Selective fission of proteins

Black, John Alexander (1964) Selective fission of proteins. PhD thesis, University of Glasgow.

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Abstract

Cyanogen bromide is known to be a chemical agent which causes selective fission at mothionyl bonds in proteins under mild acid conditions and at room temperature. Its action on three proteins, horse-heart cytochrome c, horse-heart, myoglobin and bovine serum albumin, is studied by separation of the reaction products by means of gel filtration, followed by their amino acid analysis, and in the case of bovine serum albumin, tryptic digestion and fingerprinting. Cytochrome c, which contains two methionine residue yielded three peptides, two of which correspond to the fragments expected from the published sequence and are formed by fission of the peptide chain at both methionine reside. The other appears to resulto from fission at one methionine locus, that nearest the C-terminus of the peptide chain. A fourth peptide should bee-present in the reaction products as a result of complete fission and although evidence is given for its existence it has not been isolated. Myoglobin, also containing two methionine residues, gave our peptides, three of which account for all the amino acid residues in myoglobin and are therefore the products, of complete fission. The fourth peptide accounted for by non cleavage of the methionyl bond joining two of the previous three peptides in the intact protein. N-terminal alalyses of the four peptides allow the three peptides obtained by complete fission to be placed in the order of their appearance in the intact protein. From its methionine content of four, bovine serum albumin was expected to give five fragments. Initial separations on Sephadex G 75 indicated the presence of this number of components in the reaction mixture. However improved separations on coupled columns of Sephadex G 200 and G 75 suggest that fifteen to twenty components are present, indicating incomplete cleavage at each of the four methionine residues of albumin. From the latter separation, three fractions have been isolated which account fear' the amino acid composition and tryptic peptides of the complete protein. Two of the fractions appear to contain pure peptides of calculated molecular weights 20,000 and 15,000. From the amino acid composition, tryptic peptides and gel filtration behaviour of the third fraction, it appears to contain three peptides of approximate molecular weight, 10,000. Cyanogen bromide treatment of partially reduced albumin gave a slightly simpler mixture of products from which a new peptide of calculated molecular weight, 12,000, was isolated. Fingerprinting results suggest that it is one of the peptides present in the previous fraction containing three components. Evidence has also been obtained from fingerprinting for the existence of two of these components joined together in a single polypeptide chain.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: G Leaf
Keywords: Molecular biology, Biochemistry
Date of Award: 1964
Depositing User: Enlighten Team
Unique ID: glathesis:1964-73972
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 14 Jun 2019 08:56
Last Modified: 14 Jun 2019 08:56
URI: http://theses.gla.ac.uk/id/eprint/73972

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