Some kinetic and chromatographic properties of detergent-dispersed adenylate cyclase

Studies on the reaction kinetics and chromatographic properties of detergent-dispersed adenylate cyclase are described. Detergent-dispersed enzyme was prepared from whole rat cerebellum and from partially purified plasma membranes from rat liver. Data were simulated to fit kinetic models for which an inhibitor is added in constant proportion to the variable substrate. Models were chosen to distinguish whether the adenylate cyclase reaction may be controlled by an inhibitory action of free ATP--4 (or HATP--3) or by a stimulatory action of free divalent cations. The various kinetic models were then tested with the dispersed brain adenylate cyclase with both Mg++ and Mn++ and in two different buffer systems. The experimental data indicate that this enzyme has a distinct cation binding site, but exhibits no significant inhibition by HATP--3 or ATP--4. The detergent-dispersed adenylate cyclase both from liver plasma membranes and from brain have been chromatographed on anion exchange material and have been subjected to gel filtration. The presence of detergent was required for elution of cyclase activity from DEAE-Sephadex but was not required when DEAE-agarose was used. Dispersed brain cyclase was also chromatographed on agarose-NH(CH2)3NH(CH2)3-NH2 which exhibits both ionic and hydrophobic properties. Fifty percent of the applied activity was recovered with a fivefold increase in specific activity. The data suggest that the relative effectiveness of a given chromatographic procedure for detergent-dispersed adenylate cyclase may reflect the influence of both hydrophobic and ionic factors.