The Loss of Enzyme Activity from Erythroid Cells During Maturation

Abstract

It has been known for over thirty years that the activities of certain “age-dependent” enzymes decline during the circulatory life-span of erythroid cell (1). The kinetics of this decay have usually been assumed to be a simple exponential function, that is, occurring continually throughout the life of the cell. In this view, erythrocyte death was often thought to be determined by one or more critical enzymes decaying to a threshold level that was too low to sustain an adequate metabolic rate. Estimates of enzyme half-lives have been calculated from studies that fractionate erythrocytes into groups of different mean cell density (2,3). Although it is clear that red cell density increases with age, numerous recent studies have shown that there is not a simple correlation between age and density (4,5). This is because the major part of the change in density probably occurs very early in maturation, and there appears to be a substantial range of initial density. Density-fractionation and other in vitro methods are therefore unable to resolve cell preparation into fractions of uniform cell age, and cannot provide an accurate picture of enzyme decay.