Abstract
Exposure of methylotrophic yeasts to other carbon sources after growth on methanol results in catabolite inactivation. As a result, peroxisomes are rapidly degraded effectively disabling the metabolic pathway initiated by alcohol oxidase in favour of a more energetically favourable route. A model equation has been developed to describe the effect of temperature, dissolved oxygen concentration and acetaldehyde (catabolite) concentration on catabolite inactivation in Pichia pastoris. When pre-exposed to 4 g/l acetaldehyde at 30°C, the rate of conversion of ethanol to acetaldehyde decreased by 75%. Inactivation was reduced to 45% at 30°C by reducing the dissolved oxygen concentration. At high dissolved oxygen concentration, enzyme function was only inactivated by 20% if the temperature during the period of exposure to acetaldehyde was reduced to 5°C. The influence of acetaldehyde can be eliminated completely by operating at 5°C and low dissolved oxygen concentrations. Application of these findings to process design has enabled us to conduct preliminary reactions in laboratory-scale reactors that have yielded acetaldehyde concentrations greater than 3 M (130 g/l) in 4 h.
Published Version
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