Association of 5′nucleotidase activity with immature granulocytes in the bone marrow of guinea pigs

Abstract

Bone marrow leukocytes from adult strain 2 guinea pigs were found to have appreciable levels of 5′adenosine monophosphate hydrolytic activity (105 nmole/h/10 6 cells). On the basis of substrate specificity studies, enzyme inhibition studies, and thin-layer chromatographic analysis of the reaction product, the activity is related to 5′nucleotidase (5′N). The enzyme activity was associated with the membrane-enriched particulate fraction of lysed bone marrow cells. The bone marrow cell-associated 5′N activity was consistently very high in all five strains of guinea pigs examined (77–127 nmole/h/10 6 cells) and the range of activity was at least 10-fold greater than that observed for bone marrow cells obtained from mice, rabbits or rats. Furthermore, the bone marrow cell-associated 5′N activity in strain 2 guinea pigs was 5-fold greater than that observed for spleen and at least 13-fold greater than that of blood, mesenteric lymph nodes or thymus obtained from the same animal. Fractionation of strain 2 guinea pig bone marrow cells on Percoll density gradients showed that as the proportion of immature granulocytes increased in the various cell fractions, so did the 5′N activity. The cell fraction that sedimented at a density of 1.071 g/ml had the highest 5′N activity and the majority of the cells (94%) were immature granulocytes. The bone marrow compared to blood and spleen had the highest number of total granulocytes and the highest percentage of immature granulocytes. We conclude that the elevated bone marrow-derived 5′N activity in guinea pigs is associated with the resident population of immature granulocytes in that tissue.