Graduate Thesis Or Dissertation
 

The purification and characterization of the fructose-1, 6-diphosphate aldolase from Bacillus stearothermophilus (NCA 2184)

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  • The thermophilic aldolase from Bacillus stearothermophilus (NCA 2184) has been purified to a specific activity of 45.5 μ-moles of fructose-1, 6-diphosphate cleaved per minute per mg of enzyme, representing a 624-fold increase over the crude extract. The preparation appeared to be homogenous by sedimentation velocity ultra-centrifugation and by a specific constant activity across the protein peak on Sephadex G-200. However, a trace amount of triose-phosphate isomerase was detectable. The purified enzyme was determined to be a Type II aldolase on the basis of its metal ion (Mn⁺⁺) and sulfhydryl requirements, its narrow pH optimum, and its resistance to carboxypeptidase-A treatment and sodium borohydride reduction in the presence of substrate. The K[subscript m] (1.1 x 10⁻⁴ M) and V[subscript max] (4650 moles of substrate cleaved per minute per mole of enzyme) were found to be similar to other Type H aldolases. The molecular weight was found to be about 58,000 by sedimentation equilibrium ultracentrifugation and the uncorrected S₂₀ value was found to be 4.25. Values for the Q₁₀ and Arrhenius activation energy were found to be 2.2 and about 16,000 calories per mole, respectively. The amino acid composition of the aldolase was found to be similar to those reported for other thermophilic proteins, although there are distinct differences. Comparison of this aldolase's hydrophobicity with that of a relatively heat-labile yeast aldolase indicates that the content of hydrophobic amino acids cannot be correlated to the relative thermostability of this enzyme. This suggests that the hydrophobicity parameter is not an adequate explanation for the thermostability of thermophilic proteins.
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