Orientation and reactivity of NADH kinase in proteoliposomes

NADH kinase was reconstituted in liposomes by employing phosphatidylcholine and phosphatidylethanolamine with n-octyl-beta-D-thioglucoside as a detergent. An analogous molecular organization of the NADH kinase to that in the mitochondrial inner membrane was ascertained to exist in the liposomal membrane. Michaelis constants for NADH and ATP were determined as 27 and 133 microM, respectively. Both values were lower than that of the solubilized enzyme. The catalytic center of NADH kinase was exposed on the outer surface of the reconstituted liposomes. The NADH kinase reconstituted with ADP/ATP carrier protein catalyzed the phosphorylation of exogenously supplied NADH by the use of ATP entrapped in the liposomal matrix.