THE CONCENTRATIONS OF SOME ENZYMES OF THE CITRIC ACID CYCLE AND ELECTRON TRANSPORT SYSTEM IN THE LARGE GRANULE FRACTION OF EGGS AND TROCHOPHORES OF THE OYSTER, CRASSOSTREA VIRGINICA

¹ Department of Biology and Virginia Institute of Marine Science, College of William and Mary, Williamsburg, Virginia

1. The enzymes aconitase, TPN-specific isocitric dehydrogenase, alpha-ketoglutaric dehydrogenase, succinic dehydrogenase, fumarase, malic dehydrogenase, DPNH oxidase, and DPNH-cytochrome c reductase have been assayed in two fractions, large granules and supernatant, prepared from sucrose homogenates of fertilized eggs and trochophores of the oyster, Crassostrea virginica. Succinic dehydrogenase and DPNH oxidase are almost completely localized in the granules of the fertilized egg, but in the trochophore about of each enzyme is found in the supernatant fraction. High percentages of aconitase, isocitric dehydrogenase, and alpha-ketoglutaric dehydrogenase are found in the granules of both stages; the latter enzyme appears to be localized in the trochophore granules. Fumarase, malic dehydrogenase and DPNH-cytochrome c reductase are almost absent from granules of the egg, but considerable proportions of these enzymes are found in trochophore-granules.

2. Ratios of enzyme activities in the granules relative to that of succinic dehydrogenase have been determined at the two developmental stages. All of the enzymes except DPNH oxidase increase in activity, relative to the reference enzyme, in the granules during development to the trochophore stage. The activity of DPNH oxidase in the presence of cytochrome c is about the same as that of the succinic dehydrogenase in both stages. These changes appear to indicate that differentiation of the population of respiratory granules occurs during development of the oyster.