3′-phosphoadenosine-5′-phosphosulphate synthesis and involvement in sulphotransferase reactions in the insect, Spodoptera littoralis

Abstract

Synthesis of 3''-phosphoadenosine-5''-phosphosulfate from ATP and 35SO42- was demonstrated in homogenates of gut, Malpighian tubules and fat body of S. littoralis. The enzyme system was most active in the gut tissue and was primarily located in the cytosol fraction of the cell. Gut cytosol preparations were used as a source of the 3''-phosphoadenosine-5''-phosphosulfate generating system for more detailed studies. Maximum synthesis required an incubation mixture containing Tris/HCl buffer (pH 7.5), ATP (20 mM), MgCl2 (13.0 mM) and K2SO4 (3 mM). The specific activity of the 3''-phosphoadenosine-5''-phosphosulfate synthesizing activity in gut cytosol increased during development of the 6th instar larva, reaching a peak at day 4. A sudden fall in specific activity was observed in the prepupal stage. 3''-Phosphoadenosine-5''-phosphosulfate formation is the rate limiting process in the overall sulfation of p-nitrophenol in the gut cytosol preparations from S. littoralis. The properties of the sulfate-activating system in this insect are similar to those reported for vertebrates.