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N I Krinsky

Publications and source records attributed to N I Krinsky.

At least 91 records · Page 5Linked to original sources
PubMed1982

A kinetic analysis of the interaction of human myeloperoxidase with hydrogen peroxide, chloride ions, and protons.

The effect of H2O2, Cl-, and pH on human myeloperoxidase activity has been examined. The Km for H2O2 is shown to be affected by the combined presence of Cl- and acid pH conditions. The Km for H2O2 is independent of pH in the absence of Cl- and dependent on pH in the presence of Cl-. Conversely, the dependence of the Km for H2O2 on Cl- concentration increases as the pH decreases. A model is proposed in which Cl- has a dual role, acting both as a substrate and as an inhibitor. According to this model, the inhibitor Cl- binding site must be protonated prior to the binding of Cl- and is distinct from the substrate Cl- binding site which is unaffected by pH. The rate equation derived from this model is used to further analyze the data presented. The values of Km for H2O2 predicted by the rate equation are in good agreement with the experimentally determined values.

Chlorides↗
PubMed1982

Interaction of oxygen and oxy-radicals with carotenoids.

Dye-sensitized photo-oxidations of liposomes are inhibited by the presence of carotenoids in the membrane. Some carotenoid bleaching occurs during the reaction. It was shown that carotenoids are capable of inhibiting free-radical-induced lipid peroxidation in liposomes as well as singlet oxygen-induced lipid peroxidation. There is little direct effect of lipid peroxides on carotenoid bleaching during the photo-oxidative reactions. The carotenoid bleaching observed during the dye-photosensitized oxidations of the liposomes appears to be due to interactions between the carotenoid pigments and either radical intermediates from type I reactions or direct chemical reaction with singlet oxygen in a type II reaction. It was concluded that carotenoid pigments function as protective agents by quenching triplet sensitizers, singlet oxygen, and radical intermediates.

Carotenoids↗
PubMed1981

Superoxide, xanthine oxidase and platelet reactions: further studies on mechanisms by which oxidants influence platelets.

In the course of studying the effects on platelets of the oxidant species superoxide (O2.-), O2.- was generated by the interaction of xanthine oxidase plus xanthine. Surprisingly, gel-filtered platelets, when exposed to xanthine oxidase in the absence of xanthine substrate, were found to generate superoxide (O2.-), as determined by the reduction of added cytochrome c and by the inhibition of this reduction in the presence of superoxide dismutase. In addition to generating O2.-, the xanthine oxidase-treated platelets display both aggregation and evidence of the release reaction. This xanthine oxidase induced aggregation is not inhibited by the addition of either superoxide dismutase or cytochrome c, suggesting that it is due to either a further metabolite of O2.0, or that O2.- itself exerts no important direct effect on platelet function under these experimental conditions. The ability of C2.- to modulate platelet reactions in vivo or in vitro remains in doubt, and xanthine oxidase is an unsuitable source of O2.- in platelet studies because of its own effects on platelets.

Adenine Nucleotides↗
PubMed1981

The reductive cleavage of myeloperoxidase in half, producing enzymically active hemi-myeloperoxidase.

Reduction and alkylation of human myeloperoxidase under nondenaturing conditions results in the cleavage of this enzyme. Sedimentation equilibrium data is presented which shows that the molecular weight of the cleavage product (78,000 +/- 2,000) is half that of the native enzyme (153,000 +/- 4,000). We conclude that the cleavage product is the half-enzyme hemi-myeloperoxidase. Hemi-myeloperoxidase retains both heme groups and contains both subunit types (Mr = 57,500 and 14,000) in the same ratio as native myeloperoxidase. The two halves of native myeloperoxidase are apparently not dependent upon one another for peroxidatic activity, as the specific activity of the half-enzyme is the same as that of the native enzyme. Analytical ultracentrifugation studies show native myeloperoxidase has a sedimentation coefficient of 8.0 and an axial ratio of 5:1, while hemi-myeloperoxidase has a sedimentation coefficient of 4.3 and an axial ratio of 10:1. When [3H]iodoacetic acid was used to prepare hemi-myeloperoxidase, the label incorporated with a stoichiometry of 1.2 [3H]carboxymethyl groups per hemi-myeloperoxidase, with 90% of this label associated with the heavy subunit. From these observations we conclude that native myeloperoxidase contains two heavy-light protomers, which are joined along their long axes by a single disulfide bond between the heavy subunits. Selective reduction of this disulfide bond by the use of nondenaturing conditions results in the formation of hemi-myeloperoxidase, a catalytically active heavy-light protomer of native myeloperoxidase.

Acetylation↗
PubMed1981

Modification of platelet function by radical species produced during irradiation of oxygenated water.

Gel-filtered platelets in neutral, oxygen-containing solutions irradiated to a dose of 10 krad with gamma-rays display a significant inhibition of ADP-induced aggregation. Though the superoxide anion radical (O2-.) and H2O2 are generated in water irradiated under these conditions, only catalase, but not superoxide dismutase (SOD), conveyed protection against this inhibition of platelet function. When the platelets are in the presence of 10(-3) M sodium formate, which converts the majority of the radical species formed to O2-., inhibition of aggregation was again observed. Under these circumstances, the addition of catalase significantly decreased this inhibition, whereas the addition of SOD was without effect. In order to separate the platelet-inhibition effects of the radical species generated in the medium from a direct effect of irradiation on platelet components, relatively stable quantities of O2-. were produced in alkaline solutions and reacted with gel-filtered platelets. Again, an inhibition of ADP-induced aggregation was observed. This inhibition was not significantly altered by the addition of SOD, but was abolished by the addition of catalase, either with or without SOD. Our observation would indicate that O2-. is without direct effect on platelet function, but serves as the precursor of H2O2, which can inhibit platelet reactions.

Adenosine Diphosphate↗
PubMed1981

Effect of corticosteroids on the production of superoxide and hydrogen peroxide and the appearance of chemiluminescence by phagocytosing polymorphonuclear leukocytes.

Human polymorphonuclear leukocytes were incubated with either methylprednisolone sodium succinate, hydrocortisone sodium succinate, or distilled water, and then latex spherules were added as target particles for phagocytosis. At low concentrations of these corticosteroids (0.04-0.22 mM), no effect was observed on O2-. production, H2O2 production, or chemiluminescence. At high concentrations of these steroids (2.7 mM), a significant inhibition was observed in both O2-. production and H2O2 production. At 2.7 mM, methylprednisolone sodium succinate significantly decreased chemiluminescence, whereas hydrocortisone sodium succinate was without effect on chemiluminescence.

Adrenal Cortex Hormones↗
PubMed1977

Source of hydrogen peroxide and of chemiluminescence observed in activated human platelet preparations.

Human platelet suspensions can be observed to produce small amounts of H2O2 (0.04 nmoles H2O2/min/2.5 X 10(5) cells/cu mm) and measurable chemiluminescence when exposed to target particles for phagocytosis, such as latex spherules. Both H2O2 production and chemiluminescence are characteristic of phagocytosing polymorphonuclear leukocytes (PMN) and analysis of the purified platelets indicates contamination by PMN at the level of 0.2%. The amount of H2O2 produced and the chemiluminescence observed can be duplicated by adding latex spheres to a preparation of PMN at a concentration equivalent to the contaminant in the platelet preparations. We conclude that the H2O2 produced and chemiluminescence observed from activated platelets is due to the presence of small amounts of contaminating PMN. These studies emphasize the importance of controlling for PMN contamination in studies of platelet biochemistry and physiology.

Adenosine Diphosphate↗
PubMed1976

Leukocyte-platelet interaction. Release of hydrogen peroxide by granulocytes as a modulator of platelet reactions.

Because of the many potent biological capabilities of the blood granulocytes, and their contact with platelets in various physiologic and pathologic states, a possible interaction between granulocytes and platelets was investigated. Platelets were purified by gel filtration and via a dialysis membrane were separated from suspensions of autologous granulocytes prepared by dextran sedimentation and resuspended in modified Tyrode's buffer. After 20 min at 37 degrees C platelet aggregation was shown to be diminished by such exposure, as compared to the aggregation of platelets incubated with dialysates of buffer only. When granulocytes were stimulated by the addition of 1.1-muM latex spheres as target particles for phagocytes, the dialysate of these cells exhibited greatly enhanced platelet-inhibitory properties. The addition of catalase to the platelets abolished the effect of exposing these cells to the dialysate of resting granulocytes and markedly inhibited the effect of exposing the platelets to the dialysate of phagocytosing granulocytes. Catalase treated with 3-amino-1,2,4-triazole had no platelet-protective capacity. Purified suspensions of lymphocytes released no platelet-inhibitory principle under these experimental conditions. Hydrogen peroxide in the dialysate of granulocytes was measured directly with an assay involving an H2O2-induced decrease in the fluorescence of scopoletin catalyzed by horseradish peroxidase. The dialysate of phagocytosing granulocytes contained 0.86 +/- 0.55 nmol H2O2/2.5 X 10(7) granulocytes when sampled at 20 min. By an alternate measurement technique in which scopoletin and horseradish peroxidase were present in the dialysate from time zero, the mean amount of H2O2 in the dialysate reached 4.0 +/- 1.3 nmol/2.5 x 10(7) granulocytes at 20 min. This discrepancy suggested the consumption of H2O2, possibly mediated by the granulocytes themselves. This possibility was investigated by the addition of exogenous H2O2 to the test system. Both granulocytes and platelets enhanced the disappearance of H2O2 from the dialysate, and the amount consumed was proportional to the amount of H2O2 added to the system. Glucose oxidase at 12 M U/ml plus glucose in excess resulted in the production of H2O2 at a rate and final amount comparable to that produced by phagocytosing granulocytes. This mixture, when substituted for phagocytosing granulocytes in the standard dialysis membrane experiment, induced an inhibition of platelet aggregation similar to that caused by the granulocytes. The observation that the release of H2O2 by the blood granulocyte influences platelet function suggests a potential role for the granulocyte in the regulation of hemostasis or thrombosis.

Adenosine Diphosphate↗
PubMed1974

Singlet excited oxygen as a mediator of the antibacterial action of leukocytes.

Human polymorphonuclear leukocytes kill a colorless mutant strain of Sarcina lutea much more readily than a carotenoid-containing strain. A similar protective effect has been reported in the organism during photodynamic inactivation, where it is attributable to the quenchintg of singlet excited oxygen by carotenoids. The findings with leukocytes support the suggestion that singlet excited oxygen acts as one of the mediators of their bactericidal action.

Bacteriolysis↗