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. 1973 Feb;113(2):637–644. doi: 10.1128/jb.113.2.637-644.1973

Succinate Oxidase in Neurospora

David J West 1, Dow O Woodward 2
PMCID: PMC285275  PMID: 4266173

Abstract

Two kinetically distinct states of succinate oxidase have been detected in the mitochondria of Neruospora crassa. One state has a Km for succinate of 4.1 × 10−3m, and the other has a Km for succinate of 3.5 × 10−4m. The high Km state was found in freshly extracted mitochondria from either 20- or 72-hr mycelium. However, the succinate oxidase activity in mitochondria from 20-hr mycelium rapidly deteriorated in vitro, leaving a stable residual activity with the lower Km for succinate. Adenosine triphosphate (ATP) plus Mg2+ stabilized the high Km state in these preparations. The high Km state of succinate oxidase was further characterized by a two- to threefold increase in activity over the pH range 6.6 to 8.0 and by classical competitive inhibition by fumarate and malonate. By contrast, the low Km state of succinate oxidase showed a relatively flat response to pH over the range 6.6 to 8.0 and a nonclassical pattern of inhibition by fumarate and malonate, as shown by nonlinear plots of reciprocal velocity versus reciprocal substrate concentration in the presence of inhibitor or reciprocal velocity versus inhibitor concentration at fixed substrate concentrations. The relationship of mycelial age to the in vitro stability of succinate oxidase is considered with reference to probable changes in the relative pool sizes of extra- and intramitochondrial ATP in response to changes in the rate of glycolysis.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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