July 8, 1958

Dr. Efraim Racker &

Public Health Research Institute
Foot E, 15h Street &

New York 9, New York

Dear Efraim:

I noticed in this week's Science the adoption of a standard unit for
enzyme activity by your sub-committee, This seems to me an urgent neces=
sity long overdue,

I would only make the following small comments# one, that you try
to contrive an easy name for this unit which will be immediately unders
stood as referring to your standards, a name which should be readily
abbreviated. Iwo, it should not be difficult to cope with polymerie
subetrates by specifying that in these cases the unit should be based
on the number of active groupe which are split or converted, In fact,
I would believe that this would be a sounder basis than the number of
moles of substrate utilized in any instance where a substrate molecule
has more than one reactive site, for exampl@ oxidizable phenolss, Where
you have successive oxidation of the a:me mélecule by the same enzyme or
by an unresolved enzyme complex I should think that a definition based
on the whole molecule might be confusing, If you confine your attention
to the number of unit operations catalyzed by the enzyme this difficulty
should disappear, In any case, I would suppose tiat an author would have
to specify what he is using as his tern of reference if there is any
possible ambiguity. ‘hese ambiguities are most likely to arise in dise
cussing the unitage of ensyme complexes rather than purified preparations, —
but 1 think the notation would be increased if the convention ineluded both
cases, Conf te

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Yours sincerely,

Joshua Lederberg
Professor of Medical Geretics

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