SITE-SPECIFIC REGULATORY INTERACTION BETWEEN SPINACH LEAF SUCROSE-PHOSPHATE SYNTHASE AND 14-3-3-PROTEINS

We report an Mg2+-dependent interaction between spinach leaf sucrose-p hosphate synthase (SPS) and endogenous 14-3-3 proteins? as evidenced b y co-elution during gel filtration and co-immunoprecipitation. The con tent of 13-3-3s associated with an SPS immunoprecipitate was inversely related to activity, and was specifically reduced when tissue was pre treated with 5-aminoimidazole-4-carboxamide riboside, suggesting metab olite control in vivo. A synthetic phosphopeptide based on Ser-229 was shown by surface plasmon resonance to bind a recombinant plant 14-3-3 , and addition of the phosphorylated SPS-229 peptide was found to stim ulate the SPS activity of an SPS:14-3-3 complex, Taken together, the r esults suggest a regulatory interaction of 14-3-3 proteins with Ser-22 9 of SPS, (C) 1998 Federation of European Biochemical Societies.