Biomedical subjects

M A Parniak

Publications and source records attributed to M A Parniak.

79 records · Page 5Linked to original sources

PubMed1984

Stimulation by glutamine of the formation of N6-hydroxylysine in a cell-free extract from Aerobacter aerogenes 62-1.

Glutamine may serve as an activator and/or regulator of the N6-hydroxylase (E.C. 1.14.99) of Aerobacter aerogenes 62-1. Activation and stabilization of N6-hydroxylase activity was observed both in vivo and in vitro. Growth in a glutamine-supplemented medium resulted in (1) maximum N6-hydroxylase activity at an earlier stage of growth and (2) higher N6-hydroxylase activity and continued aerobactin synthesis into stationary phase. Storage of P2 in the presence of L-glutamine (1 mM) significantly increased the lifetime of the labile N6-hydroxylase activity. Inclusion of L-glutamine in the incubation mixture typically resulted in a 2-3-fold activation of the hydroxylase activity. The stimulatory effect of glutamine was independent of and additive to the enhancement of N6-hydroxylation by the active component(s) in the supernatant, S2 fraction. Glutamic acid-gamma-semihydrazide activated slightly in the absence of glutamine but activation of the system by glutamine was decreased by this compound. Azaserine was shown to be an uncompetitive inhibitor with respect to lysine and this inhibition was not reversed by glutamine.

Azaserine↗

PubMed1983

Quantitative determination of monosubstituted guanidines: a comparative study of different procedures.

Analysis of N2-acyl arginine derivatives as well as of arginine analogs lacking in alpha-amino function by Weber's modification of the Sakaguchi procedure yielded colored complexes with absorbance values approximately twice that obtained with an equivalent concentration of unmodified arginine. The limitations concerning the applicability of the various modifications of the Sakaguchi procedure as well as of the fluorimetric assay to the quantitative estimation of a variety of monosubstituted guanidines and proteins are discussed.

Arginine↗

PubMed1981

Rat liver phenylalanine hydroxylase. Activation by sulfhydryl modification.

Upon reaction with N-ethylmaleimide, a single sulfhydryl residue/Mr = 50,000 subunit of phenylalanine hydroxylase is modified. This modification is accompanied by a 20-30-fold increase in hydroxylase activity when the activity is measured with tetrahydrobiopterin as cofactor. The N-ethylmaleimide-modified enzyme exhibits many of the characteristics of phenylalanine hydroxylase activated by partial proteolysis or by exposure to phospholipids. For example, a change from sigmoid to hyperbolic kinetics with varying phenylalanine concentration is observed, in addition to broadened substrate specificity and a dependence on phenylalanine hydroxylase stimulator protein at pH 6.8. The binding of phenylalanine to phenylalanine hydroxylase in the absence of pterin cofactor has also been studied. The native enzyme exhibits a sigmoidal phenylalanine binding curve. The N-ethylmaleimide-modified enzyme shows a hyperbolic response to phenylalanine binding in addition to an apparent decrease in total phenylalanine binding.

Animals↗

PubMed1979

Studies on the formation of N6-hydroxylysine in cell-free extracts of Aerobacter aerogenes 62-1.

We have investigated conditions optimal for the conversion of L-lysine to its N6-hydroxy derivative by partially purified cell-free extracts of Aerobacter aerogenes 62-1. The enzyme system was highly specific to L-lysine: the D-isomer and, the N2- or N6-derivatives of lysine, and alpha-amino acids were not hydroxylated. Most of the latter compounds had little effect onthe hydroxylation of L-lysine. However, -l-glutamic acid and L-glutamine enhanced the hydroxylation, with half-maximal activation achieved at 100 micrometers concentration of the effector. The Km values for pyruvate and L-(+)-lactate (compounds known to stimulate N-hydroxylysine formation) were found to be approx. 100 micrometers. The data show that N-hydroxylation of the amino acid precedes acylation in the biosynthesis of hydroxamic acid in A. aerogenes 62-1.

Antimetabolites↗

PubMed1977

Effect of metabolites on epsilon-N-hydroxylysine formation in cell-free extracts of Aerobacter aerogenes 62-1.

The conversion of L-lysine to its corresponding epsilon-N-hydroxy derivative has been achieved for the first time by cell-free extracts of Aerobacter aerogenes 62-1. Partial fractionation by differential centrifugation (at 12 000 X g) revealed that both supernatant and pellet are essential for maximum enzymatic activity. The omega-N-hydroxylase (EC 1.14.99) was found to function optimally at pH 7-7.5 and exhibited an apparent Km of about 75 muM for L-lysine. L(+)-Lactate or DL-lactate and pyruvate greatly stimulate the omega-N-hydroxylase activity. The system is strongly inhibited by arsenite and sulfite.

Arsenic↗

PubMedDate not supplied

Effect of substituting arabinonucleosides for deoxynucleotides in the DNA priming strand on the polymerase action of HIV-1 RT.

The ability of 5'-DNA-araN-3' chimeras to serve as primers during HIV-1 RT-catalyzed DNA synthesis was assessed. It is shown that while the structural changes imparted by the arabinose units are minimal, the biological outcome is significant. For example, a DNA strand with arabinocytidine (araC) at the 3'-terminus was found to serve as a primer of DNA synthesis but significant pausing of HIV-RT was observed after the addition of 4 dNTP's. This phenomenon was not observed for the analogous DNA primer containing a riboC unit or an all-DNA strand.

Arabinonucleosides↗

PubMedDate not supplied

Effects of copper and histidine on oxidative modification of low density lipoprotein and its subsequent binding to collagen.

It was previously shown that serum low density lipoprotein (LDL) binds to type I collagen gels and that the binding is increased after modification by cultured endothelial cells. It is now demonstrated that when LDL is incubated with cells cultured in Dulbecco's modified minimal essential medium (DMEM), the subsequent binding of LDL to collagen is considerably less than after incubation with endothelial cells cultured in Ham's F-12 medium (F12). To determine the reason for this difference, collagen gels were made with saline containing ingredients of DMEM individually or in groups, and binding of LDL to such gels was measured. Modification of LDL, manifested by a high level of binding to the collagen, by lipid peroxidation (production of thiobarbituric acid-reactive substances), and by increased electrophoretic mobility occurred on exposure to collagen gels made in saline; these changes were almost completely inhibited by the addition of histidine at a concentration equal to that in DMEM. They were also inhibited by butylated hydroxytoluene, desferrioxamine, and EDTA; penicillamine and hydroxyl-radical scavengers inhibited collagen binding but did not inhibit lipid peroxidation or the increase in electrophoretic mobility. Nominally, DMEM contains 270 microM histidine but no copper, whereas F12 contains 135 microM histidine and 10 nM copper; addition of copper (as much as 5 microM) to DMEM or of histidine (as much as 2.16 mM) to F12 did not overcome the differences between the media in supporting LDL oxidation by endothelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗