Concentration effects in assays of sheep liver mitochondrial aldehyde dehydrogenase and their interpretation in terms of enzyme dissociation.

Enzyme assays exhibit lag-phases during which the rate of acetaldehyde oxidation or p-nitrophenylacetate hydrolysis accelerates. A steady-state rate is achieved, but the time taken for this to occur increases as the enzyme concentration is decreased. With 0.009 microM enzyme this takes about 15 minutes. Analysis of experimental results suggests that the activation occurs because the tetrameric enzyme dissociates to a more active species. Gel filtration behaviour of the enzyme at different concentrations and stability tests with urea provide some general support for this hypothesis.