MOLECULAR BASIS OF BIOLOGICAL STABILITY TO HIGH TEMPERATURES

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Abstract
One plausible explanation for the ability of thermophilic organisms to grow at temperatures usually lethal to other organisms is that they possess relatively heat-stable proteins. Flagella from thermophilic bacteria are much more stable than similar structures from mesophilic bacteria. Since flagella are organized aggregates of fibrous proteins, this relative stability probably is a reflection of the forces holding these molecules together. The relative stability of flagella appears to be an intrinsic property of these structures; no stabilizing or labilizing materials could be demonstrated. Thermophile flagella are also more stable than mesophile flagella in the presence of urea and acetamide, agents regarded as hydrogen-bond breakers, and of sodium dodecylsulfate, an anionic detergent. These findings are interpreted to mean that the relative stability of thermophile flagella is due to more numerous, stronger, or more strategically located hydrogen and/or hydrophobic bonds than are present in mesophile flagella. The latter seem to contain twice as many titratable groups as do the former. This suggests that under certain circumstances they might be under greater stress, created by the repulsion between charged groups having like signs.

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