Immunoglobulins of Mice V . the Metabolic ( Catabolic ) Properties of Five

Studies in man (1, 2), rabbit (3), and guinea pig (4) have shown that the 18S 71-macroglobu]ins (IgM) are catabolized much more rapidly than 7S 72-globulins (IgG). Thus, immunoglobulin classes may differ in their rates of turnover. Differences in the catabolic control of immunoglobulins are also discernable. The serum level of 7S 7-globulin (IgG) helps to determine the catabolic rate; the higher the serum level, the greater the catabolic rate (5, 6). 18S 71-macroglobulin (IgM) catabolism, however, appears to be unrelated to the serum 71-macroglobulin level (2). Thus the catabolic properties of all classes of immunoglobulins need to be characterized and the catabolic interrelationships between immunoglobulin classes further defined.