Breaks in arrhenius plots of reactions involving membrane-bound and solubilized sialyltransferases, due to temperature dependence of kinetic parameters.

Temperature dependence of asialomucin-sialyltransferase (CMP-N-acetylneuraminate:D-galactosyl-glycoprotein N-acetylneuraminyltransferase, EC 2.4.99.1) activity is investigated. Discontinuities in Arrhenius plots are observed, whether the enzyme is membrane-associated or solubilized. These discontinuities cannot be firmly correlated with the phase-transition temperatures of either endogenous or exogenous phospholipids. Arrhenius plots of the kinetic parameters also exhibit sharp discontinuities, so that it is concluded that a significant change in Km and Vmax values occurs with varying temperature. Our results suggest that the biphasic behavior of Arrhenius plots may be attributed to the temperature dependence of the kinetic parameters for both membrane-associated and solubilized sialyltransferase activities.