Summary: The metabolism of various organic substrates by suspensions of subsp. in a salts solution was followed by microcalorimetry. Enthalpy changes associated with metabolism were in good agreement with theoretical values. Substrate utilization showed Michaelis kinetics, allowing saturation constants ( ) and maximum specific rates of substrate utilization ( ) to be determined. In cells grown on a complex medium containing glucose, values were: glucose, fructose, -acetylglucosamine, glycerol and pyruvate, <5 μ;M; lactate, 20 μ;m; glucosamine, 130 μ;m, and mannose, 1 mM. Values of for glycerol, pyruvate and lactate were similar and approximately twice those for glucose, mannose, glucosamine and -acetylglucosamine; for fructose was one-quarter of that for glucose. In cells grown on complex medium in which glucose was replaced by mannose, glucosamine or -acetylglucos-amine, and for the respective growth sugars and for glucose were not significantly affected. However, in cells grown in the presence of fructose, for fructose increased to the value observed for glucose. It is suggested that is adapted to, and is constitutive for, the utilization of a single sugar (glucose), and a single amino sugar (-acetylglucosamine), but that in the presence of fructose a fructose-utilizing pathway is induced.


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