Amino acid sequences around the cystine residues in horse growth hormone.
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ABSTRACT:
SUBMITTER: Oliver L
PROVIDER: S-EPMC1186747 | biostudies-other | 1968 Aug
REPOSITORIES: biostudies-other
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Project description:1. A diagonal electrophoretic technique for studying the amino acid sequence around cysteine and cystine residues in proteins is described. The residues are first converted into S-aminoethylcysteine, and the protein is then treated with S-ethyl trifluorothioacetate, which trifluoroacetylates all the protein amino groups. The modified protein is digested enzymically and the resulting peptides are separated by paper electrophoresis. After exposure of the peptides on the paper to ammonia vapour, the electrophoresis is repeated, this time at right angles to the original direction. Peptides from which a trifluoroacetyl group is removed by the ammonia treatment will vacate the 45 degrees diagonal formed by all other unaffected peptides owing to the exposure of an additional amino group and consequent increased electrophoretic mobility towards the cathode. Peptides containing lysine or S-aminoethylcysteine are readily purified by this technique. 2. The successful application of the technique to bovine insulin is described. 3. Various methods for distinguishing peptides containing lysine from those containing S-aminoethylcysteine in more complicated proteins are suggested and discussed.
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Project description:1. The amino acid sequences around three disulphide bridges and four methionine residues of porcine pepsin were studied by using diagonal electrophoresis methods. 2. Two of the three disulphide bridges were in small loops of five and six residues. The sequence around one of the two half-cystine residues of the third disulphide bridge had a large number of acidic residues. 3. The sequence of a tetrapeptide containing phosphoserine was also determined. 4. Four unique methionine-containing sequences were constructed. The information is sufficient for the determination of the overlaps in the cyanogen bromide fragments of pepsin. 5. The usefulness of diagonal methods in the study of protein structure, the relative positions of cystinyl and methionyl residues in porcine pepsin and the homology between pepsin and rennin are discussed.
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Project description:1. Calf lens alpha-crystallin was carboxymethylated with radioactive sodium iodoacetate to label the thiol group. 2. The protein was then digested with trypsin or alternatively fractionated in urea to obtain the acidic (A) chains, which were then digested with trypsin. Either procedure gave two radioactive peptides containing carboxymethylcysteine. 3. These two peptides were closely related: the longer form contained 28 amino acid residues, and the shorter lacked two residues at the N-terminal end of the longer form. 4. The amino acid sequence of the peptides have been determined. 5. No evidence for the presence of more than one cysteine residue/chain was found. 6. The question of the molecular weight of the chains is discussed.
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