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Biomedical subjects

N O Kaplan

Publications and source records attributed to N O Kaplan.

At least 19 recordsLinked to original sources
PubMed1979

Chelating agents protect hydrogenase against oxygen inactivation.

The effect of chelation on rate or air inactivation of hydrogenase from Clostridium pasteurianum has been investigated. All chelating agents used, whether water-soluble or water-insoluble, afforded protection against oxygen inactivation. EDTA appeared to be the most effective. Thus, in the absence of EDTA, hydrogenase in aqueous solution was nearly totally inactivated after 1 hour incubation in air, whereas 0.5 M EDTA (which did not affect significantly catalytic activity) allowed 41% retention of the initial activity even after 3 days incubation.

Chelating Agents↗
PubMed1979

Proton nuclear magnetic resonance study of the conformation and configuration of the cyclized pyridine nucleotide adducts.

We have closely examined by high-frequenty 1H nuclear magnetic resonance spectroscopy the structure of the adducts which form when various carbonyl compounds react with pyridine nucleotides at elevated pH. These studies show that the adducts of N-(2,6-dichlorobenzyl)nicotinamide-acetone, n-(2,6-dichlorobenzyl)nicotinamide-pyruvate, NMN-pyruvate, NAD-pyruvate, NAD-acetaldehyde, and NAD-oxaloacetate form with identical structural features as well as configuration. The following structural features are observed: (1) the adducts are pyridine N-4-substituted compounds; (2) a second six-membered ring forms by addition of the nicotinamide amido to the carbonyl group of the compound forming the addition complex; (3) cyclization occurs stereospecifically, indicating that the stereochemistry is predetermined by the initial attack at the N-4 position; (4) two diastereomeric forms are observed for each nucleotide adduct. Finally, the determination of configuration at all symmetric carbon atoms in these adducts will be discussed.

Acetaldehyde↗
PubMed1979

Antineoplastic activity of poly(L-lysine) with some ascites tumor cells.

We have found that poly(L-lysine) can be a very effective agent in preventing the growth of Ehrlich ascites tumors in mice. When given optimal doses of poly(L-lysine) (Mr 60 x 10(3)) intraperitoneally for 5 consecutive days, beginning on day 1 after inoculation with Ehrlich ascites cells. White Swiss mice show nearly a 100% remission from subsequent tumor growth. Rechallenge of "cured" animals with tumor cells, however shows no long-term immunological protection. In tissue culture, poly(L-lysine) shows a related potent cytotoxicity with HeLa cells; interestingly, the D isomer. In addition, there is a strong molecular weight dependence in that the small polylysine (Mr 3 x 10(3)) possesses less than 1/20th the cytotoxicity of large polymers (Mr 70 x 10(3)) on a weight basis in both cell culture and animal studies. At the same time, none of these lysine polymers gives any significant increase in life span to BDF1 mice infected with L1210 murine leukemia cells. We have also further explored the mechanism by which the polylysines express their cytotoxicity. These data indicate that lysine polymers show cell specificity in their action and in some cases they may be beneficial as potent antineoplastic agents, particularly when molecular weight is taken into consideration.

Animals↗
PubMed1978

Regulation of lactate dehydrogenase synthesis in Bacillus subtilis.

The regulation of lactate dehydrogenase in Bacillus subtilis was determined under a variety of growth conditions and in mutants blocked in the citric acid cycle. The synthesis of lactate dehydrogenase increased sharply concomitantly upon the exhaustion of glucose from the medium and the onset of the stationary phase. The synthesis of lactate dehydrogenase may be under catabolite repression control. Studies with mutants blocked in the citric acid cycle showed that lactate dehydrogenase is regulated independently of either the oxidative or reductase branches of the cycle. Certain citric acid cycle mutants, e.g., aconitase or succinate dehydrogenase, exhibited very low levels of lactate dehydrogenase while others, e.g., malate dehydrogenase or isocitrate dehydrogenase, showed normal levels. A stage O sporulation mutant expressed levels of lactate dehydrogenase more than one thousand-fold higher than the low group of citric acid cycle mutants. The induction of lactate dehydrogenase was shown to be independent of the accumulation of its substrate, pyruvate.

Aerobiosis↗
PubMed1978

The disulfide bond connecting the chains of ricin.

Studies on the disulfide bond connecting the two polypeptide chains of ricin are reported. Reduction of this bond in the native protein requires approximately 50-fold more mercaptoethanol than the reduction of the bond in the protein denatured by sodium dodecyl sulfate. An improved procedure for the formation of this disulfide bond from recombined chains is reported. A and B chains spontaneously and rapidly reassociate into a stable complex with a sedimentation velocity similar to that of native oxidized ricin before the disulfide bond reforms. The mixture of both chains also behaves on Bio-Gel P-100 like native oxidized ricin. However, the complex formed by the two chains, assayed before the disulfide bond can reform, and reduced ricin, carboxymethylated to prevent reoxidation, shows a significant decrease in toxicity to mice and a decrease in ability to inhibit protein synthesis in HeLa cells in culture.

Disulfides↗
PubMed1978

A rationale for stabilization of oxygen-labile enzymes: application to a clostridial hydrogenase.

A general procedure for stabilization of O2-labile enzymes exploiting "salting out" of oxygen from the microenvironment in the molecular layers immediately adjacent to charged surfaces of polyionic solid adsorbents has been developed. Empirical verification of this rationale is provided. The half-life of air inactivation of the O2-labile hydrogenase (EC 1.12.7.1) from Clostridium pasteurianum is increased 20- to 25-fold simply by adsorption (noncovalent binding) in dilute Tris.HCl buffer on common anion exchange supports such as DEAE-cellulose or Dowex 1-X2. Predicted increases in degree of stabilization by using more densely charged adsorbents (such as polyethyleneimine-cellulose), as well as bulkier solvent counter-anions, are found; half-lives for air inactivation for the bound hydrogenase can be increased to 3000-fold longer than that of the free enzyme. Most of the total catalytic activity, assayed as H2 evolution from dithionite mediated by methyl viologen or ferredoxin, is retained, whereas the expected suppression of H2 uptake in the reverse reaction is observed.

Adsorption↗