Co-Authors:
Pines, M., Department of Entomology, The Hebrew University, Rehovot, 76100, Israel
Applebaum, S.W., Department of Entomology, The Hebrew University, Rehovot, 76100, Israel
Abstract:
Locust fat body protein kinase is dependent on, and maximally stimulated by 5 × 10-6 M cyclic GMP and to a lesser extent by cyclic AMP. It exhibits a pH optimum of 6.9, an unusual requirement for high Mg2+ (maximum at 100 mM) or an alternative requirement for Mn2+ (maximum at 5 mM). Maximal stimulation by Mg2+ is twice that by Mn2+. Rabbit muscle protein kinase inhibitor uncharacteristically inhibits both cyclic AMP and cyclic GMP stimulated protein kinase activity of locust fat body, the former 5-fold more than the latter, with histone IIA as acceptor. The degree of phosphorylation differs for different acceptor proteins: histone IIA > locust vitellin > arginine-rich histone. Casein is barely phosphorylated and bovine serum albumin (fraction V) not at all. The high threshold for Mg2+ activation may be related to the high levels of Mg2+ in locust haemolymph, to the preferential phosphorylation of vitellin, and to the fact that the fat body is the site of vitellogenin synthesis. © 1978.
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