Isolated liver microsomes from rats treated in vivo with 2-aminofluorene showed an increased capacity to incorporate labeled amino acids into protein 8–48 hours after the administration of the carcinogen. This effect masked an earlier inhibitory influence of the amine. The stimulation did not appear in adrenalectomized animals, indicating that adrenal hormones might be involved.

The increase in incorporation activity of the microsomes was of the same order of magnitude whether calculated on the basis of microsomal protein or on the basis of microsomal RNA.1 The difference between preparations from normal and treated animals was diminished but still present when free RNP particles were substituted for microsomes in the incorporation system. The effect was not due to an increased active life span of the microsomes in the incubation system. Concomitantly the proportion of protein-bound isotope increased in the soluble fractions.

The incorporation activity of normal microsomes or RNP particles was increased when cell sap from treated animals was substituted for normal cell sap in the incubation system. Although both cell sap and microsomes from treated animals contributed to the increased incorporation activity, the effect of the microsomes was quantitatively more important.

*

This work was supported by research grants from the U.S. Public Health Service (C-5278), and the Swedish Cancer Society.

Preliminary reports of this work were presented at the IUB/IUBS Joint Symposium on Biological Structure and Function, Stockholm, 1960 (25), and at the Vth International Congress of Biochemistry, Moscow, 1961 (5).

1

The following abbreviations are used in the text: AAF, 2-acetylaminofluorene; AF, 2-aminofluorene; AN, 2-aminonaphthalene; ATP, adenosine triphosphate; DOC, deoxycholate; PEP, phosphoenolpyruvate; RNA, ribonucleic acid; RNP, ribonucleoprotein; TCA, trichloroacetic acid; Tris, tris(hydroxymethyl)aminomethane.

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