Size Scaling of Whole-Body Maximal Enzyme Activities in Aquatic Crustaceans

Abstract

The relationships between body size and maximal activities of eight enzymes were measured in whole-body homogenates of the crustaceans Macrobrachium rosenbergii, Artemia franciscana, and Daphnia magna. Interspecifically and intraspecificaily, enzyme activities per animal (Y) scale with protein weight (W) according to the allometric relationship Y = aWb. Scaling exponents (b) varied with the enzyme examined and were usually different from 0.75. For enzymes such as citrate synthase, intraspecific and interspecific exponents were similar, but for enzymes associated with pathways other than aerobic metabolism, significant differences were found between species. For anaerobic enzymes such as lactate dehydrogenase, these differences may relate to interspecific differences in life history and ecology. For anabolic enzymes such as glucose-6-phosphate dehydrogenase and nucleoside diphosphate kinase, differences may relate to differences in growth rates between species.