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Oxidation of NADH in a Coupled Oxidase‐Peroxidase Reaction and its Significance for the Fermentation in Rumen Protozoa of the Genus Isotricha
Author(s) -
PRINS R. A.,
PRAST E. R.
Publication year - 1973
Publication title -
the journal of protozoology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.067
H-Index - 77
eISSN - 1550-7408
pISSN - 0022-3921
DOI - 10.1111/j.1550-7408.1973.tb00929.x
Subject(s) - chemistry , hydroxylamine , fermentation , biochemistry
SYNOPSIS. Cell‐free extracts of the anaerobic rumen ciliate Isotricha prostoma possess a strong NADH oxidase activity. Evidence for H 2 O 2 as an intermediary product during oxidation of NADH has been obtained. Gatalase activity could not be demonstrated but hydrogen peroxide is removed by a rate limiting NAD peroxidase. In addition to oxygen several other compounds such as ferricyanide, cytochrome c , menadione and certain dyes may function as electron acceptors during oxidation of NADH. The ferricyanide reductase activity in the Isotricha extracts strongly resembles that of the mitochondrial enzyme from mammalian sources in a number of characteristics. Partial inhibition of NADH oxidase activity was obtained with the following chelating agents: hydroxylamine, diethyl dithiocarbamate, 2,9‐dimethyl‐1,10‐phenanthroline (DMPH), and 2‐thenoyl trifluoroacetone, whereas citrate, tartrate, pyrophosphate, salicylaldoxime, EDTA and 8‐hydroxyquinoline had no effect. The peroxidase was blocked completely by 0.42 mM DMPH and this inhibitor was used to block the enzyme in whole cells in experiments on oxygen toxicity. The oxidase was largely insensitive to azide, KCN, and uncouplers. Antimycin A and rotenone caused a partial inhibition of the oxidase when added in very high concentrations. ATP formation occurred during oxidation of NADH, and P/O ratios were 0.1–0.35. Addition of small amounts of oxygen to intact ciliates led to a decrease in the production of hydrogen and butyrate, while the production of acetate was increased and no change in the lactate formation was seen. This shift in fermentation end‐products possibly is caused by a competition of oxygen for NADH.