514 Xr. HEMOGLOBIN CATABOLISM, I 



some nuclear material {2oG0), its capacity, in the absence of a nucleus, for 

 synthesis of new enzymes is probably very low and the biochemical repairs 

 must be carried on by enzymes inherited from the more immature cell. 

 Since the structure of the cell cannot be considered as static, its maintenance 

 during life must involve an expenditure of energy together with the provi- 

 sion of the necessary metabolites. In view of the selective permeability 

 of the cell wall some of these may have been accumulated during an earlier 

 stage in development. Although the cell contains proteins, lipides, and carbo- 

 hydrates, evidence that it contains enzymes connected with the metabolism 

 of the first two types of substances is lacking. Although ketone bodies and 

 amino acids may be found in the cell, they appear to be accumulated in 

 the mature cell only in a passive fashion, determined by the permeabilitj^ 

 of the cell wall. 



The function of those enzymes which have been found in the erythrocyte 

 has been elucidated only in a few cases, such as carbonic anhydrase and some 

 of the enzymes concerned with the reduction of hem/globin. In other cases, 

 such as catalase or true choline esterase, the reactions which are catalyzed 

 may be well known, but the biological function in the cell is not yet clear. 

 Finally, the copper protein which Keilin and Mann isolated in a crystalline 

 form has not yet been shown to possess any catalytic power. Some of these 

 substances, indeed, may be of little importance in the physiology of the 

 mature cell, being merely relics from the reactions carried out in the immature 

 cell (c/. 1020). 



3.2. Carbohydrate Metabolism of the Erythrocyte 



The physiological importance of the reducing systems in the erythrocyte 

 was clearly demonstrated by the classic experiments of Haldane, Makgill, 

 and Mavrogordato (1104) in 1897 on the reduction of hem/globin in vivo 

 {cf. Section 4). The actual systems involved were little investigated until 

 Barron and Harrop {185,1137) observed the increased respiration of the 

 mammalian erythrocyte in the presence of methylene blue and glucose. 



In the absence of substances capable of inducing an acceptor respiration, 

 the oxygen uptake of the mammalian erythrocyte is small. Ramsey and 

 Warren {2201), after allowing for the relatively much greater respiration of 

 reticulocytes, arrived at a figure for rabbit cells of 8 /xl. of oxygen per gram 

 of moist cells per hour, while a figure of about twice this may be derived 

 from the experiments of Jacobsen and Plum {I4OO). The respiration may be 

 inhibited by carbon monoxide {294-0,2942) and by lowering the oxygen pres- 

 sure. Kempner {loll) found, however, that the respiration of human 

 erythrocytes remained uninhibited down to a concentration of 4% oxygen 

 in the gas phase, while the respiration of nucleated avian erythrocytes was 

 40% inhibited under the same conditions. This may indicate either an 

 unsaturation of the oxidase by hydrogen-transporting enzymes in the case 

 of the nonnucleated cells, whose respiration is much less than that of avian 

 cells, or the oxidase in the former cell may have a much greater affinity for 

 oxygen than that of the latter. 



There is, however, little evidence that the mature mammalian erythrocyte 

 contains any cytochrome oxidase at all. The evidence apparently rests on 



