Studies on the biosynthesis of ovalbumin.

Linderstrplm-Lang and Ottesen have reported the discovery of a bacterial enzyme which brings about the transformation of ovalbumin to a new, easily crystallizable protein, plakalbumin. Unlike other proteolytic processes, this reaction seems to involve the rupture of a limited number of peptide bonds, with the release of only slightly over 1 per cent of the total ovalbumin nitrogen (1, 2). Villee, Linderstrom-Lang, and Ottesen report that this nitrogen corresponds to 6 amino acid residues (3 alanine, 1 glycine, 1 valine, 1 aspartic acid) which appear as a “hexapeptide” and its split-products (3).’ In the present experiments this proteolytic reaction has been applied to samples of radioactive ovalbumin prepared by the incubation of minced oviduct tissue with C1402 (4). Aspartic acid from the hexapeptide (nonprotein nitrogen) fraction could then be isolated and the specific activity of its carboxyl carbons compared with the average specific activity of all the aspartic acid residues from the plakalbumin fraction. In every case, the specific activity of the hexapeptide aspartic acid residue was much higher than that of the plakalbumin aspartic acid residues (approximately 31 residues (5)). The ratios of these specific activities varied from 1.3 : 1 to 3.5: 1. These data, showing a marked difference in the way in which amino acid residues are introduced into different points in the molecule, might be interpreted as indicating the synthesis of peptide intermediates prior to the biosynthesis of ovalbumin molecules. Other possible interpretations will be discussed in a later section.