EFFECT OF PHOSPHATE RESIDUE OF NADPH ON THE INTERACTION BETWEEN CATALYTIC DOMAINS OF A MULTIFUNCTIONAL POLYKETIDE SYNTHETIC ENZYME 6-HYDROXYMELLEIN SYNTHASE

Association of NADPH with the ketoreducing domain of 6-hydroxymellein synthase, a multifunctional polyketide synthetic enzyme of carrot, evo ked the alternation of microstructure around the primary binding site of the co-substrates acetyl-and malonyl-CoAs, and this resulted in the marked decrease in K-m value of the enzyme protein for acetyl-CoA. Ln contrast, the enzyme did not show the increase in the affinity to the substrate when NADPH was replaced by NADH. These results suggest that the phosphate residue attached to 2'-position of adenosyl moiety of N ADPH molecule plays an important role in the co-operative interaction between these functional domains of the synthase. (C) 1998 Elsevier Sc ience B.V.