A study, using ab initio quantum chemical methods, of the first step in the reaction mechanism of Rubisco, the enolization of the substrate, ribulose bisphosphate, is reported. This is the first such study that takes into account the likely roles of critical features within the active site. On the basis of molecular dynamics relaxation of the complex between activated enzyme and substrate using X-ray crystallographic structures as starting coordinates, a 29-atom fragment that mimicked the active site was constructed. States along a proposed reaction pathway were calculated using density functional theory and Moller-Plesset second-order perturbation theory. The results are consistent with the postulate that the base that abstracts the C3 proton of ribulose bisphosphate is the metal-stabilized carbamate of Lys-201 formed during the activation process. The calculations suggest that the active-site residue, Lys-175, is charged before enolization commences and they indicate a possible means by which the enzyme directs the incoming CO2 to attack the C2 carbon atom of the enediol, rather than the chemically very similar C3 atom.
Three experiments have been conducted with the aim of producing calves from frozen, sexed embryos by combining embryo splitting and cytogenetic methods. In the first experiment, the efficacy of the bisection technique was assessed by transcervical transfer of 10 monozygotic pairs of half embryos to 10 synchronised heifers. Thirteen calves were produced, including four sets of identical twins. In the second experiment, one of the halves of each of eight split embryos was transferred while the other was processed for sexing by identification of the sex chromosomes. In the third experiment, one of the halves from each of 28 embryos was frozen while the other half was used for sexing. Eleven of the 16 which were sexed have been transferred with the production of three calves of the predicted sex. The overall sexing rate was 60 per cent and the calving rate following transfer of sexed embryos was 60 per cent and 23 per cent for fresh and frozen halves respectively.
Novel stimuli within several sensory modalities are potent determinants of action. Research in primates, carnivores, and rodents has indicated the importance of novel visual, auditory, and somatic stimuli for behavioral arousal and orientation (Welker, 1961). Probably for theoretical reasons, there has been a tendency to emphasize the independence of such "stimulus motivation" from need-involved behavior such as eating. The results presented below encourage a conceptual reorientation in this respect by demonstrating an influence of novelty of both edible and "inedible" materials on the eating and gnawing behavior of rats. METHOD SubjectsThe 5s were 10 Sprague-Dawley male rats, S of which were ophthalmectomized under ether at 25 days of age to eliminate visual cues. All 10 were kept in individual cages (21 cm. by 21 cm. by SO cm.) and tested when they were between 77 and 197 days of age. MaterialsThe rats were presented with a variety of nutritive and nonnutritive materials. Two brands of standard food pellet-Rockland Rat Diet (Pellet A) and Purina laboratory chow (Pellet B)-were used as the basic food. The five nonnutritive substances offered were two types of rubber eraser, nontoxic colored wax crayons, chalk sticks, and Alphacel, a powdered cellulose. Granulated sucrose sugar cubes, Ry-Krisp wafers, Rockland dog pellets, Purina monkey chow pellets, and 1-cc pieces of coagulated chicken egg albumen were offered as nutritive solids, and tap, distilled, and 0.1% saccharin water as fluids. ProcedureThe basic presentation period for all materials was 6 consecutive days and the entire experiment consisted of 20 such periods run consecutively. Standard food pellets (Pellets A or B) were offered on every test day
A. PERRONE. 1985. A direct technique for the preparation of chromosomes from early equine embryos. Can. J . Genet. Cytol. 27: 365-369. A technique is described for the preparation of banded chromosomes from early equine embryos cultured for less than 10 h in a medium containing bromodeoxyuridine. In addition to standard Giemsa staining and C-banding, chromosomes thus prepared can also be R-banded by either the RBA or the RB-FPG methods. This technique is rapid, repeatable, and limits cell loss, making it ideal for the preparation of early embryos. ROMAGNANO, A., W. A. KING, C. -L. RICHER et M .-A. PERRONE. 1985. A direct technique for the preparation of chromosomes from early equine embryos. Can. J. Genet. Cytol. 27: 365-369. Une technique a kte mise au point pour obtenir des chromosomes marques d'embryons kquins precoces; elle requiert une culture de moins de 10 h dans un milieu contenant du bromodeoxyridine. En plus de la coloration standard au Giemsa et du marquage C, les chromosomes sont ainsi prepares a reveler des bandes R par deux methodes: RBA et RB-FPG. Cette technique est rapide et fiable; de plus, comme elle permet de conserver la majorit6 des cellules, elle est idkale pour la preparation directe des embryons prdcoces.
Confusion exists as to whether the oocytes of the domestic horse are ovulated at the first meiotic metaphase (MI) or the second (MII). In this study eight oocytes were collected from the preovulatory follicles of 16 mares 36 h after human chorionic gonadotropin CG treatment. Six of the eight oocytes were judged to be at MII by the presence of the first polar body and this judgement was confirmed by semithin sectioning in one. Of the two that had no polar body, one was found to be at MII after fixation for chromosomal analysis and the meiotic stage of the other remained undetermined. Since all seven oocytes yielding conclusive evidence were at MII, it was concluded that horse oocytes, like those of most mammals studied, are ovulated after completion of the first meiotic division and formation of the first polar body.
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