Proctolin, an activator of second messenger systems in insect visceral muscle tissue

Abstract

Proctolin, a pentapeptide isolated from hindgut tissue of the cockroach L. maderae, stimulates muscular contraction in that organ. It was the intention of this study to show that a second messenger system exists in the hindgut and that proctolin can effect this system. Adenylate cyclase derived from a 10,000 x g homogenate of the hindgut of L. maderae, is stimulated by low Ca²⁺concentrations (less than 100uM), calmodulin, and forskolin. The enzyme is inhibited by elevated Ca²⁺ concentrations (greater than 100 uM) and trifluoperazine. Proctolin is shown not only to bind reversibly to hindgut plasma membranes from L. maderae, but the peptide also has a direct and multiphasic action on adenylate cyclase. The myotropic activity of this peptide regulates hindgut muscle contraction through a second messenger system which involves both adenylate cyclase and calmodulin. The calcium binding protein calmodulin was isolated and characterized from hindgut tissue of L. maderae. The amino acid analysis, molecular weight, and U.V. absorption spectra are compared to calmodulin from bovine brain and Bombyx mori. A protocol for the isolation and purification of calmodulin using reverse phase high performance liquid chromatography was developed.