Linkage analysis of the murine mos proto-oncogene on chromosome 4

A linkage analysis of the murine Mos gene, which codes for the c-mos proto-oncogene, was performed in 88 backcross progeny of an interspecies cross of laboratory mice and Mus spretus. Linkage was tested for four different genes on mouse chromosome 4: Aco-1, Mup-1, b, and Ifb. The gene order (from centromere) with intervening percentage recombination is Mos-15.9 (+/- 3.9)-Aco-1-5.6 (+/- 2.4)-Mup-1-3.4 (+/- 1.9)-b-5.6 (+/- 2.4)-Ifb. These results confirm the previous assignment of Mos to chromosome 4 on the basis of segregation in somatic cell hybrids (D. Swan et al., 1982, J. Virol. 44: 752-754) and show furthermore that Mos and the Ifa/Ifb clusters are not tightly linked as a group of intronless genes, but are separated by a map distance of 30.6 +/- 4.9 recombination units. The linkage data obtained in the present study place Mos in a region compatible with the physical map (D. W. Threadgill and J. E. Womack, 1988, Genomics 3: 82-86).     

Effect of acute altitude hypoxia on fatty acid proportion in the plasma of rats of different ages

Using gas chromatography, the authors studied the development of the proportion of 25 saturated and non-saturated fatty acids in the plasma of Wistar rats of their own breed aged 5, 10, 14 and 25 days and adult (both sexes), and in three age groups (5 and 14 day and adult) they determined the effect of acute altitude hypoxia. Fatty acids were determined as methylesters (FAME) (Base 1978), using the method already described by Smídová et al. (1984a), in mixed blood plasma obtained from decapitated control and experimental animals. Altitude hypoxia, which corresponded to 9 000 m, lasted 20 min. The temperature was kept stable at 25 degrees C. Marked changes occurred during ontogenesis in the proportion of total fatty acids (TFA) in the plasma; the proportion of sigma non-saturated FA fell significantly during maturation, chiefly in favour of monoene FA, with a resultant significant drop in their reciprocal index (sigma saturated/sigma monoene). The proportion of all saturated FA amounted in 5-day-old rats to 54% of the total quantity, but in adult rats to only 40%. Acute hypoxia had a demonstrable effect in all three age categories. In 5-day-old rats it led to significant changes in 7 FA and in adult rats in 10. In both 5-day-old and adult animals it produced an increase in the arachidonic acid level. The results are discussed in relation to previous findings on the effect of the same hypoxia on FA proportion in various parts of the CNS of rats of different ages.     

Reactivity of consecutive basic amino acid residues in peptides

Different tetrapeptides of general formula L-Ala-X-X-Gly, possessing a basic doublet in the second and third position (X = Arg or Lys), have been synthesized as free or N-acetylated molecules. The chemical reactivity of the arginine guanidino group and of the lysine epsilon-amino group were studied using respectively the Sakaguchi and the ortho-diacetylbenzene reactions, in the tetrapeptides as well as in related molecules. In both cases, the colour yield is markedly influenced by the length of the polypeptide chain and by the relative positions of the arginine and lysine residues, suggesting the occurrence of intramolecular bonds within the tetrapeptide molecule. Tryptic hydrolysis of the tetrapeptides was followed by evaluating the amino acids or peptides which appear to be specific for the different possible cleavages at the arginyl or at the lysyl bonds. The susceptibility to trypsin of the carboxylic group of the second basic amino acid decreases progressively in the order Lys-Arg greater than Arg-Arg much greater than Lys-Lys greater than Arg-Lys, which shows a fair correlation with the intra-cellular cleavage of the bonds observed during the processing of preproteins of of the precursors of several physiologically active peptides.     

Role of Asp-9 and Glu-36 in the active site of the pneumococcal CPL1 lysozyme: an evolutionary perspective of lysozyme mechanism.

The role of carboxylic amino acids Asp-9 and Glu-36 in the activity of CPL1 lysozyme was investigated by site-directed mutagenesis. The enzymatic activity of the single mutants D9E, D9N, D9H, D9K, D9A, E36D, E36Q, E36K, and E36A and of the double mutant D9A-E36A was analyzed using a highly sensitive radioactive assay. All mutants but D6K showed detectable activities. Interestingly, the mutants E36D and E36Q retained 67% and 37% activity, respectively. Amino acid replacements at position 9 turned out to be more critical for activity than at position 36. In analogy to the mechanism described for hen egg-white lysozyme, where the proton donor play a central role, we propose that, in the CPL1 lysozyme, Asp-9 might act as the proton donor for activation of the substrate, and Glu-36 could help in the stabilization of the intermediate oxocarbocation. The residual activity of lysozyme mutants lacking one or two of the acidic amino acids may be explained by the participation of a water molecule as proton donor and/or to electrostatic contributions in the active center stabilizing the transition state of the reaction. Our results are in agreement with the hypothesis that enzymes have been optimized during evolution from an ancestral protein able to bind more tightly the transition state of the substrate than the substrate itself, by the acquisition of amino acids serving a function in catalysis.     

Effects of changes in circulating volume and in arterial pressure on plasma renin activity in the intact rat

The effects of changes in arterial pressure and in circulating volume on Plasma Renin Activity (PRA) in the intact rat were compared by two experimental procedures. Gradual volume depletion was induced by intraperitoneal injection of a hyperoncotic polyethyleneglycol solution (PEG) in absence of acute changes in Systolic Arterial Pressure (SAP). SAP was measured in the conscious state by the tail cuff technique. Plasma Protein Concentration (PPC) and Hematocrit (Hct) increases after PEG injection were compared as the index for measuring the Plasma Volume Reduction (PVR). PRA showed a significant (p less than 0.001) linear relationship with PPC, suggesting a direct dependence of renin secretion on volume depletion. Acute changes in the circulating volume were induced by controlled hemorrhages of 5.0, 10.0, 15.0 and 20.0 ml of blood/kg body weight. The increase in PRA showed a significant relationship with the changes in circulating volume, but it did not show any dependence on the changes in Mean Arterial Pressure (MAP). Our results suggest that, in the intact and conscious rat, renin secretion responds to the information from the cardiopulmonary volume receptors rather than to that from the high pressure receptors.