Exponential decay of cytochrome b5 and cytochrome b5 reductase during senescence of erythrocytes: relation to the increased methemoglobin content.

Human erythrocytes were divided into age groups according to their density using phthalate esters as separating liquids. The concentration of cytochrome b5 and the activity of NADH-cytochrome b5 reductase decreased exponentially with the age of red cells. The apparent half-life of cytochrome b5 was estimated to be 44 days. The decline of cytochrome b5 seemed to be more rapid than the decline in the activities of glutamate-oxaloacetate transaminase and NADH-cytochrome b5 reductase whose apparent half-lives were 210 and 240 days, respectively. A biphasic decline of cytochrome b5 was observed on storage of erythrocytes at 4 degrees C. It was deduced from the kinetic results that the decrease of cytochrome b5 might be involved in the increase of the concentration of methemoglobin in senescent erythrocytes. Cytochrome b5 may be used as an indicator of mean red cell age.