Peptides related to the calcium binding domains II and III of calmodulin

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Abstract
Three hexadecapeptides which correspond to the putative Ca2+ binding domains II and III of calmodulin were synthesized employing solid phase methodology. One of the peptides contained an internal cystine bridge which was formed while the corresponding linear peptide was still attached to the polymeric carrier. The interaction of the synthetic peptides with calcium ions was investigated using Tb3+-mediated fluorescence. Binding was of the order Cal2 > Cal3 > Cal3C (Fig.1) with binding constants KTb3+=0.68 .times. 10-5, 0.54 .times. 10-5, and 0.21 .times. 10-5 M-1 respectively. Biological activity of the compounds was assessed by measuring their stimulatory effect on erythrocyte membrane (Ca2+ + Mg2+)-ATPase activity. For 50% activity as compared with CaM, the concentration of peptides required was for Cal2, Cal3 and Cal3C, 50, 100 and 167 times higher than CaM, respectively. The results suggest that the three synthetic peptides possess certain calmodulin-like features.

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