We have proposed negative cooperativity for
human liver L-type pyruvate kinase, a phenomenon
also observed in: Lineweaver-Burk plots V⁻¹
versus [phosphoenolpyruvatel]⁻¹ were straight lines
at low phosphoenolpyruvate concentrations, and
bent downward near they axis (high phosphoenolpyruvate
concentrations). Our conclusions were
drawn from experiments performed at Mg²⁺total =
12 mM or 20 mM. However, phosphoenolpyruvate
has been proposed to bind Mg²⁺free with a Keq =
5.5 X 1O⁻³ M⁻¹ at 25°C. So, at high phosphoenolpyruvate
concentrations Mg²⁺free would be removed
from the reaction mixture. We investigated the
hypothesis that the phenomenon interpreted as negative
cooperativity is in fact due to removing
inhibitory Mg²⁺free from the reaction mixture at high
phosphoenolpyruvate concentrations. Our results are
in favour of this hypothesis
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