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Tryptophan Pyrrolase of Liver

I. ACTIVATION AND ASSAY IN SOLUBLE EXTRACTS OF RAT LIVER

W. Eugene Knox 1, Marta M. Piras 1, and Keiko Tokuyama 1

From the 1 From the Department of Biological Chemistry, Harvard Medical School, and the Cancer Research Institute, New England Deaconess Hospital, Boston, Massachusetts 02215

Inactive forms of the tryptophan pyrrolase occur in soluble rat liver preparations. Their slow activation is responsible for the previously observed acceleration of this reaction. Maximal activation of the enzyme occurs during a 30-min preincubation with its substrate, l-tryptophan, and ascorbic acid, in the case of livers from tryptophan-treated rats, and with these additions plus methemoglobin as a source of the hematin prosthetic group, in the case of livers from untreated and hydrocortisone-treated rats. Although similar additions are necessary for the catalytic activity, the activation can occur when catalysis is prevented by anaerobiosis. Activation and catalysis are separate reactions.

The total activities in rat livers assayed after this maximal activation are higher and more reproducible than from previous measurements. Greater increases in the enzyme activity are found with this assay procedure than by previous assays, after treatment of the rats with tryptophan and especially with hydrocortisone.

Submitted on August 17, 1965


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