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The activity of inorganic pyrophosphatase (PPase) of red blood cells (rbc) from newborns is about 40% higher than that of adults. To answer the question whether the higher activity was due to the enhanced reticulocyte count of the newborn's cell population, the rbc of both newborns and adults were separated into different density subpopulations by means of isopycnic density gradient centrifugation in dextran. To judge the quality of separation in the individual age populations of rbc, the activity of glucose-6-phosphate dehydrogenase (G-6-PD) and the reticulocyte count were determined. The activity fall of PPase during maturation and aging of rbc is stronger than that of G-6-PD. The density subpopulations of rbc from newborns and adults with equal reticulocyte counts show the same PPase activities yet different G-6-PD activities. Obviously, the higher PPase activity of a cell population of newborns is due to the higher proportion of reticulocytes. The inorganic PPase is well suited as a guiding criterion to judge the maturity and age of rbc of newborns.

A simple system of incubation of reticulocytes with a small degree of haemolysis has been developed. It was possible to test the influence of inorganic phosphate, pH-values in the range of 7.0--9.0 and anaerobic conditions on the in vitro maturation of reticulocytes. As main criteria of the maturation the RNA-content and the activity of PPase has been tested. The decrease of the RNA-content and the activity of the PPase is highly significant during maturation. The decrease of RNA and the reduction of reticulocytes are stimulated by inorganic phosphate.

In leukocytes of exudate from diabetic rabbits, the activities of hexokinase, phosphoglucomutase and glucose-6-phosphate dehydrogenase are increased, and a tendency of adenylate kinase activity to decline is observable. The activities of UDP-pyrophosphatase, UDP-glycogentransferase, 6-phosphogluconate dehydrogenase and glutahione reductase in the exudate erythrocytes in diabetes are not essentially altered. The decrease of the key enzymes of glycolysis and pentose phosphate cycle, providing the leukocytes with energy and metabolites, reduces the functional activity of leukocytes from exudate in diabetes.