Enzymatic Improvement of Food Flavor I. Purification and Characterization of Bovine Liver Mitochondrial Aldehyde Dehydrogenase

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Abstract
Bovine liver mitochondrial aldehyde dehydrogenase (aldehyde: NAD+ oxidoreductase, EC 1.2.1.3) was purified to homogeneity by conventional purification procedures. The enzyme was found to have a MW of 215,000 based on gel filtration. The protein is composed of polypeptides having the same MW 54,000 and it appears to consist of 4 subunits of equal size. The enzyme exhibited a broad aldehyde specificity, oxidizing irreversibly a wide variety of aliphatic and aromatic aldehydes to corresponding carboxylic acids. Km values for straight-chain saturated aldehydes were below 0.1 .mu.M and relatively constant independent of the C chain lengths of the aldehydes. The maximum velocities for saturated aldehydes also did not vary appreciably with their carbon chain lengths. Maximum activity was observed at pH 9.3 and 50.degree. C. The enzyme activity was affected by some divalent cations. Ca2+ enhanced the activity, while Mg2+ inhibited it. The enzyme was quite stable at neutral pH, but was unstable above pH 9 or below pH 6. Bovine liver has 3 isozymes of aldehyde dehydrogenase which are located in the mitochondrial, cytosolic and microsomal fractions. Comparison of enzymic properties among these isozymes and yeast enzyme indicates that the mitochondrial enzyme is very suitable for improving the objectionable flavor due to aldehydes in foods.