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) has been purified to homogeneity by conventional purification procedures. The enzyme was found to have a molecular weight of 215, 000 based on gel filtration. The protein is composed of polypeptides having the same molecular weight, 54, 000 and thus it appears to consist of four 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 0.1μM, and relatively constant independent of the carbon 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°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 three 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.

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