The synthesis of aldehydes from carboxylic acids is a challenge that the enzyme carboxylic acid reductase (CAR) is mastering. The R-domains of CARs, however, can additionally catalyze carbonyl reduction. This activity is a minor side reaction for many substrate/enzyme pairs but may be significant for others.

Abstract

Carboxylic acid reductase enzymes (CARs) are well known for the reduction of a wide range of carboxylic acids to the respective aldehydes. One of the essential CAR domains - the reductase domain (R-domain) - was recently shown to catalyze the standalone reduction of carbonyls, including aldehydes, which are typically considered to be the final product of carboxylic acid reduction by CAR. We discovered that the respective full-length CARs were equally able to reduce aldehydes. Herein we aimed to shed light on the impact of this activity on aldehyde production and acid reduction in general. Our data explains previously inexplicable results and a new CAR from Mycolicibacterium wolinskyi is presented.