Paul R. Libby

Steroid Sulfatase Activities in Human Breast Tumors

Summary The ability of human breast tumor preparations to hydrolyze DHEA, estrone, and testosterone sulfates was studied. Of the 85 tumor preparations examined, 31 tumors contained an estrogen sulfatase activity and 19 of which also exhibited sulfatase activity toward DHEA; but there was no testosterone sulfatase in any of the 31 tumor preparations. The remaining 54 tumor preparations showed no sulfatase activity toward any of the three steroid sulfates examined. The present data also disclose that the levels of sulfatase activities do not affect those of sulfotransferase activities in the tumor preparations. Further, the ratio of sulfotransferase activity with DHEA and estradiol as substrates is not related to the sulfatase activity in these tumor preparations.

Rat liver nuclear N-acetyltransferases: Separation of two enzymes with both histone and spermidine acetyltransferase activity☆

Abstract Two similar histone acetyltransferases have been separated from rat liver nuclei and purified 500-fold. Both enzymes also acetylate spermidine and spermine but diamines are not acetylated. Both enzymes preferentially acetylate histone 3; among the remaining histones H2A and H2B are good substrates, whereas H1 and histone 4 are poor substrates. Apparent Michaelis constants for spermidine were about 2 × 10−4 m ; apparent Michaelis constants for acetyl coenzyme A were 1.5 × 10−5 and 10−5 m for enzymes A and B, respectively. At low concentrations DNA inhibits histone acetylation by enzyme A (50% inhibition at 25 μg/ml DNA). Enzyme B is relatively insensitive to DNA. This suggests the possibility of separate intranuclear localization of the two enzymes.

Histone acetylation by cell-free preparations from rat uterus: In vitro stimulation by estradiol-17β

Abstract Histone acetylation has been shown to be a normal component of the metabolism of these nuclear proteins. Pogo, Allfrey, and Mirsky (1966) showed that human lymphocytes acetylated their nuclear histones during culture, and that the acetylation was increased during exposure to phytohemagglutinin (PHA). Allfrey et al. (1966) have also described the stimulation of histone acetylation in liver by cortisol. Nohara et al. (1966) have demonstrated that partially purified preparations from liver have the ability to acetylate histones. It was of interest to examine the capacity of the uterus of the immature rat to acetylate histones. The results described in this paper demonstrate the presence in the uterus of the immature rat of an enzyme system that acetylates histones. In addition, in vitro stimulation of the cell-free system by the female sex hormone, estradiol-17β, is described.

Rat Mammary Gland RNA: Incorporation of C14-Formate and Effect of Hormones and 7,12-Dimethylbenz[alanthracene

In female rats, the incorporation of sodium C14-formate into mammary gland RNA decreases immediately after a singlefeeding of 20 milligrams of 7,12-dimethylbenz[a] anthracene. In males, there is a gradual increase in the incorporation. In castrated rats, the decrease or increase of C14-formate incorporation is dependent on the presence of estrogen or androgen, respectively.

Multiple forms of histone acetyltransferases in the cytosol of calf endometrium

The histone acetyltransferase (EC 2.3.1.-) activity of calf endometrium cytosol has been separated into three separate activities by stepwise chromatography on DEAE-cellulose. In addition to differential elution from the DEAE-cellulose, the three activities are differentiated by their pH optima, preferences for histone subfractions as substrates, and stability to heat denaturation. Peak I has an optimum of pH 8.7 and preferentially acetylates histones F2b and F3; Peak II has an optimum of pH 8.5, and preferentially acetylates histone F2al followed by histone F2b; Peak III has an optimum of pH 9.5, and had similar specificity to Peak II. Peak III is appreciably more stable at 60 degrees C than is Peak II. None of the peaks transferred acetate to other proteins tested or to tRNA. These studies suggest the presence of multiple histone acetyltransferases in tissue cytosols.

Lack of Sulfate-Activating Enzymes in Human Breast Tumors

Summary Preparations from human breast tumors which are inactive in the formation of steroid sulfates are shown to be lacking the two sulfate-activating enzymes, sulfate adenylyltransferase, and adenylylsulfate kinase, and to have measurable amounts of 3-β-hydroxysteroid sulfotransferase and estrone sulfotransferase. The study also suggests that the sulfate-activating enzymes are the limiting factor in determining the level of steroid conjugating activity of the tumor preparations that have the ability to form steroid sulfates.