Purification and Properties of ent-Kaurene Synthase B from Immature Seeds of Pumpkin

Abstract

ent-Kaurene synthase B (KSB) was purified 291-fold from a crude enzyme preparation from endosperm of pumpkin (Cucurbita maxima L.). Separation of ent-kaurene synthase A and KSB was achieved by hydrophobic interaction chromatography. The fractions containing KSB activity were further purified by diethylaminoethyl, phenyl, and hydroxyapatite column chromatography. Using sodium dodecyl phosphate-polyacrylamide gel electrophoresis, the purest enzyme preparation showed a major band at an apparent molecular mass of 81 kD. The amount of protein in this band was correlated with KSB activity after diethylaminoethyl and hydroxyapatite chromatography. The N terminus of the 81-kD protein was blocked. Therefore, the protein was partially digested with protease and the amino acid sequences of the resulting major peptide fragments were analyzed. A polyclonal antibody was raised against a synthetic peptide based on the longest peptide fragment combined with a keyhole limpet hemocyanin. The antibody recognized only the 81-kD denatured protein and not the native KSB. The properties of KSB were examined using the phenyl-purified enzyme preparation. The Km value for copalyl pyrophosphate was 0.35 [mu]M, and the optimal pH was 6.8 to 7.5. The KSB activity required divalent cations such as Mg2+, Mn2+, and Co2+, whereas Cu2+, Ca2+, and Ba2+ inhibited the activity.