Search PubMed⌕ Search

Biomedical subjects

J Wallach

Publications and source records attributed to J Wallach.

50 records · Page 3Linked to original sources
PubMed1988

Conductimetry: a new tool for studying inhibition of elastolysis.

The conductimetric method was applied to the measurement of human leukocyte elastase activity, using insoluble elastin as a substrate. From conductance changes, initial rates of elastolysis were derived. A linear relationship of enzyme activity with enzyme concentration was demonstrated up to 400nM of enzyme, for three different substrates. In this concentration range, inhibition of elastolysis by eglin c was studied for different concentrations of eglin c. A 50% inhibitory concentrations of 0.13-0.15 microM of eglin c was derived from our results, corresponding to an inhibitor/enzyme ratio of about 0.5, indicating a strong inhibition, as previously demonstrated by authors using synthetic substrates.

Animals↗
PubMed1981

Effects of spironolactone and amiloride on corticosteroid-induced changes in colonic function.

Mineralocorticoid and glucocorticoid effects on colonic electrolyte absorption were compared by examining the alterations caused by spironolactone and amiloride in corticosteroid-treated rats. Animals were treated for 3 days with deoxycorticosterone acetate (DOCA; 0.5 mg . 100 g-1 . day-1), methylprednisolone (MP; 3 or 0.5 mg . 100 g-1 . day), and spironolactone (14 mg . 100 g-1 . day-1 im) singly or in combination. On day 4, rats were anesthetized with pentobarbital sodium and perfused in vivo with Ringer-HCO3 solution. Both doses of MP and DOCA increased net colonic sodium and water absorption and mucosal Na-K-ATPase activity. Concurrent spironolactone treatment completely prevented these effects in DOCA-treated rats but had no effect in MP-treated rats. Untreated, MP-treated, and DOCA-treated animals were perfused with a Ringer-HCO3 solution containing 1 mM amiloride. Amiloride reduced net colonic sodium and water absorption, transmural potential difference, and potassium secretion in all rats by approximately 55%. These effects were almost immediate and completely reversible. These findings in the rat suggest that 1) different receptors mediate the colonic effects of mineralocorticoids and glucocorticoids and 2) these corticosteroids do not differ in their relative effects on amiloride-sensitive and amiloride-resistant colonic sodium transport processes.

Adrenal Cortex Hormones↗
PubMed1981

Effect of Mg2+ and Ca2+ on enzymatic elastolysis of insoluble elastin determined by a conductimetric method.

The effect of some divalent cations on the elastolysis of insoluble elastin by pancreatic elastase has been studied with a conductimetric method. Mn2+ and Cu2+ give progressive inhibition, while Ca2+ initially slightly increases elastolysis, then becomes an inhibitor at concentrations higher than 10(-4) M. A stronger effect is demonstrated with Mg2+ which increases the initial velocity of the enzymatic reaction. However, there is no effect when N-succinyl-(Ala)(3)-paranitroanilide is used as the substrate. The different effects observed can be explained by an enzymatic activation process (cation-enzyme complex) and/or by a conformational change of the insoluble elastin.

Anilides↗
PubMed1980

Effect of Mg2+ and Mn2+ on hydrolysis of calf thymus DNA by pancreatic deoxyribonuclease I.

Divalent cations are activators for DNA hydrolysis by pancreatic deoxyribonuclease I. Apparent Vm and Km changes have been studied in presence of Mn2+ or Mg2+. The activation process modifies both Vm and Km, their relationship with Mg2+ or Mn2+ being a linear one. Deoxyribonucleotides inhibit the DNA hydrolysis, whether Mg2+ or Mn2+ is the activator; the purine deoxyribonucleotides are more effective as inhibitors than the pyrimidine ones. The effect of some derivatives of adenine has been studied: the inhibition is maximum with 5'-dAMP and minimum with adenine or adenosine. A kinetic mechanism of enzymatic activation by Mn2+ or Mg2+ is discussed.

Adenine Nucleotides↗
PubMed1980

Conductimetric study of the binding of Mn2+ to bovine pancreatic deoxyribonuclease.

The binding of Mn2+ on bovine pancreatic deoxyribonuclease has been studied by a conductimetric method. At low ionic strengths, a high-affinity single binding site is demonstrated. The association constant value (K = 1.2 x 10(5) M-1 at pH 8) is high enough to conclude that, in standard experimental conditions for DNA hydrolysis, the reacting species is the DNAase-cation complex. Competitive binding studies in presence of Mg++ and Ca++ show that these cations do not bind on the Mn++ site.

Animals↗
PubMed1977

Differential cardiovascular changes as a function of stimulation electrode site in rabbit hypothalamus.

Twenty chronically prepared, unanesthetized rabbits received both high-frequency (200 pulse/sec), short pulse-train (1.0 sec) and relatively low-frequency (25 pulse-sec), long pulse-train (10 sec) electrical stimulation of the hypothalamus. High-frequency, short pulse-train stimulation elicited a pressor response and bradycardia at all 27 electrode sites. In contrast, three other cardiovascular response patterns were obtained following low-frequency, long pulse-train stimulation. These latter patterns reflected a medial-lateral organization of autonomic function within the hypothalamus. Whereas all 15 lateral hypothalamic placements yielded depressor responses, 7 of 12 medial hypothalamic placements yielded pressor responses and tachycardia. Cardiovascular changes following administration of selective autonomic blocking agents (e.g., phentolamine, propranolol, methylatropine) suggest that high-frequency, short pulse-train stimulation elicited a pressor response followed by a reflexive bradycardia essentially mediated by an increase in vagal restraint. In contrast, the heart rate changes observed to low-frequency, long pulse-train stimulation all appear to have been importantly influenced by changes at the heart in beta-adrenergic activity.

Animals↗
PubMed1976

[The interaction between DNase I and the constituent deoxyribonucleotides of DNA].

A study of the interaction between deoxyribonucleotides and DNase I (E.C. 3.1.4.5) has disclosed a greater affinity of puric deoxyribonucleotides for the enzyme. DNase I showed one binding site for dAMP with an affinity constant of 2-4 X 10(4) M(-1). MnCl2 decreases the fixation of dAMP more effectively than MgCl2.

Adenine Nucleotides↗
PubMedDate not supplied

Lipopeptides with improved properties: structure by NMR, purification by HPLC and structure-activity relationships of new isoleucyl-rich surfactins.

The biosynthesis of bacterial isoleucyl-rich surfactins was controlled by supplementation of L-isoleucine to the culture medium. Two new variants, the [Ile4,7]- and [Ile2,4,7]surfactins, were thus produced by Bacillus subtilis and their separation was achieved by reverse-phase HPLC. Amino acids of the heptapeptide moiety were analysed by chemical methods, and the lipid moiety was identified by beta-hydroxy anteiso pentadecanoic acid by combined GC/MS. Sequences were established on the basis of two-dimensional NMR data. Because conformational parameters issuing from NMR spectra suggested that the cyclic backbone fold was globally conserved in the new variants, structure-activity relationships were discussed in details on the basis of the three-dimensional model of surfactin in solution. Indeed, both variants have increased surface properties compared with that of surfactin, and this improvement is assigned to an increase of the hydrophobicity of the apolar domain favouring micellization. Furthermore, the additional Leu-to-Ile substitution at position 2 in the [Ile2,4,7]surfactin leads to a substantial increase of its affinity for calcium, when compared with that of [Ile4,7]surfactin or surfactin. This effect is assigned, from the model, to an increase in the accessibility of the acidic side chains constituting the calcium binding site. Thus, the propensities of such active lipopeptides for both hydrophobic and electrostatic interactions were improved, further substantiating that they can be rationally designed.

Amino Acids↗