THE SEQUENCE IMMUNOLOGY CORRELATION REVISITED - DATA FOR CETACEAN MYOGLOBINS AND MAMMALIAN LYSOZYMES

Quantitative microcomplement fixation tests employing rabbit antisera were done to compare immunologically 13 cetacean myoglobins and 15 mam malian lysozymes c of known amino acid sequence. In both cases there w as a strong correlation between immunological distance (y) and percent sequence difference (x), as had been found for several other globular proteins. For myoglobin the relationship could be described by y = 10 .5x and for lysozyme by y = 8.5x. The coefficients in both of these eq uations are appreciably higher than the values of 5.1-6.9 reported for three other vertebrate globular proteins (bird lysozyme c, mammalian ribonuclease, and mammalian serum albumin), and they imply that rabbit antisera to mammalian myoglobins and lysozymes are more sensitive to evolutionary substitutions. A strong inverse correlation (r = -0.95) w as found when the slope of the line relating y to x for these five dat a sets was plotted against the percent sequence difference between the rabbit's own protein and the proteins immunized with. Specifically, t he cetacean myoglobins on average differ in amino acid sequence from r abbit myoglobin by less than 13% and exhibit the steepest slope (10.5) , while bird lysozyme sequences differ by nearly 40% from rabbit lysoz yme and exhibit the shallowest slope (5.1).