Enzymatic Product release question

Tom Duncan duncant at cross.bmb.hscsyr.edu
Tue Sep 10 10:36:49 EST 1996

In article <511mpi$ika at newsgate.duke.edu>,
tschantz at galactose.mc.duke.edu (William P. Tschantz) wrote:
>I am looking for examples of any proteins that the product does not
>dissociate from the enzyme till either new substrate binds or someother
>protein accepts the product from the enzyme.

and Dima Klenchin wrote: 
> G-proteins? (Especially trimeric).
> - Hydrolyse GTP and stay with GDP until activated again to bind
> new GTP (GDP dissociation is rate limiting and is a subject for
> activation).
> - Dima

G-protein turnover is limited by slow hydrolysis and slow release of
product (GDP), which can be stimulated by other proteins, but this does
not involve stimulation of product release by binding of substrate to
another site.

The behavior of FOF1-type ATP synthases provide a good example of what
Mr. Tschantz is looking for. The enzyme has three interacting catalytic
sites. The first substrate binds very tightly and the chemical step of
ATP synthesis/hydrolysis is readily reversible, but product is also
tightly bound and dissociates very slowly. However, binding of substrate
to a second and even third site causes rapid dissociation of product
from the first site, and the next site containing substrate then becomes
the "tight" catalytic site. Of course, in the direction of ATP
synthesis, this catalytic cooperativity also depends on energy input
from a transmembrane, electrochemical gradient of protons. The first
high-resolution crystal structure for the F1-sector was published in
1994 (1st ref below). I've also included two reviews below, along with
recent articles from our lab that provide the first clear indication
that this cooperative mechanism involves the relative rotation of
catalytic sites in the complex.

Abrahams, J.P., Leslie, A.G., Lutter, R. & Walker, J.E. (1994).
"Structure at 2.8 Angstrom resolution of F1-ATPase from bovine heart
mitochondria". Nature 370, 621-628.

Boyer, P.D. (1993). "The binding change mechanism for ATP synthase -
Some probabilities and possibilities". Biochim.	Biophys. Acta 1140,

Nakamoto, R.K. (1996). "Mechanisms of Active Transport in the FOF1 ATP
Synthase". J. Membrane Biol. 151, 101-111.

Duncan, T.M., Bulygin, V.B., Zhou, Y., Hutcheon, M.L., & Cross, R.L.
(1995). "Rotation of subunits during catalysis by Escherichia coli
F1-ATPase". Proc. Natl. Acad. Sci. USA 92, 10964-10968.

Zhou, Y., Duncan, T.M., Bulygin, V.B., Hutcheon, M.L., & Cross, R.L.
(1996). "ATP hydrolysis by membrane-bound Escherichia coli FOF1 causes
rotation of the gamma subunit relative to the Beta subunits". Biochim.
Biophys. Acta 1275, 96-100.

	Thomas M. Duncan
	Dept. Biochemistry & Molecular Biology
	SUNY Health Science Center
	750 E Adams St,	Syracuse, NY 13210
	Email:	duncant at vax.cs.hscsyr.edu or
		duncant at cross.bmb.hscsyr.edu

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