Enzymatic methylation of skeletal muscle contractile proteins

Abstract

The biological methylation of histidine and lysine residues in contractile proteins from the skeletal muscles of embryonic and posthatched chicks was studied. 3-Methylyhistidine-14C, and 14C-labeled ε-N-monomethyllysine, ε-N-trimethyllysine and 3-methylhistidine-14C were obtained from acid hydrolyzates of actin and myosin, respectively, following intraperitoneal injection of 6-day-old chicks with l-methionine-methyl-14C. Actin isolated from 9-, 11-, 14-, and 16-day-old embryonic chick skeletal muscle was deficient in 3-methylhistidine, reached normal levels at 18 days, and remained constant at all later ages. In in vitro, studies, whole skeletal muscle homogenates and myofibrillar fractions derived from homogenates catalyzed the transfer of the methyl group of S-adenosyl-l-methionine-methyl-14C to histidine and lysine residues of myofibrillar protein with synthesis of radioactive 3-methyl-histidine, ε-N-monomethyllysine, ε-N-dimethyllysine, and ε-N-trimethyllysine. The sarcoplasmic proteins also yielded these labeled methylated amino acid residues, except that ε-N-trimethyllysine incorporated higher levels of radioactivity and small amounts of labeled 1-methylhistidine were detected. Actin, isolated from the myofibrillar fraction after incubation with S-adenosyl-l-methionine-methyl-14C, contained radioactive 3-methylhistidine, ε-N-monomethyllysine and ε-N-dimethyllysine, while myosin from a similar reaction medium contained radioactive 3-methyl-histidine, ε-N-monomethyllysine and ε-N-trimethyllysine.