ENZYME SYSTEMS OF THE ERYTHROCYTE 513 



some cases, the surviving donor cell count fell linearly when plotted 

 against time, while in other cases an initial period of rather more 

 rapid destruction was observed, after which the decay was linear. 

 The linear decay leads to a value of about 120 days for the true 

 average life of the erythrocyte. In their earlier work, these authors 

 measured the decay in a number of anemias and found that in some 

 it was linear while in others there was a more rapid decay in which 

 the donor cell count fell exponentially. 



Where a linear mortality curve is obtained, the destruction of the 

 erythrocytes must depend primarily on some characteristic of the 

 erythrocyte, which reaches a critical value after a certain period. 

 Where the factor responsible for hemolysis affects cells irrespective 

 of their age, the decay curve will have an exponential component as 

 well as a linear component. Hemolytic mechanisms (discussed in 

 Section 6.) are of this type, as would be a mechanism dependent on 

 the mechanical fragmentation of cells in the circulation. Since the 

 normal breakdown is not exponential, the rate-determining factor 

 must be sought in some characteristic of the aged cell, while factors 

 external to this can only be secondary. 



If this conception is correct, it is clearly inadequate to view the 

 erythrocyte simply as a dying cell. It must be looked on as a special 

 cell which is able to live for about 120 days without a nucleus, at 

 the end of which time it enters a stage in which it dies relatively 

 rapidly. Callender, Powell, and Witts (395) are not able to attach 

 a numerical value to the variation between the life of one cell and 

 another, but they conclude, in agreement with Schi^dt {2IfJ^2), that 

 most cells are destroyed within a few days of their average life span. 

 Shemin and Rittenberg {25J^3) found 50% to live 127 ± 7 days. 



3. ENZYME SYSTEMS OF THE ERYTHROCYTE 



3.1. Origin and Possible Function 



In view of the evidence given in the previous section' that the lifetime 

 of the erythrocyte is primarily controlled by some internal process, it becomes 

 of great interest to try to identifj' the system or systems responsible. At 

 the present stage of knowledge it is not possible to carry such an analysis 

 much further than to suggest a number of avenues for further work, but 

 since the problem appears to be closely linked with the preservation of 

 functional hemoglobin within the cell, it appears desirable to make such 

 an attempt. 



Although the mature mammalian erythrocyte has been shown to contain 



