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enzyme definition - help

Douglas C Pearson dopearso at magnus.acs.ohio-state.edu
Fri Feb 9 12:50:23 EST 1996

Harald Teicher <hteicher at biobase.dk> wrote:
>Could somebody please enlighten me on the following problem:


>Question: When fnr, plastocyanin and ferredoxin are involved in catalysing
>the process of oxidoreduction, and are not consumed in the process, why is
>only fnr classified as an enzyme....?

>My guess: plastocyanin and ferredoxin are electron transfer proteins, while
>fnr is also involved in the transfer of H+. On the other hand, the definition
>of an enzyme no longer seems to include the word _protein_ (ie. ribozymes) so
>plastoquinone, which is a hydrogen/electron carrier might also fall under the
>category enzyme.(?) Taking things to extremes, might the entire photosynthetic
>electron transport apparatus not be defined as an H2O:NADP+ oxidoreductase..;-

your guess is reasonable, but my inkling is that the reasons are more historic
or semantic than anything else.  i personally have a very tight means of
defining what an enzyme is [to wit, a protein that catalyzes a specific
condensation, hydrolysis, or other major chemical change in a molecule; proton
or electron transfer reactions do not fall in the "major chemical change"
category] and everything else falls into an outlier category, such as "electron
transport proteins" [which i use to refer to my beloved plastocyanin and
cytochrome f].  other people have different definitions of "enzyme."  the truly
important question is not what we call the thing, rather what does the thing

of course, i'm a physicist.  your mileage on these opinions may vary.

chuck pearson - dopearso at magnus.acs.ohio-state.edu
osu biophysics program, daddy of amelia catherine pearson.

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