Oxygen Induced Transformation of the NADH-Nitrate Oxidoreductase from Bacillus Stearothermophilus

Abstract

The elusive character of the basis for heat stability of proteins in thermophilic organisms is universally acknowledged. Thermophiles appear to beat the high cost of faster metabolic rates by high turnover of many intracellular components including certain enzymes (2). A lower level of dissolved oxygen is also a fact of life at elevated temperatures. In many types of procaryotes, denitrification is a useful alternative to limited atmospheric oxygen. There may be appreciable selective pressure for retention of nitrate respiration among thermophilic microorganisms as a prime energetic expedient. The postulated mechanisms whereby bacteria continually adjust their enzymatic composition to cope with a variable environment are increasing in number and complexity. Among the most important of these is the manner in which the cell recognizes and responds to continually varying levels of available terminal oxidant whether it be oxygen, nitrate, nitrite, thiosulfate, sulfite or tetrathionate.