PubMed · 4483555
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1972. What does the analyzer really read?. https://pubmed.ncbi.nlm.nih.gov/4483555/
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The hydrolytic activity of lambda exonuclease, a highly processive enzyme, is inhibited by high pressure. When assayed at 67 MPa, the activity is 87% of the atmospheric rate; increasing the pressure to 336 MPa causes a greater than 99% inhibition of the enzyme activity. Decreasing the pressure from 336 MPa to 67 MPa at 20 degrees C reverses the inhibition. The use of hydrostatic pressure to control the activity of lambda exonuclease has potential practical application in DNA sample preparation, analysis, and sequencing.
O2 uptake in the lungs, and therefore arterial oxygenation, is favored by a low Hb-P50 but this inhibits tissue O2 extraction, raising the question of optimal P50 during maximal exercise when VO2 is limited by O2 supply. Using a model of the lungs and muscles connected by the circulation so that O2 transport is simultaneously considered in both sites, sensitivity of VO2max to P50 was determined at three altitudes: PB = 760, 464 and 253 Torr, encompassing sea level and Mt. Everest. At Pb = 760 Torr, VO2max peaked at P50 = 30 Torr, was 99.4% (of that at 30) at normal P50 (26.8) and exceeded 95% (of that at P50 = 30) over the P50 range from 24 to 43 Torr. Optimal P50 at PB = 464 Torr was 25 Torr, VO2max at P50 = 26.8 was reduced only 0.1% and exceeded 95% over the P50 range from 19 to 41 Torr. At Pb = 253, optimal P50 was 20 Torr, VO2max at P50 = 26.8 was reduced only 0.4% and exceeded 95% over the wide P50 range from 15 to 47 Torr. While this analysis shows that technically, optimal P50 falls with altitude, VO2max is insensitive to P50 over a range that widens with altitude, so that P50 changes over a realistic interval would not measurably affect VO2max.
The formation of plaques by lambda phage in Escherichia coli was prevented by elevated hydrostatic pressure; phage plaques were not detected at 30 MPa. Furthermore, using promoter fragments derived from the malB operon, we showed that gene expression initiated from both promoters (malK-lamB and malEFG) was repressed by elevated hydrostatic pressure. Our findings suggest that high pressure affects gene expression directed by the malB regulatory interval, and this may cause a decrease in the quantities of lambda receptor protein, LamB.