Dehydrogenase in carbohydrate metabolism in larvae of the silkworm, Bombyx mori L.

Abstract

The dehydrogenases involved in both glycolytic and pentose phosphate pathways were studied with larval tissues of the silkworm, Bombyx mori L. The highest activity of G-6-P dehydrogenase and 6-PG dehydrogenase was found in the fat body. The purification of these two enzymes was partially carried out by precipitating with ammonium sulphate and successively by elution chromatography on a DEAE-cellulose column. The optimal pH for G-6-P dehydrogenase and 6-PG dehydrogenase was 7·7 and 8·3, respectively. The K m value of G-6-P dehydrogenase was 8·0 × 10 −5M and 3·1 × 10 −5M for G-6-P and NADP, respectively, and the K m value of 6-PG dehydrogenase was 7·0 × 10 −5M and 1·5 × 10 −5M for 6-PG and NADP, respectively. The midgut possessed high lactic dehydrogenase activity and the muscle moderate activity, whereas almost no activity was found in other tissues tested. The optimal pH for lactic dehydrogenase was 7·6, and the K m value of the enzyme for pyruvate was 1·0 × 10 −4M. The activity of lactic dehydrogenase was completely inhibited by 10 −4M of p-CMB. The activity of α-GP dehydrogenase was determined in larval tissues, and the ratio of α-GP dehydrogenase activity to lactic dehydrognase activity was obtained in several tissues. The results indicated that ratio varied specifically among different tissues. The occurrences of aldolase, phosphoglycerate kinase, and GAP dehydrogenase were also recognized in larval tissues.