anterior pituitary hormones completely reversed the effect of hypophysectomy on cyclic GMP excretion and proportionately more cyclicGMP than cyclic AMP was excreted, and the amounts of both nucleotides excreting in a day exceeded the total body content as measured at one point in time.
TL;DR: It was concluded that the lipoproteins in the Golgi apparatus are the precursors of plasma very low density lipoproteinins in blood plasma.
TL;DR: The study results add to the evidence that the level of cyclic AMP in blood platelets is an important determinant of the aggregation tendency of these cells.
TL;DR: Exogenous cyclic AMP mimicked the action of α-MSH in causing reversible dispersion of melanin granules in melanophores with resultant darkening of the skin and acted synergistically with α- MSH in increasing the dorsal skin content of cyclicAMP.
Abstract: The following evidence suggests that cyclic AMP is the mediator of MSH-induced darkening of the frog skin: 1. When added to the isolated frog skin, exogenous cyclic AMP mimicked the action of α-MSH in causing reversible dispersion of melanin granules in melanophores with resultant darkening of the skin. 2. α-MSH stimulated both cyclic AMP formation and darkening in dorsal skin but stimulated neither response in ventral skin. 3. Graded concentrations of α-MSH produced graded increases in cyclic AMP levels in the dorsal frog skin. 4. α-MSH, β-MSH and ACTH brought about increased cyclic AMP concentration in dorsal frog skin with the same relative potencies as they exhibited in stimulating frog skin darkening. 5. The increased cyclic AMP levels occurred at least as fast as darkening in response to α- MSH. 6. Theophylline (a known inhibitor of the cyclic 3′,5′-nucleotide phosphodiesterase which catalyzes cyclic AMP to 5′-AMP) acted synergistically with α-MSH in increasing the dorsal skin content of cyclic AMP....
TL;DR: Crystalline hexokinase prepared by the method of Darrow and Colowick consists largely of enzyme which has been modified in its chromatographic and electrophoretic behavior by yeast protease which is present during the isolation procedure.
TL;DR: In this article, the reaeration coefficient was shown to be proportional to the vertical mass transfer coefficient at the surface and inversely to the square of the average depth, which can be expressed as k2 = Cu\D*\N/h.
Abstract: The reaeration coefficient can be shown to be proportional to the vertical mass transfer coefficient at the surface and inversely proportional to the square of the average depth. After evaluation and simplification, this can be expressed as k2 = Cu\D*\N/h. The constant is evaluated from experimental data for various scales of flow and the resulting single equation is shown to have greater accuracy, cover a wider range of flow scales, and be less sensitive to variations in basic data than any of the presently used methods of prediction.
TL;DR: Whether the pituitary-adrenal cycle of normal man is synchronized by the dark-light cycle or by some other phenomenon associated with the sleepwake cycle is investigated.
Abstract: In order to determine whether the pituitary-adrenal cycle of normal man is synchronized by the dark-light cycle or by some other phenomenon associated with the sleepwake cycle, normal subjects underwent experimental alteration of their dark-light schedules in such a way that partial dissociation of the darklight schedules from the sleep-wake schedule was achieved. In addition, 3 blind subjects were studied. The normal subjects were allowed several days to become adapted to a given schedule prior to sampling of blood for plasma 17-hydroxycorticosteroid (17-OHCS) determinations. Hourly blood specimens were obtained through indwelling venous catheters in such a manner as to avoid disturbing sleep or exposing the subject to light during dark periods. Each subject slept 8 hr each day from 10 PM till 6 am, and the schedule of meals and activity was identical for all studies; only the dark-light schedule was altered. When the hours of darkness were scheduled in the middle of the waking day, from 10 am u...
TL;DR: A single injection of 100 μg of zinc was sufficient to rapidly reverse the effect of zinc deficiency on the synthesis of DNA in the rat.
Abstract: Dietary zinc deficiency has been shown to decrease the in vivo incorporation of thymidine into the nuclear DNA of liver parenchymal cells in the rat. A single injection of 100 μg of zinc was sufficient to rapidly reverse the effect of zinc deficiency on the synthesis of DNA.