On the basis of the experiments carried out with rnhA224 mutants, we previously concluded that RNase HI is not essential for initiation of Escherichia coli chromosome replication at oriC (T. Kogoma, N.L. Subia, and K. von Meyenburg, Mol. Gen. Genet. 200:103-109, 1985). In light of the recent finding that rnhA224 is a UGA nonsense mutation which can be leaky in certain genetic backgrounds, we reexamined this conclusion with the use of rnhA339 (Null)::cat mutants. The possibility that recB+ is required for initiation at the alternative origins (oriKs) of replication in rnhA mutants was also tested. The results clearly indicated that RNase HI is not essential for oriC initiation and that recB+ is not required for initiation at oriK sites. 相似文献
We studied the resolution of racemic glycidol through esterification with butyric acid catalyzed by porcine pancreatic lipase in organic media. A screening of seven solvents (log P values between 0.49 and 3.0, P being the n-octanol-water partition coefficient of the solvent) showed that neither log P nor the logarithm of the molar solubility of water in the solvent provides good correlations between enantioselectivity and the properties of the organic media. Chloroform was one of the best solvents as regards the enantiomeric purity (e. p.) of the ester produced. In this solvent, the optimum temperature for the reaction was determined to be 35 degrees C. The enzyme exhibited maximum activity at a water content of 13 +/- 2% (w/w). The enantiomeric purity obtained was 83 +/- 2% of (S)-glycidyl butyrate and did not depend on the alcohol concentration or the enzyme water content for values of these parameters up to 200 mM and 25% (w/w), respectively. The reaction was found to follow a BiBi mechanism. (c) 1993 John Wiley & Sons, Inc. 相似文献
Head-out water immersion (HOI) induces a profound diuresis and natriuresis, which may endanger the body fluid balance of breath-hold divers during prolonged diving work. To investigate if adaptation is acquired by professional breath-hold divers, we have evaluated renal responses to 3-h HOI in 5 Korean women divers (Amas) and 11 nondiving housewives (controls). In both control and diver groups, the average urine flow during 3-h immersion was four times greater and Na+ excretion was 70%–80% greater than the pre-immersion value [urine flow: 3.7 (SD 1.0) ml·min–1 vs 0.9 (SD 0.4), P<0.001, in controls; 4.3 (SD 0.9) vs 1.1 (SD 0.4), P<0.001, in divers; Na+ excretion: 270 (SD 176) mol· min–1 vs 161 (SD 84), P<0.025, in controls; 303 (SD 31) vs 164 (SD 62), P<0.005, in divers]. In all cases, the values for a given period were not significantly different between the two groups. The plasma concentrations of Na+ and osmolality, and renal clearance of creatinine did not change significantly. However, the osmolal clearance increased [from 2.0 (SD 0.8) ml·min–1 to 2.8 (SD 0.7), P<0.05, in the controls; from 2.2 (SD 0.4) to 2.6 (SD 0.4), P<0.05, in the divers] and free water clearance changed from negative to positive values [from -1.1 (SD 0.5) ml·min–1 to 1.2 (SD 0.3), P<0.005, in the controls; from -1.2 (SD 0.4) to 1.6 (SD 1.1), P<0.01, in the divers] during immersion, again the pattern of change being similar in the two groups. It was, therefore, concluded from our study that the renal response to HOI was unchanged in the Korean women professional breath-hold divers compared to the nondiving women. 相似文献
1. 1. The purposes of this study are to find out the arrangement effects on the vapor pressure gradient across the cotton–nylon double layer and to elucidate changes in the vapor pressure gradient when an additional third layer covers the double layer.
2. 2. Model tests for single, double and triple layer system and wear test for triple layer clothing were conducted.
3. 3. It was found that up to the second layer, dryness of innermost microclimate could be maintained when cotton faced the skin (C/N).
4. 4. However, when more permeable and hydrophobic third layer (UWF) covers the double layer, the microclimate of C/N is no longer drier than N/C.
5. 5. When nylon is exposed to the skin, a larger drop in vapor pressure across the first two layers occurred for both model and wear test.
6. 6. The innermost microclimate was not necessarily kept dry when the outermost layer dissipated more moisture due to the inefficient distribution of moisture.