Structural Analysis of the Calcium-Binding Protein Calmodulin from Ascaris suum obliquely Striated Muscle

Abstract

Calmodulin was purified from the obliquely striated skeletal muscle of Ascaris suum. The calmodulin had a molecular weight of 16,400 and the amino acid composition indicated it is highly similar to other purified calmodulins, showing insignificant variation in 12 of 17 residues. In the residues that showed variation, a trend towards conservative substitution was observed. Spectrophotometric absorption maxima of 276 nm and 283 nm were observed. A molar absorption coefficient of 7,800 was calculated. Calcium-dependent binding to phenothiazine Affi-Gel confirmed that calcium binding induces conformation changes characteristic of calmodulin. Double reciprocal analysis of phosphodiesterase activation by A. suum calmodulin gave a Kapp of 40 nM.

Calcium and calmodulin antagonists inhibit human malaria parasites (Plasmodium falciparum): implications for drug design.

“…The parasitic roundworm Ascaris and three species of African trypanosomes have been shown to possess CaM (26,27). The phenothiazines have both weak anthelmintic properties and markedly inhibit trypanosome growth with disintegration of pellicular microtubules (28).…”