Abstract
Abstract Two tridecapeptides containing nonmethylated histidine residues have been isolated from tryptic digests of rabbit and bovine cardiac myosins with the following sequences, respectively: Leu-Leu-Ser-Ser-Leu-Asp-Ile-Asp-His-Gln-Asn-Tyr-Lys; Leu-Leu-Gly-Ser-Leu-Asp-Ile-Asp-His-Gln-Asn-Tyr-Lys. The peptides are homologous to the peptide containing 3-methylhistidine from rabbit skeletal muscle myosin (Huszar, G., and Elzinga, M. (1971) Biochemistry, 10, 229). There are four differences in the sequences of the rabbit skeletal and rabbit cardiac myosin peptides: Gly → Ser; Ile → Leu; Val → Ile; Thr → Asn. There is one difference in sequence between the cardiac peptides from rabbit and calf (Ser → Gly), indicating that this particular region of the primary structure of the myosin molecule is more similar in sequence in the same tissue from two different species than in heart and skeletal muscle of rabbit. All the amino acid replacements in the peptides are conservative and can be ascribed to single base changes. Based on the differences in the sequences of the cardiac histidine and skeletal 3-methylhistidine peptides from rabbit, it can be concluded that cardiac and skeletal myosin are synthesized under the control of different genes. The presence of nonmethylated histidine in cardiac myosins and the very conservative nature of the amino acid replacements around the histidine and 3-methylhistidine in cardiac and skeletal muscle myosins suggest to us that the lack of methylation is due to the absence of a histidine-methylating enzyme in cardiac muscle.
Highlights
The peptides are homologous to the peptide containing 3-methylhistidine from rabbit skeletal muscle myosin (HUSZAR, G., AND ELZINGA, M. (1971) Biochemistry, 10, 229)
The bovine and rabbit cardiac peptides differ slightly from each other but their sequences are very similar to the sequence around 3methylhistidine in rabbit skeletal muscle myosin
Preparation of Cardiac Myosin-Bovine cardiac myosin was prepared from fresh calf hearts, weighing 1 to 2 pounds, purchased from a local slaughterhouse
Summary
Two tridecapeptides containing nonmethylated histidine residues have been isolated from tryptic digests of rabbit and bovine cardiac myosins with the following sequences, respectively: Leu-Leu-Ser-Ser-Leu-Asp-Ile-Asp-His-GIn-. The presence of nonmethylated histidine in cardiac myosins and the very conservative nature of the amino acid replacements around the histidine and 3-methylhistidine in cardiac and skeletal muscle myosins suggest to us that the lack of methylation is due to the absence of a hlstidine-methylating enzyme in cardiac muscle. White skeletal muscle myosin has 2 moles per 5 x lo” g of protein, while cardiac myosin lacks this amino acid. In order to determine whether an appropriate site for methylation exists in cardiac muscle myosin we have looked for a peptide in cardiac myosin digests that corresponds to the 3-methylhistidine containing part of the white muscle myosin sequence. The bovine and rabbit cardiac peptides differ slightly from each other but their sequences are very similar to the sequence around 3methylhistidine in rabbit skeletal muscle myosin
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
