Abstract
The modification of pyruvate kinase (PK) and lactate dehydrogenase (LDH) activity in foot muscle of the mussel Mytilus galloprovincialis during exposure to air and recovery in water was investigated. In the course of exposure to air, the activity of these enzymes measured at high and low substrate concentrations showed successive increases and decreases. Returning the mussels to water after exposure to air affected enzyme activity in a manner similar to anaerobiosis. When measuring at saturated concentrations of substrates and substrate and coenzyme for PK and LDH, respectively, the maximum activation of PK (37%) was observed at 4 h of animal exposure to air, and for LDH (67%) at 6 h exposure to air. During 24 h of exposure of animals to air, PK activity practically reached the stock level, while LDH was still activated (148%). The change in lactate dehydrogenase activity in mussel muscle during anoxia and recovery is described here for the first time. Variation in pyruvate kinase activity during exposure to air and recovery is linked to the alteration of half-maximal saturation constants and maximal velocity for both substrates. The possible role of reversible phosphorylation in the regulation of pyruvate kinase and lactate dehydrogenase properties is discussed.
Highlights
Glycolysis is a major mechanism for energy production during anaerobiosis in different organs of the sea mussels Mytilus edulis and M. galloprovincialis
The oxaloacetate formed is reduced in mitochondria to malate and this reduction regulates a coenzyme redox balance in the cytoplasm. The regulation of this branchpoint is provided by the reversible phosphorylation of pyruvate kinase (PK) which in the muscles of mussel is an allosteric enzyme [3,4,5]
The shape of the PK activity curve measured in the presence of 0.2 mM ADP and 1 mM PEP
Summary
Glycolysis is a major mechanism for energy production during anaerobiosis in different organs of the sea mussels Mytilus edulis and M. galloprovincialis. The oxaloacetate formed is reduced in mitochondria to malate and this reduction regulates a coenzyme redox balance in the cytoplasm. The regulation of this branchpoint is provided by the reversible phosphorylation of PK which in the muscles of mussel is an allosteric enzyme [3,4,5]. Since the activity of LDH in mussel tissues is rather low, under critical environmental conditions pyruvate is converted into octopine [6]. Owing to this modification the end product of glycolysis, lactate, is not accumulated in tissues. The properties of ODH have been investigated [6], but those of LDH and the effect of environmental factors on this enzyme activity have not been studied
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