On Mon, 21 Aug 2000, Petr Kuzmic wrote:
>> "Michael C. Kohn" wrote:
> > [...]
> > Some of the enzymes (e.g. fatty acyl CoA
> > synthetase) lost activity when they were purified from the membranes
> > in which they were embedded. But these problems are not
> > insurmountable, and such effects were represented in the model.
>> Michael, do you have literature references where one could look to see
> how the kinetics membrane-bound enzymes in vivo could be handled? [...]
> -- Petr
Petr, the alternative, more rigorous approach to membrane-bound enzyme
kinetics originate basically from the Chemical Engineering field; it
differentiates between intrinsic (microscopic, as in solution) and
inherent (solely resulting from their physical state) properties of
immobilized enzymes. The combination of both yields the effective
properties of the catalytic system (macroscopic, as observed out of the
black box).
The latter, most often dealt-with by most biologists, yield a distorted
picture of the system's behavior, especially when the interpretation of
the results is based on a (tacite) assumption that "ideal" conditions
prevail...
If you're interested please refer to this central (relatively recent)
review:
*Engasser, J.-M. and C. Horvath (1976). Appl. Biochem. Bioeng. 1:127-220.
A fascinating discussion, pertaining to the effective consequences of
enzyme organization can also be found at:
*Ricard, J., N. Kellershohn, et al. (1989). Spatial order as a source of
kinetic cooperativity in organized bound enzyme systems. Biophys J
56:477-487.
The modelling of these aspects is tough and refractive to automation due
to the non-linearity of the underlying phenomenological differential
equations. I'd love to see packages like 'gepasi', 'biokin', 'jarnac'
etc. (sorry I can't enumerate all...), implementing that.
Some of my (and many cited others') work using localized probes deals with
the "diagnosis", demonstration and discussion of heterogeneous effects in
cellular catalysis:
*Aflalo, C. and N. Shavit (1984). A new approach to the mechanism of
photophosphorylation: modulation of ATP synthetase activity by limited
diffusibility of nucleotides near the enzyme. Curr. Top. Cell. Regul. 24:
435-445.
*Aflalo, C. and M. DeLuca (1987). Continuous monitoring of ATP in the
microenvironment of immobilized enzymes by firefly luciferase.
Biochemistry 26:3913-3919.
*Aflalo, C. (1991). Biologically localized firefly luciferase: a tool to
study cellular processes. Int. Rev. Cytol. 130:269-323.
*Aflalo, C. and L. A. Segel (1992). Local probes and heterogeneous
catalysis: a case study of a mitochondria-luciferase-hexokinase coupled
system. J. Theor. Biol. 158:67-108.
*Aflalo, C. (1997). Localized firefly luciferase probes ATP at the surface
of mitochondria. J. Bioenerg. Biomembr. 29:549-559.
---------------------------------------------
Sincerely,
Claude
PS: Best regards from Itzhak Fishov
Claude Aflalo ########################## Phones: Office 972-7-6472118 ####
Unit for Science Teaching/Dept. of Life Sciences Lab 972-7-6472119
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P.O.Box 653 email: aflaloc at bgumail.bgu.ac.il
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