Search

The iron(III) mineral cores of bacterioferritins (BFRs), as isolated, contain a significant component of phosphate, with an iron-to-phosphate ratio approaching 1:1 in some cases. In order to better understand the in vivo core-formation process, the effect of phosphate on in vitro core formation in Escherichia coli BFR was investigated. Iron cores reconstituted in the presence of phosphate were found to have iron-to-phosphate ratios similar to those of native cores, and possessed electron paramagnetic resonance properties characteristic of the phosphate-rich core. Phosphate did not affect the stoichiometry of the initial iron(II) oxidation reaction that takes place at the intrasubunit dinuclear iron-binding sites (phase 2 of core formation), but did increase the rate of oxidation. Phosphate had a more significant effect on subsequent core formation (the phase 3 reaction), increasing the rate up to five-fold at pH 6.5 and 25 °C. The dependence of the phase 3 rate on phosphate was complex, being greatest at low phosphate and gradually decreasing until the point of saturation at ~2 mM phosphate (for iron(II) concentrations <200 µM). Phosphate caused a significant decrease in the absorption properties of both phase 2 and phase 3 products, and the phosphate dependence of the latter mirrored the observed rate dependence, suggesting that distinct iron(III)-phosphate species are formed at different phosphate concentrations. The effect of phosphate on absorption properties enabled the observation of previously undetected events in the phase 2 to phase 3 transition period. [ABSTRACT FROM AUTHOR]

The article discusses causes of human fertility. Comparative research focusing on the general attributes of whole societies has so far proved particularly useful for increasing our understanding of changes in the timing of childbearing and for suggesting possible directions for additional research. Research focusing on the attributes of individuals has become increasingly common with the development of survey research techniques, the extension of census-taking and the elaboration of cross-tabulations of census and vital registration data made possible by the advent of computerization. The article focuses on the relation between fertility and various carefully controlled social and psychological variables. It is useful for the acquisition of information required in demographic forecasting and the establishment of goals and procedures associated with social planning. The article thus develops a healthy scepticism about so-called "social indicators", if not about the whole "social indicators" movement, itself.

This paper outlines a framework for studying the social-cultural determinants of family size in 20 low mortality countries of controlled natality. Two broad hypotheses are proposed: (1) Family size varies inversely with the availability of alternatives for the satisfaction of interests presumably satisfied by having children. (2) Family size is smallest under two polar sets of conditions: (a) where the social setting maximizes the individual's expectation that his interests and those of his children will be satisfied, and (b) where the social setting minimizes this expectation. Representative social indicators for making the necessary international comparisons are enumerated, and the steps in their construction discussed. [ABSTRACT FROM AUTHOR]