Penicillium camemberti galacturonate reductase: C-1 oxidation/reduction of uronic acids and substrate inhibition mitigation by aldonic acids

• Published in: International journal of biological macromolecules Vol. 153; pp. 1090 - 1098
• Main Authors: Wagschal, Kurt, Jordan, Douglas B., Hart-Cooper, William M., Chan, Victor J.
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 15-06-2020
• Subjects: Aldaric acid; Aldonic acid; Amino Acid Sequence; Enzyme Stability; Food waste; Galacturonate reductase; NAD (+) and NADP (+) Dependent Alcohol Oxidoreductases - antagonists & inhibitors; NAD (+) and NADP (+) Dependent Alcohol Oxidoreductases - chemistry; NAD (+) and NADP (+) Dependent Alcohol Oxidoreductases - metabolism; NADP - metabolism; Oxidation-Reduction; Penicillium - enzymology; Substrate inhibition; Sugar Acids - pharmacology; Temperature; Uronic Acids - metabolism; Food waste; Aldaric acid; Substrate inhibition; Aldonic acid; Galacturonate reductase
• ISSN: 0141-8130; 1879-0003
• DOI: 10.1016/j.ijbiomac.2019.10.239

The enzyme galacturonate oxidoreductase PcGOR from Penicillium camemberti reduces the C-1 carbon of D-glucuronate and C-4 epimer D-galacturonate to their corresponding aldonic acids, important reactions in both pectin catabolism and ascorbate biosynthesis. PcGOR was active on both glucuronic acid and galacturonic acid, with similar substrate specificities (kcat/Km) using the preferred co-substrate NADPH. Substrate acceptance extended to lactone congeners, and D-glucurono-3,6-lactone was converted to L-gulono-1,4-lactone, an immediate precursor of ascorbate. Reaction with glucuronate showed only minor substrate inhibition, and the product L-gulonate and L-gulono-1,4-lactone were both found to be competitive inhibitors with Ki in the low mM range. In contrast, reaction with C-4 epimer galacturonate displayed marked substrate inhibition. Moreover, the product L-galactonate and L-galactono-1,4-lactone were observed to mitigate substrate inhibition by galacturonate, with the lactone having a greater effect than the acid.