Regulation of C4 photosynthesis: modulation of mitochondrial NAD-malic enzyme by adenylates.

Effects of adenylates on the activity of mitochondrial NAD-malic enzyme from NAD-malic-enzyme (NAD-ME)-type and phosphoenolpyruvate-carboxykinase-(PKC)-type C4 plants are examined. At physiological concentrations, ATP, ADP, and AMP all inhibit the enzyme from Atriplex spongiosa and Panicum miliaceum (NAD-ME-type plants), with ATP the most inhibitory species. The degree of inhibition is greater with subsaturating levels of activator, malate, and Mn2+. NAD-malic enzyme from Urochloa panicoides (PCK-type) is activated by ATP (up to 10-fold) and inhibited by ADP and AMP. These effects are discussed in relation to regulation of C4 photosynthesis.