Stabilization of NAD(+)-dependent dehydrogenases and diaphorase by bilayer encagement

A feasibility study aimed at stabilization of L-lactate-dehydrogenase, L-malate-dehydrogenase, alcohol-dehydrogenase and diaphorase by the recently described method of enzyme 'encagement' was conducted. This method involves derivatizing the enzymes with polyglutaraldehyde, followed by secondary crosslinking with amino derivatives of polyacrylamide. Encagement conditions were optimized for each of the four enzymes, so as to achieve the highest thermal stability combined with highest catalytic activity. Depending on the encagement conditions, residual activities were in the range of 18% to 96% with higher values in the presence of cofactors. Increases in thermal stabilization of up to 26-fold were obtained. For high retention of enzymic activity and stability, the most significant factor was the concentration of polyglutaraldehyde; the crosslinking polymers had only a negligible effect. Furthermore, the significant enhancement in thermal stability could be attained without perturbing the kinetic parameters: Km values for NADH and pH optima remained unaltered for the stabilized enzymes.