DECAY PATTERN OF RABBIT ERYTHROCYTE HEXOKINASE IN CELL AGING

During rabbit red blood cell aging glucose phosphorylating activities show several modifications. In the 1st period of the red cell life span the predominant form is similar to hexokinase II, while in the mature erythrocyte the predominant glucose phosphorylating activity resembles hexokinase I. In the oldest cells glucose phosphorylating activity has a low affinity (high Km) for glucose. The modifications of hexokinase in cell aging were studied in vivo in a young erythrocyte population synchronized by actinomycin D, and in vitro in red cells separated in fractions according to different ages. Since protein synthesis is lacking in the mature red cell, the presence of low-affinity hexokinase activity in the oldest erythrocytes may be explained as an age-dependent transformation of a primary hexokinase.