Invertebrate calmodulins of the sea anemone and scallop muscle were isolated and their properties were compared with those of vertebrate calmodulins from rabbit muscle and pig brain. The molecular weights estimated by SDS-polyacrylamide gel electrophoresis were similar to the molecular weight (16,500) of the vertebrate calmodulins. Every calmodulin contained 1 mol each of trimethyllysine and histidine, and high contents of acidic amino acids. The marine invertebrate calmodulins contained only one tyrosine in contrast to two tyrosines in the vertebrate ones. As a result, the UV absorption spectra were clearly different. The Ca2+-induced difference UV absorption spectra of the invertebrate calmodulins were indistinguishable from those of the vertebrate ones in spite of the difference in tyrosine contents. In tryptic peptide maps of invertebrate calmodulins, a few spots different from those of vertebrate calmodulins were observed in the basic and acidic peptide regions. The calmodulins of invertebrate muscles and that of rabbit skeletal muscle were almost indistinguishable in terms of the activation profile of rabbit skeletal myosin light chain kinase.
Yazawa et al. (Tue,) studied this question.