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A number of long chain N-acyl-glycines, N-acyl-DL-serines, and N-acyl-DL-cysteines have been synthesized by means of the mixed anhydride method. The critical micelle concentrations of the sodium salts of these compounds have been determined with the dye method. These values in the cysteine series are only half as high as in the glycine and serine series, i.e. the micelles of the cysteine derivatives are more stable. From these observations one may conclude that the cysteine side chain participates in the hydrophobic bonding system of the micelle. Moreover, the quantitative comparison of the values of the critical micelle concentrations leads to the conclusion that the CH2SH group has the same effect, on the micelle stability as a methylene group of the hydrocarbon tail of the compounds investigated. Therefore, there is justification for the recently voiced assumptions of the hydrophobic nature of the cysteine side chain in proteins. [ABSTRACT FROM AUTHOR]

The activation of Escherichia coli K12 3300 β-galactosidase by Na+ and Mg2+ ions appears to involve, apart from effects on the catalytic rate, a complex pattern of interaction between the substrate and the two cations. The time course of activation by Mg2+ can be followed directly by rapid mixing methods; m the presence of Na+ the kinetics of this process is complex, due to the presence of a monomolecular step which becomes rate limiting at high reagent concentrations. The effects produced by Na+, on the other hand, occur rapidly in comparison with the highest attainable rates of catalysis. The activity of defective enzymes from lac- point mutants is also Na+- and Mg2+-dependent. [ABSTRACT FROM AUTHOR]