The decline of catalytic enzyme activity concentration of in vivo ageing erythrocytes of the man, the dog and the rat. Approach to a quantitative diagnostic enzymology, IV. Communication.

Human, dog and rat erythrocytes were separated by centrifugation on a discontinuous buffered Percoll gradient into fractions of progressively increasing mean cell age to measure the in vivo decline in catalytic activity of eleven enzymes during the erythrocyte lifespan. Erythrocyte enzymes decline exponentially at different rates and also differ between the species. The maximal and minimal catalytic activities (erythrocyte catalytic activity at the beginning and at the end of the appropriate erythrocyte life-span for a given species) and the intracellular half-life of enzymes estimated. To test the hypothesis that circulating erythrocytes make a significant contribution to the normal catalytic activity in plasma it was assumed as a working hypothesis that the measured loss of catalytic activity in ageing erythrocytes is equivalent to the amount of the enzymes released in catalytically active form into plasma. This contribution was calculated.