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3-methylhistidine in actin and other muscle proteins.

ABSTRACT: 1. By the use of the extended elution system for basic amino acid analysis, 3-methylhistidine has been detected in hydrolysates of actin isolated from mammalian, fish and bird skeletal muscle. 2. Evidence is presented to indicate that 3-methylhistidine forms part of the primary structure and that in rabbit actin this residue is restricted to one peptide fraction obtained from the tryptic digest. 3. Rabbit skeletal-muscle actin has a 3-methylhistidine:histidine ratio 1:7.6, indicating a minimum molecular weight of 47600. 4. Adult rabbit myosin contains approximately 2 3-methylhistidine residues/mol. These residues are localized in the heavy meromyosin part of the molecule, and are restricted to the major component obtained after succinylation.

SUBMITTER: Johnson P

PROVIDER: S-EPMC1198308 | biostudies-other | 1967 Oct

REPOSITORIES: biostudies-other

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Project description:The turnover of 3-methylhistidine (N tau-methylhistidine) and in some cases actin, myosin heavy chain and aldolase in skeletal muscle was measured in a number of experiments in growing and adult rats in the fed and overnight-starved states. In growing fed rats in three separate experiments, measurements of the methylation rate of protein-bound 3-methylhistidine by either [14C]- or [3H]-methyl-labelled S-adenosylmethionine show that 3-methylhistidine synthesis is slower than the overall rate of protein synthesis indicated by [14C]tyrosine incorporation. Values ranged from 36 to 51%. However, in one experiment with rapidly growing young fed rats, acute measurements over 1 h showed that 3-methylhistidine synthesis could be increased to the same rate as the overall rate. After overnight starvation in these rats, the steady-state synthesis rate of 3-methylhistidine was 38.8% of the overall rate. This was a similar value to that in adult non-growing rats, in which measurements of the relative labelling of 3-methylhistidine and histidine after a single injection of [14C]histidine indicated that 3-methylhistidine synthesis was 37% of the overall rate in the fed or overnight-starved state. According to measurements of actin, myosin heavy-chain and aldolase synthesis in the over-night-starved state with young rats, with a variety of precursors, slow turnover of 3-methylhistidine results from the specific slow turnover of actin, since turnover rates of myosin heavy chain, mixed protein and aldolase were 2.5, 3 and 3.4 times faster respectively. However, in the fed state synthesis rates of actin were increased disproportionately to give similar rates for all proteins. These results show that (a) 3-methylhistidine turnover in muscle is less than half the overall rate in both young and adult rats, (b) slow 3-methylhistidine turnover reflects the specifically slow turnover of actin compared with myosin heavy chain and other muscle proteins, and (c) during growth the synthesis rate of actin is particularly sensitive to the nutritional state and can be increased to a similar rate to that of other proteins.

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3-methylhistidine in actin and other muscle proteins.

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