T: An increase in apparent affinity for sucrose of Mung Bean sucrose synthase is caused by in vitro phosphorylation or directed mutagenesis of Ser. Plant Cell Physiol 1998, 39:1337–1341. PLoS One 2012

A mutational analysis of mung bean (Vigna radiata Wilczek) sucrose synthase was performed by site-directed mutagenesis of the recombinant protein expressed in Esche-richia coli, in which two different acidic amino acid resi-dues (Asp or Glu) were introduced at Ser11 (S11D, SHE). Only the wild-type enzyme (Ser11) was phosphorylated in vitro by a Ca2+-dependent protein kinase from soybean root nodules, suggesting that this is the specific target resi-due in mung bean sucrose synthase. The apparent affinity for sucrose was increased in this phosphorylated enzyme and also in the S11D and SHE mutant enzymes, although the affinities for UDP-glucose and fructose were similar in the wild-type, phosphorylated wild-type, and mutant en-zymes. These results suggest that a monoanionic (1~) side chain at position 11 mimics the Ser"-P2 ~ residue to bin