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J. Biol. Chem., Vol. 279, Issue 1, 1, January 2, 2004
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Classics
Transamination with Purified Enzyme Preparations (Transaminase) (Cohen, P. P. (1940) J. Biol. Chem. 136, 565-584)
Philip Pacy Cohen (1908-1993), universally known as P. P. Cohen, was born in Derry, New Hampshire, attended high school in Boston, and graduated from Tufts College, now Tufts University, in 1930. He then enrolled in graduate school at the University of Wisconsin from which he received a Ph.D. degree in physiological chemistry in 1937 and an M.D. degree in 1938. Cohen was awarded a postdoctoral fellowship to work with Hans Krebs in Sheffield, England, and it was in Krebs' laboratory that Cohen's focus on nitrogen metabolism and transaminases started. Cohen completed his fellowship in the laboratory of Cyril N. H. Long at the Yale University School of Medicine with the work reported in this JBC Classic. After completion of his postdoctoral studies, Cohen returned to the University of Wisconsin as Research Associate in Physiological Chemistry and rose through the academic ranks to become Professor in 1947. In 1968, he succeeded Harold C. Bradley as Chairman of the Department of Physiological Chemistry, a post he held for 27 years. He was highly respected at the University and was asked to serve as Acting Dean of the Medical School during a turbulent 2-year period (1).1
The paper selected as a JBC Classic is impressive for its thoroughness and
insight. In addition, it places transamination reactions and transaminases on
a solid biochemical basis. Studies of transamination reactions were first
reported by Braunstein and Kritzman
(2), but as Cohen pointed out,
they had considered the reaction to be a general one involving numerous
-amino acids and -keto acids. Cohen reported in this JBC Classic
that the extract preparations, of pigeon breast muscle and pig heart used in
the study, were only highly active with three specific amino acids, alanine,
glutamic acid, and aspartic acid, in the following reactions.
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We now know, of course, that these are the major transamination reactions
responsible for amino acid synthesis from Krebs cycle intermediates. It is
notable that the -keto acid substrates for these reactions, oxaloacetic
acid and -ketoglutaric acid, had to be synthesized whereas most of the
amino acids tested were available commercially. Cohen acknowledged receiving
glutamic acid from Joseph Fruton, alanine from Vincent Du Vigneaud,
phosphoserine from Fritz Lipmann, and cysteine from Abraham White, all of whom
became distinguished biochemists.
Cohen's interests extended to other aspects of nitrogen metabolism, and he is well known, in addition, for his studies of urea metabolism. In a particularly interesting set of studies, he investigated the developmental biochemistry of metamorphosis from the tadpole that excretes ammonia to the frog that excretes urea. Cohen and his collaborators demonstrated that the rate-limiting enzymes in urea synthesis, carbamyl phosphate synthetase and argininosuccinate synthetase, increased in the liver as metamorphosis progressed and urea excretion began (3).
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FOOTNOTES
1 The biographical information for this JBC Classic introduction was entirely
from Ref. 1. 
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