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The primary structure of the calcium-transporting adenosine triphosphatase of rabbit skeletal sarcoplasmic reticulum. Soluble tryptic peptides from the succinylated carboxymethylated protein.

ABSTRACT: The isolation and the determination of the amino-acid sequences of the soluble tryptic peptides, derived by cleavage at arginine residues, of the succinylated (3-carboxypropionylated) S-carboxymethylated adenosine triphosphatase protein of rabbit skeletal sarcoplasmic reticulum are described. Treatment of the protein with succinic anhydride gave a derivative that was readily digested with trypsin, yielding two distinct sets of peptides. One set comprises large, relatively hydrophobic, peptides that are highly aggregated (or insoluble) in aqueous solution and that have been identified, by several criteria, with the portion of the protein embedded in the lipid bilayer in the sarcoplasmic reticulum. The second set, which is described here, comprises peptides that have properties typical of those derived from soluble globular proteins and that constitute that part of the protein external to the lipid bilayer. The sequences of these soluble tryptic peptides contain 586 unique residues. Details of the isolation of the peptides and the determination of the sequences are contained in Supplementary Publication SUP 50102 (88 pages) which has been deposited with the British Library Lending Division, Boston Spa, Wetherby, West Yorkshire LS23 7BQ, U.K., from whom copies can be obtained on the terms indicated in Biochem. J. (1978) 169, 5.

SUBMITTER: Allen G

PROVIDER: S-EPMC1162440 | biostudies-other | 1980 Jun

REPOSITORIES: biostudies-other

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Project description:The ATPase (adenosine triphosphatase) from sarcoplasmic reticulum contains 20 thiol groups/115000 daltons, measured by using either N-ethyl[(14)C]maleimide or 5,5'-dithiobis-(2-nitrobenzoate) in sodium dodecyl sulphate. After reduction there were 26 thiol groups, in good agreement with 26.5 residues of cysteic acid found by amino acid analysis. The difference between this and the 20 residues measured before reduction implies the presence of three disulphide residues. The same number of disulphide residues was found by direct measurement. Three to six fewer thiol groups were found in preparations made in the absence of dithiothreitol. The missing residues were accounted for as cysteic acid. The distribution of disulphide bonds and of exposed and buried thiol groups among the tryptic fragments of the molecule was measured after labelling with N-ethyl[(14)C]-maleimide. The disulphides were confined to fragment B (mol.wt. 55000), whereas several thiol groups were present on each of the fragments (A, B, A(1) and A(2)). The kinetics of the reaction of the ATPase with 5,5'-dithiobis-(2-nitrobenzoate) showed that four or five of the thiol groups were unreactive in the absence of detergent and that 13 of the remainder reacted with a single first-order rate constant. In the presence of ATP and Ca(2+) the reaction rate of all but two groups of this class was uniformly decreased. In the presence or absence of ATP and Ca(2+) the rate constant for inactivation was close to the rate constant for this class, but was not identical with it. No selective protection of a specific active-site-thiol group was observed. Parallel experiments with sarcoplasmic reticulum gave similar results, except that the reaction rates were a little lower and there were two more buried groups. Solution of ATPase of sarcoplasmic reticulum in detergent greatly increased the reactivity of all thiol groups. The effects of low concentrations of deoxycholate were reversible. EGTA or low concentrations (0.02mm) of Ca(2+) of Mg(2+) had very little effect on the reactivity.

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The primary structure of the calcium-transporting adenosine triphosphatase of rabbit skeletal sarcoplasmic reticulum. Soluble tryptic peptides from the succinylated carboxymethylated protein.

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