Characterization of adenylate kinase in intact mitochondria of fertile and male sterile potato (Solanum tuberosum L)

Adenylate kinase (AK) (E.C. 2.7.4.3) plays a central role in adenylate metabolism, catalyzing the conversion of two ADP to AMP and ATP and vice versa. The true substrates of the mitochondrial enzyme from Solanum tuberosum were determined to be ADP and MgADP (forward reaction), and AMP and MgATP (reverse reaction). A sequential random kinetic mechanism is proposed for AK from mitochondria. The apparent K-mS values of AK in intact mitochondria were 3 mu M and 53 mu M for ADP and MgADP, respectively (forward reaction), and 33 mu M and 59 mu M for AMP and MgATP, respectively (reverse reaction). K-mS values of AK from male fertile and male sterile lines of Solanum tuberosum were similar. When Ap(5)A (an inhibitor of AK) was added to isolated mitochondria with no substrate for the electron transport chain, ATP formation from ADP stopped completely, due to an adenylate kinase activity. Both high levels of magnesium and no magnesium in the test medium, prevented AK activity because of lack of free ADP and MgADP, respectively (forward reaction).