PLANT PHYSIOLOGY , Vol 115, Issue 1 223-227, Copyright © 1997 by American Society of Plant Biologists
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BIOCHEMISTRY AND ENZYMOLOGY |
Physical and Kinetic Evidence for an Association between Sucrose-Phosphate Synthase and Sucrose-Phosphate Phosphatase
E. Echeverria, M. E. Salvucci, P. Gonzalez, G. Paris and G. Salerno
University of Florida, Citrus Research and Education Center, 700 Experiment Station Road, Lake Alfred, Florida 33850 (E.E., P.G.)
The possible formation of a multienzyme complex between sucrose
(Suc)-phosphate synthase (SPS) and Suc-phosphate phosphatase (SPP) was
examined by measuring the rates of Suc-6-phosphate (Suc-6-P) synthesis and
hydrolysis in mixing experiments with partially purified enzymes from
spinach (Spinacia oleracea) and rice (Oryza sativa) leaves. The addition of
SPP to SPS stimulated the rate of Suc-6-P synthesis. SPS inhibited the
hydrolysis of exogenous Suc-6-P by SPP when added in the absence of its
substrate (i.e. UDP-glucose) but stimulated SPP activity when the SPS
substrates were present and used to generate Suc-6-P directly in the
reaction. Results from isotope-dilution experiments suggest that Suc-6-P
was channeled between SPS and SPP. A portion of the SPS activity comigrated
with SPP during native polyacrylamide gel electrophoresis, providing
physical evidence for an enzyme-enzyme interaction. Taken together, these
results strongly suggest that SPS and SPP associate to form a multienzyme
complex.
