29] Guanylate cyclase in human platelets

Abstract

Publisher Summary Human blood cells are separated by differential centrifugation and by use of Dextran. In plasma and homogenates of erythrocytes, no guanylate cyclase activity was detectable. In homogenates of mixed leukocytes (containing some platelets), the guanylate cyclase activity was about 50 pmoles min -1 mg protein -1 . The enzyme activity in platelets varied between 0.2 and 2.0 nmoles min -1 mg protein -1 this is substantially (up to an order of magnitude) higher than in any other mammalian tissue so far studied except outer segments of retinal rods. More than 90% of the total guanylate cyclase activity measured in subcellular fractions was found in the 250,000 g, 60-minute supernatant fluid. The apparent distribution of guanylate cyclase between particulate and soluble fractions was not affected by the mode of cell disintegration. Unlike the particulate guanylate cyclase activity from a number of other sources, that in platelets was not increased by Triton X-100. The enzyme in platelet homogenates or high speed supernatant fractions was inhibited by 50% by about 1 mg/ml of Triton X-100 in the incubation medium.