In Vitro Biosynthesis of Homogalacturonan by a Membrane-bound Galacturonosyltransferase from Epicotyls of Azuki Bean(Biochemistry & Molecular Biology)

概要

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A membrane preparation of 7-d-old seedlings from azuki bean (Vigna anguiaris) contained galacturonosyltransferase (GalAT) capable of transferring galacturonic acid (GalA) from UDP-GalA into polygalacturonic acid (PGA) as an exogenous acceptor. The enzyme was maximally active at pH 6.8-7.8 and 25-35℃ in the presence of 5 μM Mn^<2+> and 0.5% (w/v) Triton X-100. Acid-soluble low-M_r (average M_r 10,000) PGA was a more efficient acceptor substrate than acidinsoluble polymer (M_r 70,000). The apparent Michaelis constants for UDP-GalA and low-M_r PGA were 0.14 mM and 0.02 mg/ml, respectively. Various pectins with different degrees of methyl-esterification (DE) were poor acceptors, and the enzyme activity tended to decrease with decreasing DE of the pectins. The transfer products from incubation of the enzyme with UDP-^<14>C-GalA and the low-M_r PGA yielded ^<14>C-GalA_2 as the major product upon digestion with an endopolygalacturonase (EPGase), confirming the incorporation of GalA into PGA through contiguous α-1,4-linkages.
社団法人日本農芸化学会の論文
2001-07-23