PLANT PHYSIOLOGY , Vol 115, Issue 4 1733-1733, Copyright © 1997 by American Society of Plant Biologists
Correction
R. Gallois, J. C. Prevot, A. Clement and J. L. Jacob
Phosphoribosylpyrophosphate synthetase (PRS; EC 2.7.6.1) from Hevea
brasiliensis Mull. Arg. latex was located in the cytosol. After
purification, its apparent molecular weight under nondenaturing conditions
was estimated at 200,000 [plus or minus] 10,000; a single band at 57,000
[plus or minus] 3,000 was detected after sodium dodecyl
sulfate-polyacrylamide gel electrophoresis. The enzyme seemed to be a
homotetramer. Its affinity constants were estimated at 200 [plus or minus]
30 [mu]M for adenosine triphosphate and 40 [plus or minus] 2 [mu]M for
ribose-5-phosphate. The purified enzyme proved to be functional in a
paraphysiological medium (cytosol deproteinized by ultrafiltration).
Optimum pH was 7.5 in buffer and 6.5 in a paraphysiological medium. No PRS
activity was detected in the absence of the Mg2+ ion. Of the numerous
compounds tested, only Mn2+, phosphoribosylpyrophosphate and inorganic
phosphate affected the enzymatic reaction. Mn2+ (inhibitor constant = 20
[mu]M) and phosphoribosylpyrophosphate (inhibitor constant = 30 [mu]M) were
inhibitors. PRS responded allosterically (Hill's coefficient = 2.3) to
ribose-5-phosphate in the presence of a physiological concentration of
inorganic phosphate (10 mM). These results are set in the physiological
context of laticifers.
