Frozen spin targets in ribosomal structure research.

Polarized neutron scattering strongly depends on nuclear spin polarisation, particularly on proton spin polarisation. A single proton in a deuterated environment then is as efficient as 10 electrons in X-ray anomalous diffraction. Neutron scattering from the nuclear spin label is controlled by the polarisation of neutron spins and nuclear spins. Pure deuteron spin labels and proton spin labels are created by NMR saturation. We report on results obtained from the large subunit of E. coli ribosomes which have been obtained at the research reactor of GKSS using the polarized target facility developed by CERN. The nuclear spins were oriented with respect to an external field by dynamic nuclear polarisation. Proton spin polarisations of more than 80% were obtained in ribosomes at temperatures below 0.5 K. At T = 130 mK the relaxation time of the polarized target is one month (frozen spin target). Polarized small-angle neutron scattering of the in situ structure of rRNA and the total ribosomal protein (TP) has been determined from the frozen spin targets of the large ribosomal subunit, which has been deuterated in the TP and rRNA respectively. The results agree with those from neutron scattering in H2O/D2O mixtures obtained at room temperature. This is a necessary prerequisite for the planned determination of the in situ structure of individual ribosomal proteins and especially of that of ribosome bound mRNA and tRNAs.     

Management of hyperandrogenism in adolescent girls.

Hyperandrogenism in adolescent girls can be a troubling problem because of the difficulty in establishing a diagnosis and in prescribing appropriate therapy. Androgen excess in adolescent patients encompasses a spectrum of clinical presentations, including acne, hirsutism, oligomenorrhea, amenorrhea, virilism, and ovarian cysts. Androgen excess is a clinical and chemical feature of idiopathic hirsutism, late-onset forms of congenital adrenal hyperplasia, and polycystic ovarian disease; in some cases, functional hyperandrogenism is discussed. We recommend screening for hyperandrogenism by measuring blood levels of testosterone, dehydroepiandrosterone sulfate, and delta 4-androstenedione, while others propose a first dexamethasone suppression test for evaluation of free testosterone, dehydroepiandrosterone sulfate, and cortisol. Treatment will be chosen according to particular symptoms such as acne, hirsutism, obesity, or oligomenorrhea.     

EFFECT OF CONTROLLED TEMPERATURES ON GAMETOGENESIS IN THE GASTROPODS PHYSA ACUTA (PHYSIDAE) AND BULINUS TROPICUS (PLANORBIDAE)

The effects of a range of constant temperatures on gametogenesiswere investigated in two freshwater snail species which occursympatrically in the Umsin-dusi River, Natal, South Africa,Physa acuta (invasive) and Bulinus tropicus (endemic). Bothwere shown to be simultaneous hermaphrodites with slight protandry.An increase in temperature accelerated the process of gametogenesisbut P. acuta responded more rapidly to these changes than B.tropicus. This, coupled with the greater fecundity and shorterincubation period of P. acuta, gives it a reproductive advantageover the endemic species, providing a possible explanation forthe invasive's success in rapidly repopulating disturbed riverinehabitats. (Received 16 November 1990; accepted 1 May 1991)     

The interaction of temperature and fish size on growth of juvenile turbot

Growth rate of tagged juvenile turbot was significantly influenced by the interaction of temperature and fish size. The results suggest the optimum temperature for growth of juvenile turbot in the size range 25–75 g is between 16 and 19°C. Optimal temperature for growth decreased rapidly with increasing size, and is between 13 and 16°C for 100 g turbot. Although individual growth rates varied highly at all times within the temperature treatments, significant size rank correlations were maintained during the experimental period. The study confirms that turbot exhibit ontogenetic variation in temperature optimum, which might partly explain different spatial distribution of juvenile and adult turbot in ocean waters.     

Lability of fat stores in peripubertal wild house mice

Summary Traditionally, the adaptive value of mammalian white fat stores is considered in relation to longterm needs such as providing protection against the vagaries of winter or signalling the reproductive system when energy reserves are sufficient to risk pregnancy. As shown here, the fat stores of young house mice could not serve such needs. Despite prolonged acclimation and excess nesting material, food deprivation at 10°C significantly lowered the fat stores of peripubertal female house mice in only 12 h, and would exhaust them in 30 h. Even close to thermoneutrality (24°C) the calculated time to exhaustion was only 70 h. The fat stores of a young house mouse are obviously too meager to offer any meaningful protection over a winter of several months duration, or even over a 5–6-week cycle of pregnancy and lactation. Furthermore, in a wild habitat where food availability and ambient temperature can vary rapidly and greatly, such fat stores would be too labile to effectively coordinate puberty with somatic development.     

Female reproductive biology of the sand smelt in brackish lagoons of southern France

The breeding season of Atherina boyeri living in the brackish lagoons of Mauguio, Pérols and Méjean (Hérault, southern France) was very protracted (February-September). The peak of the reproductive effort occurred in April, May and June. Larger fishes started spawning earlier, and stopped later, than smaller ones. Batch fecundity varied from 4 to 447 oocytes and was positively related to female length and weight. Monthly mean fecundity increased at the beginning of the breeding season and decreased between June and July. Individual mean oocyte diameter ranged from 1.34 to 1.94 mm and was not related to fish length. Monthly mean oocyte size declined throughout the breeding season as water temperature rose. There was no trade-off between number and egg size. The strategy of these sand smelts seemed well adapted to ensure spawning success without endangering their survival. The highest reproductive effort period occurred in such a way that environmental conditions were suitable to the best survival and growth of hatched larvae. When breeding ceased, fishes, particularly the youngest ones, had enough time to improve their condition before overwintering.     

Improved Kinetic Resolution by Enzyme-Catalyzed Parallel Reactions

Competitive parallel reactions with opposite enantioselectivity are presented as a strategy to enhance the enantiomeric product purity in enzymatic kinetic resolution. Lipase-catalyzed simultaneous hydrolysis and amidation of racemic methy 12-chloropropionate led to significantly improved amide yield and enantiomeric excess. Process results can be controlled by changing the hydrolysis/amidation reaction rates through variation of the solvent and the initial amine concentration. This is described by a kinetic model.