Purification and characterization of chlorogenic acid: Chlorogenate caffeoyl transferase in sweet potato roots

Abstract

A chlorogenic acid : chlorogenate caffeoyl transferase, which catalyses the conversion of chlorogenic acid to isochlorogenic acid, has been purified 3600-fold from sweet potato root and characterized. The purified enzyme yielded one band on polyacrylamide gel electrophoresis both under non-denaturing and denaturing conditions. The enzyme was shown to consist of a single polypeptide of molecular weight 25 000 by gel filtration chromatography and SDS-gel electrophoresis. pI of the enzyme was 4.6. The optimum pH of the enzyme reaction was 5.0 (50 % at pH 3.7 and 6.8). The enzyme did not have any cofactor requirements. The enzyme showed a strict substrate specificity toward chlorogenic acid, for which the K m value was 0.87 mM. The enzyme activity changed in a manner indicating its involvement in the conversion of chlorogenic into isochlorogenic acid during incubation of sliced sweet potato root tissues.