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Biomedical subjects

A Barth

Publications and source records attributed to A Barth.

At least 199 records · Page 11Linked to original sources
PubMed1984

Studies on the fatty acid synthesis of the perfused cirrhotic liver.

The fatty acid synthesis rate (using 3H2O incorporation experiments) and bile composition were studied in thioacetamide induced cirrhotic rat livers. The results show that the fatty acid synthesis rate of cirrhotic livers expressed as mumoles newly synthesized fatty acids per g liver is smaller than that of controls. Transient changes were observed in the incorporation pattern of newly synthesized fatty acids into individual lipid classes between cirrhotic and control livers. The output of bile acids is significantly decreased in cirrhotic livers.

Animals↗
PubMed1984

Similarities of the substrate cleavage catalyzed by proline specific endopeptidase and dipeptidyl peptidase IV.

16 substrates of the types succinyl-alanyl-alanine-pX-anilide, and succinyl-alanyl-proline-pX anilide having different substituents in para-position of the aryl residue were synthesized and characterized. The influence of electronic as well as hydrophobic substituent constants, sigma and pi, on the hydrolysis of the substrates catalyzed by the enzyme Proline Specific Endopeptidase (PSE) has been investigated. In the Hansch approach, the catalytic constants lg kcat and lg (kcat/KM) of succinyl-alanyl-alanine-pX-anilides hydrolyzed by PSE correlate significantly with electronic substituent constants sigma, whereas no correlation in the case of succinyl-alanyl-proline-pX-anilides. The intercorrelation of the constants of the former substrates with corresponding data from Dipeptidyl Peptidase IV (DP IV) catalyzed hydrolysis of alanyl-alanine-pX-anilides suggest that both enzymes act by similar catalytic mechanism.

Chemical Phenomena↗
PubMed1983

The conformation around the peptide bond between the P1- and P2-positions is important for catalytic activity of some proline-specific proteases.

Proline-containing dipeptidyl-4-nitroanilides have been synthesised and subjected to dipeptidyl peptidase IV-catalysed hydrolysis at high enzyme concentrations to collect information on the conformational specificity of the enzyme active site for a nonscissile bond. Descriptions of the biphasic kinetics were carried out in terms of cis/trans interconversion of the substrates. The results show that the enzyme can cleave only the trans-conformation of the substrate. The competitive inhibition by Gly-Pro-OH and Ala-Pro-OH is also specific for the trans form of the dipeptides. The interpretation of the results obtained from these kinetic studies has led to proposals for the stepwise cleavage of biologically active peptides like substance P and beta-casomorphine by dipeptidyl peptidase IV.

Animals↗
PubMed1983

N,O-diacylhydroxylamines as enzyme-activated inhibitors for serine proteases.

Several N-peptidyl-O(4-nitrobenzoyl)-hydroxylamines were synthesized and their inhibitory action against dipeptidyl-peptidase IV, alpha-chymotrypsin, elastase and thermitase was investigated. If the petidyl residue can be recognized by the enzyme as a substrate, a time dependent irreversible inactivation occurs. The mechanism of inhibition by N,O-diacylhydroxylamines as enzyme activated inhibitors is discussed.

Animals↗
PubMed1983

[Dipeptidyl peptidase activities in various organs of the Wistar rat].

Using Gly-Pro-pNa as a substrate, the authors photometrically determined the dipeptidyl peptidase activity in organic homogenates and serum of Wistar rats at two pH values. The activity of the serine peptidase DP IV was measured at pH = 7.6; a mixed activity (DP MA) which is composed of the activities of several dipeptidyl peptidases, at pH = 5.0. Particularly high DP IV activities were determined in the kidney, lung, adrenal gland, liver and aortic arch, the differences among the enzyme activities measured in the single organic homogenates at pH = 5.0 being smaller. The DP IV activities and the values found for DP MA in the structures of the nervous system were in general lower. Maximum DP IV values were measured in the spinal ganglion, cerebral cortex and spinal bulb; and maximum DP MA values, in the hypothalamus, cerebellum and cerebral cortex. The results obtained are discussed from the aspects of the participation of these enzymes in peptidergic regulatory mechanisms and of a possible relation to blood-pressure regulation.

Animals↗
PubMed1983

Comparative study on the antithrombotic effects of a synthetic thrombin inhibitor and of heparin in animal models.

The antithrombotic effects of the synthetic thrombin inhibitor 4-amidinophenylpyruvic acid and the naturally occurring thrombin inhibitor heparin were studied in a stasis-induced venous thrombosis model and an extracorporeal shunt model in rats. The incidence of venous thrombosis was reduced in a dose-dependent manner by both inhibitors. Thrombus size was reduced in the animals in which thrombi continued to form under treatment. The antithrombotic effect of the synthetic inhibitor was accompanied by considerable prolongation of the plasma thrombin time, whereas the effect of heparin on the thrombin time was less pronounced. The time until thrombotic occlusion of the extracorporeal arterio-venous shunt occurred was prolonged by both inhibitors in dependence upon the dose. The amount of thrombotic occluding material in the shunt was reduced and altered in composition. Synthetic thrombin inhibitors are potential antithrombotic agents whose effectivity corresponds to that of heparin.

Animals↗
PubMed1982

Judging models in QSAR- and LFE-like studies if there are no replications: correlation of dipeptidyl peptidase IV hydrolytic activities of L-Alanyl-L-alanine phenylamides.

Provided that the assumptions of regression analysis type I are met, an independent estimate of the standard deviation of the regressand using the method of near neighbors may be computed. The comparison of this estimate with the residual standard deviation obtained from a equation will reveal if there is some probability to get better equations not superimposed by chance correlation. A structure-activity relationship concerning the dependence of log Vmax for the hydrolytic cleavage of the substrates L-ala-L-ala-Y on physicochemical substituent constants demonstrates the usefulness of this procedure.

Catalysis↗
PubMed1982

[Synthesis and enzymatic degradation of beta-casomorphin-5 (author's transl)].

The authors describe the synthesis of beta-casomorphine-5 (Tyr-Pro-Phe-Pro-Gly) by segment condensation and stepwise building-up. Intracerebroventricular application of the pentapeptide to the rat produces a long-lasting analgesia against thermal stimuli (which can be inhibited by naloxone) and counteracts the extinction of a passive avoidance reaction for no less than 4 days following post-shock application. beta-Casomorphin-5 is very rapidly degraded by dipeptidylpeptidase IV; the degradation starts from the N-terminus giving dipeptides. The degradation products are competitive inhibitors of this enzyme.

Analgesics↗
PubMed1982

Excretion of lithium by kidney, bile and faeces in rats of different ages.

In 5-, 15- and 105-day-old rats the renal, biliary and faecal excretion of lithium was measured after administration of 150 mumol Li+/100 g b.wt. daily for two days and a load of 300 mumol Li+/100 g b.wt. intraperitoneally on the third day. The balance between the doses administered and elimination characterizes quantitative age-dependent differences concerning the two important excretion routes of lithium (kidney, faeces). Up to 72 hr after the 3rd lithium administration, in 5-day-old rats 50% of the total dose is excreted by kidney and approximately 40% in faeces. In 15- and 105-day-old rats, the renal elimination rate is distinctly higher: 80 or 90% of the lithium supply is excreted with urine and 15 or 10% with faeces, respectively. In both age groups only one fifth of the lithium eliminated with faeces is secreted via the bile. It is supposed that the major quantity of lithium secretion into faeces occurs through the intestinal mucosa. The results are in good accordance with findings of the age-dependent kinetics of lithium.

Age Factors↗
PubMed1981

pH-dependence of catalytic constants of the enzyme reaction--some remarks.

The influence of the hydrogen ion concentration on catalytic constants (kcat, KM and kcat/KM) was investigated under steady-state conditions where all steps of the Scheme, are taken into the consideration. The relative value of the rate constants has an influence on pH dependence of catalytic constants. The pH of intersection points of the tangents at the portion of functions pKM, Ig kcat, lg kcat/KM = f(pH) with different slopes are the values of true pKa of catalytically important ionizable groups in the free enzyme or in the enzyme-substrate complex(es), when the conditions k'-1, k'1, k'2 = 0 are valid. If e.g. k'-1, k'1 not equal to 0 the pH of the intersection points of the tangents is sometimes not the true value of the pKa. In this connection it is possible that more than one intersection point exists (in the plot lg kcat, pKM or lg kcat/KM versus pH) when only one ionizing group in the active site of an enzyme is present.

Catalysis↗