Synthesis of shrimp red pigment-concentrating hormone analogs and their biological activity in locusts.

Two analogs of the red pigment-concentrating hormone (RPCH) have been synthesized by the solid-phase method: [Thr6]-RPCH (I) and [Tyr4, Thr6]-RCPH (II). Analog I has the same amino acid composition as the second adipokinetic hormone (AKH-II) isolated from locust corpora cardiaca. Bioassay for lipid-mobilizing activity in adult male locusts gave the following increases in hemolymph lipid content: AKH-I, 3.5; I, 2.4; II, 2.9. The biological response shown by I lends support to the conclusion that its sequence is that of the presumptive AKH-II. Replacement of Phe in position 4 by Tyr does not reduce the adipokinetic response.