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  • Title: Deoxyribonucleic acid modification methylase from Bacillus stearothermophilus.
    Author: Levy WP, Welker NE.
    Journal: Biochemistry; 1981 Mar 03; 20(5):1120-7. PubMed ID: 7225321.
    Abstract:
    A modification methylase was isolated from Bacillus stearothermophilus 1503-4R (Bst 1503I) and purified to homogeneity. The enzyme is an acidic protein and composed of a subunit with a molecular weight of 105 000, and only the tetrameric form was detected in solution. The methylase exhibited maximal activity between 54 and 61 degrees C and between pH 8.1 and 9.3. In contrast to Bst 1503I endonuclease [Catterall, J.F., & Welker, N. E. (1977) J. Bacteriol. 129, 1110-1120], the methylase is completely inactivated when exposed to temperatures near the optimal growth temperature (63-67 degrees C). The methylase was also inactivated when exposed to temperatures below the minimal growth temperature (48-53 degrees C). The thermostability of the methylase is significantly enhanced by Na+, K+, or NH4+. Membrane-bound methylase is resistant to heat inactivation at temperatures near the maximum growth temperature (73-75 degrees C). The methylase functions as a tetramer. The initial rates of methyl transfer are first order in methylase concentration, and the enzyme obeys Michaelis-Menten kinetics with respect to DNA but not to S-adenosyl-L-methionine.
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