Guanylate cyclase activity of human lymphocytes from peripheral blood, thymus, and tonsils. A comparative study

The subcellular repartition and the distinctive properties of guanylate cyclase (EC 4.6.1.2) vary according to the lymphocyte population studied and according to the presence of detergent. Guanylate cyclase of non-adherent peripheral lymphocytes and of thymus lymphocytes is recovered by more than 90% in the soluble fraction of the homogenate. Kinetics according to the substrate (5'-GTP-Mn2+) is Michaelian, the Ca2+ ion acts as an activator, especially in the case of blood lymphocytes, and the detergent has no effect on the enzyme activity. On the other hand, the guanylate cyclase of tonsil lymphocytes reside in the particulate fraction. It has non-Michaelian kinetics for the substrate, a strong stimulating effect of detergent, and an inhibitory effect of Ca2+. A comparison of the enzymatic activities of unseparated and of non-adherent tonsil lymphocytes obtained from the same donor points to a correlation between their T and B properties: predominant soluble activity in the T population and particulate guanyl cyclase activity in the B subset.