Two low-molecular-weight Ca2+-binding proteins isolated from squid optic lobe by phenothiazine--Sepharose affinity chromatography.
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.
D015105:3',5'-Cyclic-AMP Phosphodiesterases / Q000378:metabolism; D000596:Amino Acids / Q000032:analysis; D000818:Animals; D002135:Calcium-Binding Proteins / Q000302:isolation & purification* / Q000494:pharmacology; D002147:Calmodulin / Q000302:isolation & purification; D002746:Chlorpromazine / Q000378:metabolism; D002846:Chromatography, Affinity / Q000379:methods; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D049832:Decapodiformes / Q000032:analysis*; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation / Q000187:drug effects; D008970:Molecular Weight; D009899:Optic Lobe, Nonmammalian / Q000032:analysis*; D010640:Phenothiazines; D013056:Spectrophotometry, Ultraviolet
D000596:Amino Acids; D002135:Calcium-Binding Proteins; D002147:Calmodulin; D010640:Phenothiazines; D015105:3',5'-Cyclic-AMP Phosphodiesterases; D054677:Cyclic Nucleotide Phosphodiesterases, Type 1; D002746:Chlorpromazine