Correlation between protein 4.1a/4.1b ratio and erythrocyte life span.

Erythrocyte membranes from various healthy mammals contained a doublet of protein 4.1a and 4.1b, which appeared to differ by 2-3 kDa on sodium dodecyl sulfate polyacrylamide gel electrophoresis. The ratio of protein 4.1a/4.1b showed much variety among animal species, and the 4.1a/4.1b ratio correlated to the mean erythrocyte life span, that is, the mean cell age in circulating blood. We also found that the 4.1b is the predominant form in the immature erythroid cells such as reticulocytes and K562 cells. In addition, the 4.1b but not 4.1a protein was metabolically labeled with [35S]methionine in the erythropoietic cells from anemic mouse. Immunological detection showed that there is a doublet of minor variants of protein 4.1 with apparent molecular masses slightly more than those of 4.1a and 4.1b. The ratio of these minor isoforms designated as 4.1a + and 4.1b + revealed the alteration during erythrocyte senescence as observed in 4.1a/4.1b ratio. These results show that protein 4.1 may be synthesized as 4.1b and 4.1b + and intercalated into membrane skeletons at an early stage of erythroidal differentiation, and that the posttranslational modification into 4.1a and 4.1a + appears to occur by a common mechanism in many mammalian species. Feline erythrocytes, however, appeared to lack such a postsynthetic processing of protein 4.1, and exhibited one major component of 4.1b with the other minor variant of 4.1b +.