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Determination of N-Acetylglucosamine-1-Phosphate and N-Acetylglucosamine in Milk¹

Department of Nutrition, Food Science and Technology, Massachusetts Institute of Technology, Cambridge

ABSTRACT

It was reported recently (1) that cow milk contains greater amounts of N-acetylglucosamine-1-phosphate (NAGA-P) than, of any other acid-soluble organic phosphate (9 mg/100 ml were isolated). Although the physiological role of this compound and the significance of its occurrence in milk have not yet been established, a convenient method for its determination would appear to be of interest.

To 10 ml milk, add 10 ml of water and enough hydrochloric acid (approx. 0.3 ml N HCl) to precipitate the casein. Centrifuge the mixture immediately and decant the supernatant solution.

Determine free N-acetylglucosamine (NAGA) according to Reissig et al. (2) as follows:

To 0.3 ml of the clear serum add 0.2 ml of water and 0.1 ml of 0.8 M potassium tetraborate which has been brought to pH 9.1 with KOH, and heat the mixture for 3 min at 100 C. After cooling, add 3 ml of p-dimethylaminobenzaldehyde (DMAB) reagent. [The DMAB reagent is prepared by dissolving 10 g of DMAB in 100 ml of acetic acid (glacial) containing 12.5% (v/v) 10 N HCl. The resulting solution is diluted with nine volumes of acetic acid before use.]

¹ From the Ph.D. thesis of the author, Massachusetts Institute of Technology.

² Present address: American Meat Institute Foundation, University of Chicago, Chicago, Illinois.