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Cellular and Tissue Injury During Nonfreezing Cold Injury and Frostbite.

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Triannual rept. no. 4, Jan-Apr 92,

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Metabolic perturbation studies. We have completed a detailed statistical analysis of our metabolic heat rate and cross-over point data for red blood cells. Both data sets support the original hypothesis that the degree of protonation, not pH per se, determines the relative activity of the enzymes in a metabolic pathway. This work and related studies with microcalorimetry will be presented at the 1992 International Meeting of the Society for Cryobiology Abstracts enclosed. Analysis of the data from microcalorimetric experiments involved comparison of Q10 i.e., change in rate due to a 10 deg C change in temperature values for metabolic heat rates under conditions of constant pH pH stat vs. alphastat conditions. Alphastat means that the degree of protonation of alpha imidazole in histidine residues is maintained constant as temperature is varied. Histidine is the only amino acid in enzymes that has a pK. in the physiological pH range. In our red cell model, this is accomplished by allowing intracellular pH to increase, as temperature is lowered, to the same degree that histidine pKa increases. The theory predicts that Q10 should be higher for biological rate functions under pH stat than under alpha stat conditions. This is because under pH stat the degree of protonation of histidine residues increases as temperature is lowered. For our data, Q10 for metabolic heat which in red cells is predominantly due to glycolytic flux under pH stat was larger for all pairs of measurements compared to the alphastat pairs of measurements, over the same temperature range. This trend was statistically significant at the p 0.05 level by the paired students t test. These data represent the first in vivo demonstration

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  • Biochemistry
  • Anatomy and Physiology
  • Medicine and Medical Research

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