Studies in immunochemistry. 11. The action of dilute alkali on the N-acetylhexosamines and the specific blood-group mucoids

Publisher Website
Google Scholar
Abstract
Conditions for the colorimetric detn. of N-acetylhexosamines were reinvestigated. The period of heating necessary, and the max. amt. of color obtained, when N-acetylglucosamine is treated with alkali and the p-dimethylaminobenzaldehyde reagent, depends not only on the pH of the system but also on the nature of the buffer employed. Borate buffer gives an enhanced color production. N-Acetyl-chondrosamine behaves similarly, but the intensity of the color given is about 23% of that obtained with an equal weight of N-acetylglucosamine. The N-acetylhexosamines after treatment with alkali show a single max. absorption at 230 m[mu] and after the addition of the p-dimethylaminobenzaldehyde reagent the purple color which develops shows 2 absorption max., at 550 and at 590 m[mu]. A mixture of glucose and lysine heated with Na2CO3 shows no characteristic absorption max. at 230 m[mu]. The purple color obtained on the subsequent addition of p-dimethylaminobenzaldehyde reagent shows a single absorption max. at about 560 m[mu]. The human blood-group mucoids yield between 7 and 10% of the color intensity given by an equal wt. of N-acetylglucosamine, and there is no enhanced color production when a borate buffer is employed. The absorption characteristics of the chromogenic substances which arise from the group substance after heating with alkali, and of the colored product obtained on the addition of the p-dimethyl-aminobenzaldehyde reagent support the belief that the color given by the group substances arises from reducing N-acetylchondrosamine end groups and closely linked N-acetylglucosamine residues, which are readily liberated by the action of alkali. The A substance, after oxidation with hypoiodite, gives rise to a colored complex on treatment with alkali and p-dimethylaminobenzaldehyde which shows a reduced absorption intensity compared with that given by the unoxidized material. A substance oxidized with periodate and treated under similar conditions shows no decrease in absorption. The significance of these findings is discussed.