CELLULAR AND SUBCELLULAR-LOCALIZATION OF HEXOKINASE, GLUTAMATE-DEHYDROGENASE, AND ALANINE AMINOTRANSFERASE IN THE HONEYBEE DRONE RETINA

Subcellular localization of hexokinase in the honeybee drone retina wa s examined following fractionation of cell homogenate using differenti al centrifugation. Nearly all hexokinase activity was found in the cyt osolic fraction, following a similar distribution as the cytosolic enz ymatic marker, phosphoglycerate kinase. The distribution of enzymatic markers of mitochondria (succinate dehydrogenase, rotenone-insensitive cytochrome c reductase, and adenylate kinase) indicated that the oute r mitochondrial membrane was partly damaged, but their distributions w ere different from that of hexokinase. The activity of hexokinase in p urified suspensions of cells was fivefold higher in glial cells than i n photoreceptors. This result is consistent with the hypothesis based on quantitative 2-deoxy[H-3]glucose autoradiography that only glial ce lls phosphorylate significant amounts of glucose to glucose-6-phosphat e. The activities of alanine aminotransferase and to a lesser extent o f glutamate dehydrogenase were higher in the cytosolic than in the mit ochondrial fraction. This important cytosolic activity of glutamate de hydrogenase was consistent with the higher activity found in mitochond ria-poor glial cells. In conclusion, this distribution of enzymes is c onsistent with the model of metabolic interactions between glial and p hotoreceptor cells in the intact bee retina.