Usefulness of the dietary phytic acid/ zinc molar ratio as an index of zinc bioavailability to rats and humans

Evidence suggests that rats can tolerate a dietary phytate/Zn molar ratio greater than 15 if the dietary Zn concentration is high. High dietary Ca exacerbates the effect of phytic acid on Zn utilization by rats. In a short term (15 d) balance trial with adult men, we observed slightly greater Zn balance when whole compared to dephytinized wheat bran was consumed (molar ratios 12 and 1.2, respectively). There was, however, greater fecal excretion of Zn during the first 5 d whole bran was consumed. In a second study, Na phytate was the major source of phytic acid and Zn balance was less when the phytate/Zn molar ratio was greater than 16 compared to 4. The difference was not significant, however, and there was evidence of physiological adjustments to maintain homeostasis when the high ratio diet was consumed. Mean Zn intake averaged 17 mg (0.26 mmole) and 11 mg (0.17 mmole) daily for the bran and Na phytate studies, respectively. The level of Zn intake may influence the response of humans to varying phytate/Zn ratios. Comparison of isotope retention studies and the balance data is discussed. Some information on the relationship of dietary Ca to the phytate/Zn effect in human diets is gathered from current literature. The phytate/Zn molar ratio is a useful index of Zn bioavailability.     

Sulphate activation in higher plants

Summary ATP-sulphurylase was detected in extracts of roots and leaves of several species of higher plant. The enzyme occurs in the supernatant fraction, has a pH optimum of 8.0 and an absolute requirement for Mg²⁺ ions. Sulphurylase activity is inhibited by selenate and molybdate but not by cysteine, methionine, glutathione, or thiol reagents. The synthesis of sulphurylase by turnip, lettuce, tomato, and Lemna plants grown under aseptic conditions is neither induced by sulphate nor repressed by cystine, and in the latter respect sulphate activation in plants differs from than in micro-organisms. APS-kinase could not be detected in extracts of any tissue although its product was stable under the conditions used. Sulphate reduction in higher plants may thus proceed via adenylysulphate and not via phosphoadenylylsulphate as in many micro-organisms.     

Anti-masculinizing action of estradiol and cyproterone acetate: Regulation of a protein fraction with phospholipase-A2 stimulatory and masculinizing activities

Recently we have identified a protein fraction (55–63 K) from male and testosterone-exposed female mouse genital tract, which stimulates phospholipase A₂ (PLA₂) and induces masculine differentiation in an undifferentiated mouse genital explant, suggesting a role of this protein in the action of testosterone. In the current study we have further investigated the role of this protein by determining whether anti-masculinizing agents, namely, estradiol and cyproterone acetate, have any effect on the production of this protein. The results described here indicate that a protein fraction containing PLA₂ stimulatory activity was present in both control male and estradiol- or cyproterone acetate-exposed male fetal genital tract. However the specific activity of the PLA₂-stimulatory protein was significantly higher in the control males than in the experimental males. We did not find any major difference in the behavior of this protein fraction in various chromatographic steps except that in CM-sepharose column; the PLA₂-stimulatory activity from the male preparation was eluted in two overlapping peaks with 0.3 and 0.25 M NaCl and that from the treated males was eluted only with 0.25 M NaCl. The SDS-gel analysis of this protein fraction revealed a doublet band (55 and 63 K) in control samples and primarily a 63 K band in experimental samples. The protein fraction from all these sources showed a significant difference in their biological activity. The control male preparation induced Wolffian duct whereas the estradiol sample was completely ineffective and the cyproterone acetate sample was partially effective in inducing Wolffian duct. Thus, it appears that the protein fraction has a role in the masculinizing action of testosterone.