We have isolated two Ca2+-binding proteins from squid optic lobes, each of which is also able to bind phenothiazines in a Ca2+-dependent manner. These proteins have each been purified and partly characterized. One of the proteins corresponds to calmodulin, in that it has a similar amino acid content to bovine brain calmodulin, including a single residue of trimethyl-lysine, it co-migrates with bovine calmodulin both on alkaline-urea- and on sodium dodecyl sulphate (SDS)/polyacrylamide-gel electrophoresis, and will activate calmodulin-dependent phosphodiesterase. The second protein has the same subunit molecular weight as calmodulin, as determined by SDS/polyacrylamide-gel electrophoresis, Mr 17 000, but migrates more slowly than this protein on alkaline-urea-gel electrophoresis. It has an amino acid composition distinct from calmodulin, containing no trimethyl-lysine, its CNBr fragments migrate on alkaline gels in a pattern distinct from those of calmodulin and it shows little ability to activate phosphodiesterase. The u.v.-absorption spectra of the proteins indicate the absence of tryptophan and the presence of a high phenylalanine/tyrosine ratio in each. Both proteins also bind 3-4 calcium ions/mol at 0.1 mM-free Ca2+ and each binds chlorpromazine in a Ca2+-dependent manner.
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March 1983
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Research Article|
March 01 1983
Two low-molecular-weight Ca2+-binding proteins isolated from squid optic lobe by phenothiazine-Sepharose affinity chromatography
Publisher: Portland Press Ltd
Online ISSN: 1470-8728
Print ISSN: 0264-6021
© 1983 London: The Biochemical Society
1983
Biochem J (1983) 209 (3): 797–802.
Citation
J F Head, S Spielberg, B Kaminer; Two low-molecular-weight Ca2+-binding proteins isolated from squid optic lobe by phenothiazine-Sepharose affinity chromatography. Biochem J 1 March 1983; 209 (3): 797–802. doi: https://doi.org/10.1042/bj2090797
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