>During alcoholic fermentation, yeast metabolises glucose to form ethanol
>and carbon dioxide using a metabolic pathway consisting of a number of
>enzymes. By making the assumption that the yeast cell is a single
>catalytic reactant, glucose (as a control), mannose, galactose and
>fructose will be added separately to yeast solution.
Good start.
>Because the multi-based pathway consists of steps, the rate of reaction
>will be heavily reliant on the slowest rate determining step.
^^^^^^^^^^^^^^^^^^^^^^^^
Actually, the way you state this isn't too far off base, but reflects the
archaic notion. All steps are rate determing to some extent or another.
The degree of control is quantified by something called a flux-control
coefficient, which typical varies between 0 and 1. 0 would be absolutely
no control and 1 would be complete control. For an step in the pathway,
the coefficient will be greater than 0 and probably less than 1.
I've recently compiled a list of web resources on the subject (some updates
needed at: http://pw2.netcom.com/~drpauls/maths-f (hit the menu item for
metabolic control analyses.)
>Comparison
>of reaction rates of each sugar with yeast will give an indication as to
>whether different pathways, (for example not that of glucose) were
>utilised.
>>To measure the rate of reaction, substrate concentration of each
>monosaccharide will be varied and a measurement of carbon dioxide, the
>by-product of fermentation, will be obtained.
You can actually measure the rates of substrate utilization and the rate
of ethanol production. You should probably do these in addition to the
CO2. Ethanol is easy on a GC (samples can be stored for later analysis.)
Getting rates of substrate utilization requires measurements at multiple
time points. An example where this has been done (by me) is:
Schlosser, Riedy, and Bailey, 1994, Ethanol production in baker's yeast:
application of experimental perturbation techniques for model development
and resultant changes in flux control analysis, Biotechnology Progress,
10:141-154.
Regards,
Paul Schlosser
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Paul M. Schlosser, Ph.D.
Chemical Industry Institute of Toxicology (CIIT)
P.O. Box 12137
6 Davis Drive (not needed for regular mail)
Research Triangle Park, NC 27709
Voice:(919) 558-1243; FAX:(919) 558-1300; schlosser at ciit.org
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