Guanylate cyclase (E.C. 126.96.36.199.) was investigated in the accessory reproductive gland of the male house cricket, Acheta domesticus, which is known to accumulate exceptionally high levels of guanosine 3′,5′-cyclic monophosphate (cyclic GMP). Accessory gland guanylate cyclase activity was linear with time for at least one hour, and with enzyme concentration to about 5 mg soluble protein per ml. Activity was dependent on Mn2+ and was maximal at pH 7.3 to 8.0. Sodium fluoride had no effect on activity, but sodium azide was slightly stimulatory. About 80% of the activity was sedimentable at 16,000 g, and both soluble and particulate activities were increased slightly in the presence of Triton X-100. Kinetic analysis indicated half-maximal velocity at 85 μM GTP in the presence of excess Mn2+, and reciprocal plots were concave upward. Changes in activity during maturation of the gland were small, and did not provide evidence for a regulatory role of guanylate cyclase in the accumulation of accessory gland cyclic GMP. The regulation and rôle of cyclic GMP in the accessory gland are discussed.
Bibliographical noteFunding Information:
Acknonlrclyetnrrirs-This research was supported by grants from the U.S. National Institutes of Health (HD-0795 1)a nd the National Research Council of Canada.