Adenylate cyclase of human parathyroid gland

Experiments were performed on a particulate fraction from human parathyroid glands. A high activity of adenylate cyclase was detected which was linear with time and protein concentration. The enzyme had an optimum pH in the range of 7-8 and a Km for ATP of 0.44 × 10^–3 M. Ca⁺⁺ had a profound inhibitory effect; a concentration of 0.5 mM Ca⁺⁺ reduced enzyme activity by 60%. Maximal enzyme activity was obtained with 5 mM Mg⁺⁺; higher concentrations of this cation also inhibited enzyme activity. The effect of Mn⁺⁺ was similar to that of Mg⁺⁺. Enzyme activity was stimulated by NaF, catecholamines, glucagon, and calcitonin. The effect of catecholamines seems to be mediated through β-adrenergic receptors.