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A model system is presented to explain how tyrosinase, an enzyme unique to pigmented cells such as normal and malignant melanocytes can oxidize [3H]-estradiol to radiolabeled products which closely resemble the tight binding of [3H]-estradiol to estrogen receptor. In the model system studied, tyrosinase oxidized [2,4,6,7-3H]-estradiol to [3H]-water and [3H]-estradiol metabolites, the latter of which formed ring-substituted conjugates with nucleophiles like monothioglycerol and BSA. Radiolabeled estradiol without tritium in the C-2 position (i.e. [6,7-3H]-estradiol) failed to liberate [3H]-water when exposed to tyrosinase but, nevertheless, did form ring-substituted [3H]-estradiol adducts with nucleophiles. The [3H]-water and the ring-substituted radiolabeled products possessed several characteristics of a genuine estrogen receptor protein in that they were resistant to dextran-coated charcoal (DCC) adsorption and their enzymatic formation was inhibited with non-steroidal estrogens like diethylstilbestrol. Other natural (estradiol) and synthetic (hydroxytamoxifen) estrogens which contain the phenol grouping also inhibited the enzymatic oxidation of [3H]-estradiol. Although it was difficult to differentiate estrogen receptor from tyrosinase using the conventional DCC assay system, several differences in these two proteins permitted a distinction to be made between them. First, tyrosinase oxidation of [3H]-estradiol was markedly inhibited by sulfhydryl reducing agents (monothioglycerol) that stabilize [3H]-estradiol binding to estrogen receptor. Second, estrogen receptor adsorbed by hydroxylapatite whereas tyrosinase did not, thus permitting the separation of these two proteins prior to incubation with [3H]-estradiol. We conclude that the [3H]-estradiol binding components in melanoma previously reported to be estrogen receptor probably represent instead the radiolabeled products of the tyrosinase-catalyzed oxidation of [3H]-estradiol.

The androgen-dependence of two mRNAs from rat ventral prostate coding for a 20 000 and an 11 000 dalton translation product has been investigated using complementary DNA cloned in the bacterial plasmid PBR322. One of the cloned insert DNAs from a recombinant plasmid, C-27, arrests the in vitro translation of C2 (Peeters et al. (1980) J. Biol. Chem. 255, 7017-7023). The other cloned insert DNA arrests the translation of a glycoprotein 20 000 daltons in size, with unknown function. The quantities of mRNA coding for the 20 000 and 11 000 dalton translation product were determined by hybridization of 32P-labeled inserts to filter-bound total RNA or poly(A+)-mRNA. Castration caused a decline in both mRNAs of 250-fold over 8 days. Stimulation with androgen of 5-week castrates restored the mRNA levels to 17% of intact for the 20 000 dalton translation product and 31% of intact for the 11 000 dalton translation product. The quantity of the two mRNAs found in the lateral poly(A+)-mRNA was about 1/10 that of the ventral level and the mRNAs were not detectable in the dorsal prostate, seminal vesicle or human prostate poly(A+)-mRNA populations. RNA from the ventral prostates of animals 10-21 days old contained mature levels of complementary sequences, suggesting a form of developmental posttranscriptional regulation for synthesis of the polypeptides which are not synthesized in mature quantities at this stage of development (Heyns et al. (1978) Endocrinology 103, 1090-1095; Kistler et al. (1981) Proc. Natl. Acad. Sci. (U.S.A.) 78, 737-741).

Diverging results from studies of marine oil supplementation to western diets initiated the undertaking of a double-blind crossover study, with administration to healthy volunteers for 4 weeks of either 10 g of fish oil or 10 g of vegetable oil. Each oil containing approx. 40% of n-3 and n-6 polyunsaturated fatty acids (PUFA) respectively. During the n-3 PUFA period, systolic blood pressure, plasma total lipids, triglycerides and VLDL concentrations fell significantly whereas plasma antithrombin-III (AT-III) rose. Cutaneous bleeding time increased significantly. In contrast only AT-III rose during the n-6 PUFA feeding, however, more marked than during the n-3 oil period. It is concluded that a n-3 PUFA oil supplement to the western diet exerts an effect that generally is considered as beneficial in terms of the risk of developing cardiovascular diseases. It is in this respect superior to that of n-6 PUFA, stressing the necessity of a more differentiated approach to advice on dietary PUFA enrichment than presently is exerted.