The primary structure of hen ovalbumin

• Main Author: Nisbet, Andrew D.
• Published: University of Aberdeen 1979
• Subjects: 572.6
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.467175

Evidence for the complete sequence of hen ovalbumin is presented, including previous sequence results obtained after digestion of ovalbumin with trypsin and pepsin. Digestion of ovalbumin with cyanogen bromide, chymotrypsin and staphylococcal protease was necessary to allow presentation of evidence for the position of each of the 385 residues. Large peptides were purified by gel filtration in 50% formic acid and ion exchange chromatography in 8M urea. Small peptides were purified on an automated ion exchange system (the peptide analyser) or by high voltage electrophoresis on paper. Subdigestion of peptides was carried out with thermolysin, subtilisin, trypsin and chymotrypsin, followed by purification on electrophoresis. The evidence was generally sound, although two overlaps were not established and a third was positioned by homology with an identical sequence from turkey ovalbumin. In addition, the evidence was poor for three dipeptide sequences in hydrophilic regions (where the manual dansyl-Edman sequence procedure was less successful). Due to cooperation with George Brownlee and colleagues, partial messenger KNA sequences were available towards the end of the project and a complete mRNA sequence (McReynolds et al., 1978) just before completion of the protein sequence. The two sequences are consistent and the overall evidence for the protein sequence is therefore unequivocal. The sequences for hen ovalbumin and mRNA were compared with the sequences of the soluble tryptic peptides of turkey ovalbumin (Moir, 1973). A Unit Evolutionary Period of around five million years was calculated from rates of mutation. Compared with other proteins, this suggests that ovalbumin has a sequence-dependent function. 6. The NH2 terminal part of the sequence, containing six out of seven intron-exon junctions, was found to be considerably more conserved than the COOH-terminal part, which includes no junctions. It was therefore suggested that the presence of intron-exon junctions in a section of gene sequence may be a powerful factor for its conservation.