蓖麻蚕γ-谷氨酰转肽酶的研究

L-γ-谷氨酰转肽酶(γ-GTP)广泛分布在蓖麻蚕Philosamia cynthia ricinI的中肠、马氏管、后丝腺、脂肪体、体壁等组织中;并存在于蚕个体发育中的各个阶段。酶活力以马氏管、中肠为最大。在五龄蚕前中期各组织均显示γ-GTP最大活力。在脂肪体和表皮组织中,蛹形成时又分别出现γ-GTP活力峰。昆虫生长发育必需的10种氨基酸均是蚕各组织γ-GTP酶促反应的受体。这些结果表明,γ-GTP作为L-γ-谷氨酰循环中一个关键酶,在蓖麻蚕体内对氨基酸的吸收和转运起着重要作用。

STUDIES ON γ-GLUTAMYL TRANSPEPTIDASE IN PHILOSAMIA CYNTHIA RICINI

Activities of y-glutamyl transpeptidase (y-GTP) in the midgut, Malpighian tubules, posterior silkgland, fat body and integument of the eri-silkworm Plmlosamia cynthict ricini were determined by using y-glutemyl-r-natroanilidae as the substrate. The specific activities in Malpighian tubules and midgut were higher than in other tissues. The r-GTP activities in these two tissues reached the maxima on the second day to the fourth day of the fifth instar, since then they began to decline rapidly. The r-GTP activity in the fat body and integument rose to maxima just after pupation and then decreased and became virtually undeteetable at the close of pupal stage. But the r-GTP activity in the fat body would rise again after adult; emergence.The biochemical study on. the cri-silkworm r-GTP revealed that, the essential amino acids required for insect growth could serve very well as the receptors of this enzyme. The optimal pH for the y-GTP activity ranged from 8.0 to 9.0 in different tissues. The enzymie activity was sensitive to the inhibition of L- and D-r-glutamyl-(O-carboxy)-phenyl-hydi-azide and scrine-borax.Our study confirms that y-GTP is intimately related to amino acid absorption, transportation and transformation and finally to protein synthesis aaid development of the eri-silkworm.