J. Amir, J.,Preiss

The biochemical work on the enzyme involved in starch-to-sugar conversion was continued during a sabbatical year at the Dept. of

Biochemistry and Biophysics, University of California at Davis. In

cooperation with Prof. Preiss, we studies the kinetics and properties of leaf

sucrose-phosphate synthase. The principal results obtained were:

a) Sucrose-P-phosphate synthase is an important regulatory enzyme,modulated by the fructose-6-P /Pi and UDP glucose/Pi ratios in the cellcytoplasm.

b) Of particular interest was the inhibition of the leaf sucrose-P-syuthase by (pyrophosphate (Pi). This inhibitory is quite effective in the range 5 to 10mM.

c) The inhibitor is competitive with UDP glucose, and it also slightly decreases the apparent affinity for the fructose-6-P as the substrate S0.5 value (concentration of substrate giving 50% of maximal velocity,

increased from 3.0 to 5.9 mM).

Amir, J. and Preiss, J. (1982). The kinetic characterization of spinach leaf sucrose-phosphate synthetase. Plant Physiol. 69: 1027-1030.