The comparative biochemistry of avian egg white proteins.

The homologous proteins from the egg whites of different avian species offer excellent opportunities for the study of the comparative and genetic biochemistry of proteins. Comparative studies of avian egg whites have utilized electrophoretic (l-4), immunological (5, 6), and specific biochemical (7, 8) analyses. These studies have all shown significant, and in some instances large, differences between the whites from eggs of different avian species. The principal and more extensive studies, however, have relied on electrophoretic examinations of the whites (l-3). Although these have supplied distinctive patterns which have been valuable in considering genetic aspects, in many cases they are difficult to interpret in terms of the recognized constituents of chicken egg white. The present study was initiated for the purpose of obtaining more specific biochemical and chemical information on the constituents of the egg whites of a variety of avian species. The specific biochemical and chemical analyses which have been developed for chicken egg white (9, 10) have been employed. These analyses provide information on the presence and relative amounts of the biological activities and chemical groups as found in chicken egg white. They thus give information which is not provided by electrophoretic analyses. In addition, certain of the whites have been fractionated and the purified constituents have been partially characterized. Data have been obtained on the following constituents: ovalbumin, conalbumin, ovomucoid, lysozyme, flavoprotein-apoprotein, sulfhydryl groups, and sialic acid. Important differences have been found for all constituents. The ovomucoids (inhibitors of proteolytic enzymes) were found to exhibit complex differences, varying both quantitatively and qualitatively in their activities, and have been recently described elsewhere (11).