INVESTIGADORES
GONZALEZ Daniel Hector
artículos
Título:
Interaction of acetyl phosphate and carbamyl phosphate with plant phosphoenolpyruvate carboxylase
Autor/es:
GONZALEZ, DANIEL H.; IGLESIAS, ALBERTO A.; ANDREO, CARLOS S.
Revista:
BIOCHEMICAL JOURNAL
Editorial:
PORTLAND PRESS LTD
Referencias:
Año: 1987 vol. 241 p. 543 - 548
ISSN:
0264-6021
Resumen:
Acetyl phosphate produced an increase in the maximum velocity (Vmax. for
the carboxylation of phosphoenolpyruvate catalysed by
phosphoenolpyruvate carboxylase. The limiting Vmax. was 22.2 mumol X
min-1 X mg-1 (185% of the value without acetyl phosphate). This compound
also decreased the Km for phosphoenolpyruvate to 0.18 mM. The apparent
activation constants for acetyl phosphate were 1.6 mM and 0.62 mM in the
presence of 0.5 and 4 mM-phosphoenolpyruvate respectively. Carbamyl
phosphate produced an increase in Vmax. and Km for phosphoenolpyruvate.
The variation of Vmax./Km with carbamyl phosphate concentration could be
described by a model in which this compound interacts with the
carboxylase at two different types of sites: an allosteric activator
site(s) and the substrate-binding site(s). Carbamyl phosphate was
hydrolysed by the action of phosphoenolpyruvate carboxylase. The
hydrolysis produced Pi and NH4+ in a 1:1 relationship. Values of Vmax.
and Km were 0.11 +/- 0.01 mumol of Pi X min-1 X mg-1 and 1.4 +/- 0.1 mM,
respectively, in the presence of 10 mM-NaHCO3. If HCO3- was not added,
these values were 0.075 +/- 0.014 mumol of Pi X min-1 X mg-1 and 0.76
+/- 0.06 mM. Vmax./Km showed no variation between pH 6.5 and 8.5. The
reaction required Mg2+; the activation constants were 0.77 and 0.31 mM
at pH 6.5 and 8.5 respectively. Presumably, carbamyl phosphate is
hydrolysed by phosphoenolpyruvate carboxylase by a reaction the
mechanism of which is related to that of the carboxylation of
phosphoenolpyruvate.