W. Eugene Knox

Adaptation of the rat liver tyrosine-α-ketoglutarate transaminase

Abstract Adaptive increase of the tyrosine-α-ketoglutarate transaminase occurred in the livers of rats following injections of tyrosine or of hydrocortisone. The increases were as great as 10-fold and occurred in 5 hours. Analysis showed that hydrocortisone itself was a sufficient inducing stimulus. Tyrosine was an effective inducing stimulus only if the adrenal glands or hydrocortisone also were present.

Properties and analysis of a stable derivative of pyrroline-5-car☐ylic acid for use in metabolic studies

The unstable metabolic intermediate 1Δ-pyrroline-5-car☐ylic acid (P5C or glutamic semialdehyde) cannot be isolated as a chemically pure solid because of its irreversible and concentration-dependent reaction with itself. This has been avoided by preparing it in dilute solution by periodate oxidation of dl-hydroxylysine and isolating it as a pure 2,4-dinitrophenylhydrazone from which P5C can be quantitatively regenerated. The product has been characterized by various chemical and enzymatic tests and by comparison with two other types of preparation of P5C. One of the reactions used to standardize it, reduction to proline by borohydride, also produced hydroxynorvaline in amounts indicating that an equilibrium exists between the ring and open forms of P5C and glutamic semialdehyde.

Substrate-type induction of tyrosine transaminase, illustrating a general adaptive mechanism in animals.

Summary Substrate-induced elevations of tyrosine transaminase occur, consistent with the characteristics predicted for the current model of adaptive enzyme changes in animals. This model of substrate type and hormone-type inductions is described and its general utility discussed.