Naofumi Takahashi

Adhesion of human cancer cells to vascular endothelium mediated by a carbohydrate antigen, sialyl Lewis A.

Recently the lectin-like domain on ELAM-1 (endothelial leukocyte adhesion molecule-1) was shown to recognize a carbohydrate antigen, sialyl Lewis x. In this paper we demonstrate, by a series of inhibition experiments utilizing specific monoclonal antibodies and pure glycolipid preparations, that the sialyl Lewis a antigen serves as a specific ligand for ELAM-1 as well as sialyl Lewis x and plays a significant role in the ELAM-1-mediated binding of human cancer cells to activated endothelial cells.

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

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 0.1 µm, 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,...

Enzymatic Improvement of Food Flavor II. Removal of Beany Flavor from Soybean Products by Aldehyde Dehydrogenase

Aldehyde dehydrogenase catalyzes the irreversible conversion of aldehydes into their corresponding acids. NAD-dependent aldehyde dehydrogenase purified from bovine liver mitochondria was used to remove the green beany flavor of soybean products. Incubation of the enzyme, in the presence of NAD+, with defatted soybean extracts or with soybean milk, resulted in the almost complete disappearance or in a great reduction of the flavor. It was found from experiments with pyrazole, an inhibitor of alcohol dehydrogenase, was used, that alcohols contributing to the beany flavor were converted into acids by the cooperative action of alcohol dehydrogenase and aldehyde dehydrogenase. The protein isolate prepared from the soybean extract after treatment with these enzymes produced no substantial beany flavor after storage in powdered form. Aldehyde dehydrogenase improved flavor in extract of mutton.

Enzymatic Improvement of Food Flavor IV. Oxidation of Aldehydes in Soybean Extracts by Aldehyde Oxidase

Aldehyde oxidase (aldehyde: oxygen oxidoreductase, EC 1.2.3.1) was partially purified from bovine liver. The enzyme irreversibly oxidized various aldehydes to the corresponding acids by using dissolved oxygen as an electron acceptor. Although the Km value for n-hexanal was low (6 µm), that for acetaldehyde was high (20 mm).Medium-chain aldehydes such as hexanal and pentanal appear to be mainly responsible for green beany odor of soybean products. A great reduction in the beany odor was observed after the soybean extract was incubated with aldehyde oxidase under aerobic conditions. Dissolved oxygen was utilized as the electron acceptor throughout the enzyme-catalyzed oxidation of aldehydes and none of other cofactors were found to be required.It has been shown that bovine liver mitochondrial aldehyde dehydrogenase oxidizes the soybean protein-bound aldehyde with a rate comparable to that for free n-hexanal (Agric. Biol. Chem., 43, in press). Comparative studies of aldehyde oxidase and aldehyde dehydrogenas...

Enzymatic Improvement of Food Flavor III. Oxidation of the Soybean Protein-Bound Aldehyde by Aldehyde Dehydrogenase

Defatted soybean extract was fractionated into protein fractions and low molecular weight fractions with gel filtration. NAD-dependent aldehyde dehydrogenase from bovine liver mitochondria and from yeast was found to oxidize aldehyde in both fractions. These enzymes, therefore, were used to determine the quantity of aldehyde. When the protein fraction obtained by gel filtration was subjected to gel filtration again, aldehyde was recovered in the protein fractions. The level of aldehyde in the protein fractions was unchanged before and after digestion of the protein with pepsin. When the soybean extract was incubated beforehand with aldehyde dehydrogenase and NAD+ and the subjected to gel filtration, no aldehyde was detected in the protein fractions. These results indicate that aldehyde dehydrogenase acts on the soybean protein-bound aldehyde. Alcohol dehydrogenase from horse liver in the presence of NADH did not convert the bound aldehyde to alcohol.A large portion of the aldehyde in the extract was separ...