Oct 21, 1975

The role of bound calcium ions in thermostable, proteolytic enzymes. I. Studies on thermomycolase, the thermostable protease fron the fungus Malbranchea pulchella

G Voordouw, R S Roche


Thermomycolase, the thermostable, extracellular, serine protease of the fungus Malbranchea pulchella (G. Voordouw, G. M. Gaucher, and R. S. Roche (1974), Can J. Biochem. 52, 981-990), binds one calcium ion with an apparent binding constant of 5 X 10(5) M-1 at 25degreesC, pH 7.50, and ionic strength 0.1. There is very little change in the overall conformation of thermomycolase upon binding of this calcium ion: no change can be detected, beyond experimental error, in the sedimentation coefficient or the aromatic and peptide circular dichroism of the enzyme. However, binding of calcium changes the absorption spectrum, the ultraviolet difference spectrum being characterized by a strong band at 237 nm and smaller bands at 280 and 295 nm. The difference molar extinction coefficient at 237 nm parallels the calcium-binding isotherm. The small changes in equilibrium properties are constrasted by large calcium-dependent changes in the rates of autolytic degradation and thermal and urea denaturation. The dependence of the second-order rate constant for autolytic degradation on the free calcium ion concentration can be quantitatively accounted for by a model in which only conformers with an unoccupied calcium binding site serve as substrat...Continue Reading

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Mentioned in this Paper

Frontal Part of Head
Calcium [EPC]
Malbranchea pulchella
Peptide Hydrolases
Filamentous fungus
Calcium ion

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