ENZYMES OF THE TRICARBOXYLIC ACID CYCLE IN SEA URCHIN EGGS AND EMBRYOS

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Abstract
Changes in the activity of some enzymes of the tricarboxylic acid cycle during development of sea urchins [Hemicentrotus pulcherrimus and Anthocidaris crassispina] were investigated. Unfertilized eggs showed substantial activity of citrate synthase, aconitase, NAD- and NADP-specific isocitrate dehydrogenases, fumarase and malate dehydrogenase. During development, the activity of citrate synthase, aconitase, NADP-specific isocitrate dehydrogenase and malate dehydrogenase increases gradually, whereas the activity of fumarase remains rather constant. There is no close correlation between changes in the enzyme activity and the increase in O2 consumption during development. Citrate synthase, aconitase and NADP-specific isocitrate dehydrogenase are mainly localized in the mitochondrial fraction, whereas fumarase and malate dehydrogenase are present in both mitochondrial and cytosol fractions. The intracellular localization of these enzymes does not change during development. A possible mechanism for the regulation of some enzymes of the tricarboxylic acid cycle in sea urchin eggs is discussed.