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UDP‐glucose pyrophosphorylase from the plant fraction of nitrogen‐fixing soybean nodules
Author(s) -
Vella John,
Copeland Les
Publication year - 1990
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1990.tb08728.x
Subject(s) - pyrophosphate , enzyme , divalent , chemistry , biochemistry , glycine , sodium , phosphate , d glucose , chromatography , amino acid , organic chemistry
UDP‐glucose pyrophosphorylase (EC 2.7.7.9) has been highly purified from the plant fraction of soybean ( Glycine max L. Merr. cv Williams) nodules. The purified enzyme gave a single polypeptide band following sodium docecyl sulphate polyacryla‐mide gel electrophoresis, but was resolved into three bands of activity in non‐denaturing gels. The enzyme appeared to be a monomer of molecular weight between 30 and 40 kDa. UDP‐glucose pyrophosphorylase had optimum activity at pH 8.5 and displayed typical hyperbolic kinetics. The enzyme had a requirement for divalent metal ions, and was highly specific for the substrates pyrophosphate and UDP‐glucose in the pyrophosphorolysis direction, and glucose‐1‐phosphate and UTP in the direction of UDP‐glucose synthesis. The K m values were 0.19 m M and 0.07 m M for pyrophosphate and UDP‐glucose, respectively, and 0.23 m M and 0.11 m M for glucose‐1‐phosphate and UTP. The maximum velocity in the pyrophosphorolysis direction was almost double that for the reverse reaction. UDP‐glucose pyrophosphorylase did not appear to be subject to a high degree of fine control, and activity in vivo may be regulated mainly by the availability of the substrates.