KINETICS ON THE MICROBIAL SCALE
by H. A. Deans
To chemical engineers the term kinetics implies the attempt to interpret
rates of chemical reactions, quite often on the basis of reasonably com-
prehensive data on the system of interest. The number of reactions
involved is usually small, and the worst that can happen is a mass-transfer
limitation to obscure the rate mechanism or something of equivalent
complexity.
When we first look at the reaction systems which take place in living
organisms, we are immediately assaulted by appalling qualitative dif-
ferences. The number of reactions is large; intermediates are shared by
several different reactions; hardly any reaction goes without the very
efficient catalysis of an enzyme; and the molecules involved are mostly
very large and apparently unnecessarily complicated. My first impulse
was to ignore this internal complexity, and to try to apply pseudo-kinetics
to the “overall” process of respiration and substrate consumption.
A little bit of reading in the biochemistry literature was sufficient to
convince me that this course would lead nowhere. It soon became
evident that the interaction of the many reactions occurring in a living
cell is of primary qualitative importance, and that any attempt to ignore
the details of the mechanisms would miss the point altogether. We are
seeking an understanding of how living cells utilize substrates and
oxygen, control their own growth, react to changes in environment,
and do all the other things that only living cells can do; our only avenue
of attack is through the detailed mechanisms of the biochemical reactions
which accomplish all these things.
The present state of mechanistic knowledge is such that we can begin
the job of formulating the kinetics problem, if nothing else, ɪ will try to
write out the algebra for an important set of reactions and show that the
mathematical formulation has some of the properties of the living system.
The algebraic description can then be a basis for analyzing sensitivity
and control of the system, which is a potentially rich source of inverse
information.
Editor’s Note: Mr. Deans is Associate Professor of Chemical Engineering at
Rice University.
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