Abstract
Initial rate kinetics of dextran synthesis by dextransucrase (sucrose:1,6α- D-glucan-6-α- D-glucosyltransferase, EC 2.4.1.5) from Leuconostoc mesenteroides NRRL B-512F showed that below 1 mN, Ca 2+ activated the enzyme by increasing V max and decreasing the K m for sucrose. Above 1 mM, Ca 2+ was a weak competitive inhibitor ( K i = 59 mM. Although it was an activator at low concentration, Ca 2+ was not required for dextran synthesis, either of main chain or branch linkages. Neither was it required for sucrose hydrolysis, acceptor reactions, or enzyme renaturation after SDS-polyacrylamide gel electrophoresis. A model for dextran synthesis is proposed in which dextransucrase has two Ca 2+ sites, one activating and one inhibitory. dextran synthesis is proposed in which dextransucrase has two Ca 2+ sites, one activating and one inhibitory. Ca 2+ at the inhibitory site prevents the binding of sucrose.
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