EFFECT OF NADPH-ASSOCIATED KETO-REDUCING DOMAIN ON SUBSTRATE ENTRY INTO 6-HYDROXYMELLEIN SYNTHASE, A MULTIFUNCTIONAL POLYKETIDE SYNTHETIC ENZYME INVOLVED IN PHYTOALEXIN BIOSYNTHESIS IN CARROT
F. Kurosaki, EFFECT OF NADPH-ASSOCIATED KETO-REDUCING DOMAIN ON SUBSTRATE ENTRY INTO 6-HYDROXYMELLEIN SYNTHASE, A MULTIFUNCTIONAL POLYKETIDE SYNTHETIC ENZYME INVOLVED IN PHYTOALEXIN BIOSYNTHESIS IN CARROT, Archives of biochemistry and biophysics, 328(1), 1996, pp. 213-217
6-Hydroxymellein synthase is a polyketide biosynthetic enzyme induced
in carrot cells which is organized as a homodimer composed of multifun
ctional subunits. The synthase liberates triacetic acid lactone, inste
ad of 6-hydroxymellein, as a derailment product when the keto-reducing
reaction at the triketide intermediate stage is interrupted, However,
the efficiency of the triacetic acid lactone-forming reactions is mar
kedly lower than that of the normal reaction, and the kinetic analyses
have revealed that the affinity of the enzyme protein for acetyl-CoA
is appreciably reduced in the abnormal reactions, It is assumed that t
he interaction of the NADPH-associated keto-reducing domain with a put
ative primary binding site(s) of the acyl-CoA in the enzyme structure
affects the entry of the starter unit into the protein. The present fi
nding should provide an example of the novel class of ''subunit commun
ication'' of multimer enzymes, (C) 1996 Academic Press, Inc.