Interaction of alpha-amylase with n-alkylammonium bromides

The interaction of alpha -amylase with n-alkylammonium bromides above and b elow their critical micellar concentrations (cmc) has been studied in buffe r at pH 7 and 10 by UV spectrophotometry, photon correlation spectroscopy a nd Doppler microelectrophoresis. This interaction produces a complex that i s dependent on pH of the medium. This complex appears at surfactant concent rations below the cmc, which means that individual surfactant molecules can bind lightly to native alpha -amylase. The complex maintains its aggregati on state when the concentration of surfactants with a hydrocarbon chain of 16 carbons increases. but not for surfactants of 12 and 14 carbons. Measure ments of zeta -potential indicate the influence of electrostatic and hydrop hobic forces. When the size of the aggregate is maximal, proteins are at th eir point of zero charge. In such conditions, Van der Waals forces and cont acts between the alkyl chain and the hydrophobic core of the protein favour the formation of a larger aggregate. (C) 2001 Elsevier Science B.V. All ri ghts reserved.