A Comparative Electrophoretic Study of Avian Plasma Proteins

relationships has led to the study of many characters. In addition to comparative morphology some systematists have utilized ecology, behavior, serology, and biochemistry as clues to the degrees of genetic relatedness among organisms. Because protein molecules are primary gene products it is logical to assume that comparisons among homologous proteins from different organisms should provide useful systematic data. The rationale behind this approach to systematics has been discussed by several authors including Sibley (1960, 1962, 1964, 1965, 1967), Zuckerkandl and Pauling (1965), and Dessauer (1969). The plasma proteins are an obvious choice for investigation because they are easy to collect and because a great deal is known about their properties and functions. Plasma is the fluid portion of blood in which the blood cells are suspended. It is a complex mixture of proteins, carbohydrates, lipids, steroids, and free ions whose composition varies with sex, age, starvation, season, etc. (Moore 1948; Clegg et al. 1951; Vanstone et al. 1955; Dessauer and Fox 1956; Saito 1957b). The protein constituents of plasma, while often quantitatively variable, usually show a high degree of qualitative species specificity when examined by any standard biochemical technique (Morris and Courtice 1955; Zweig and Crenshaw 1957; Drilhon et al. 1958; Woods et al. 1958; Sulya et al. 1961). Some of these studies were based upon serum, the fluid portion of the plasma which is extruded from a blood clot. Plasma thus contains the blood proteins involved in clotting while serum lacks them. Most of the research on plasma proteins has dealt with human material although there has been a great deal of work on other mammalian species and the domestic fowl, Gallus gallus. The major protein components of plasma are albumin, the alpha-, beta-, and gamma-globulins, and various subfractions thereof. The nomenclature of the various components is usually determined by their electrophoretic mobilities with reference to normal human plasma. Thus, albumin is the fastest fraction, alpha-globulin the next fastest and gammaglobulin the slowest. The identification of plasma proteins under different conditions can be difficult (Espinosa 1961; Beaton et al. 1961). Up to 70 different proteins have been found in normal human plasma (Dessauer and Fox 1964) while Baker et al. (1966) found 40 electrophoretic bands in pheasant serum, 14 of which were identifiable. The review by Putnam (1960) provides information on the chemical composition of plasma. In paper electrophoresis at pH 8.6 the fastest c mponent in human plasma is albumin. It has a molecular weight of about 69,000 and is is electric at pH 4.7 (Phelps and Putnam 1960). It may be assumed that the values for other mammals and for birds are similar (Phelps and Putnam 1960:169). Plasma albumin has the same chemical properties as alpha livetin of egg yolk (Williams 1962a) but it has no known specific biological functions (Foster 1960). There are several alpha-globulins, which presumably have different functions. The best known are the hemoglobin-binding haptoglobins and the copper-binding ceruloplasmin. Human haptoglobin has a molecular weight of 85,000 and it is isoelectric at pH 4.1, while ceruloplasmin has a molecular weight of 151,000 and is isoelectric at pH 4.4 (Phelps and Putnam 1960). There are several discrete beta-globulins, most of which have unknown functions. The best known of these are the transferrins. Tra sferrin, also called siderophilin, is an ironbinding protein with a molecular weight of approximately 90,000; it is isoelectric at pH 5.9 (Phelps and Putnam 1960). It has been found that the protein moiety of the transferrin molecule is identical to that of the conalbumin of egg white. They differ only in their 1 Present address: Department of Biology, University of North Carolina at Greensboro, Greensboro, North Carolina 27412.