Figure 1

Bubble graph showing the correlation between protein Band 4.1a/4.1b ratio and RBC life span in a number of mammals. Band 4.1 protein, whose modification from the naturally synthesized ‘4.1b’ form to the ‘4.1a’ form trough deamidation of a single asparaginyl residue, can be regarded as a molecular clock.⁶ The mean 4.1a/4.1b ratio of the total population of circulating RBCs from a given animal was plotted against the mean erythrocyte survival time of that animal. The 4.1a/4.1b values were originally measured by the authors of the article from which these data were derived;¹³ the S.D. was omitted for the sake of clarity, but it can be found in the original article. In the case of the cat, the expressed protein 4.1b does not undergo conversion to 4.1a because Ser, not Asn is present at position 502 (the deamidating Asn in protein 4.1 in humans and other mammals). Therefore, 4.1a/4.1b ratio cannot be measured in cat RBCs. The survival time is given as mean of two or more values obtained in the literature, as reported in the above-cited article. It must be reminded that the mean life span of RBCs results from two different kinetics of clearance: a first-order random destruction and a time-dependent destruction. In various mammals, the two components are present to a variable extent with a prevalent time-dependent clearance in human RBCs and an almost complete random clearance in mice. Although information on this aspect is sparse in the literature, the data from the last most accurate comparative account of RBC life span have been used to give an estimate of this aspect. Thus, the entity of the random component of RBC clearance, in % of RBCs removed per day, is given, where available, as the value to the right of the species’ name, which is also reflected in the size of the bubble (data of random destruction taken from Vacha¹⁴)