Studies on Chitin II. Reaction of N-Acetyl-D-Glucosamine With a-Amino Acids, Peptides, and Proteins

Abstract

The reaction of N-acetyl-D-glucosamine with a-amino acids, peptides, and proteins has been investigated. The course of the reaction has been followed by methods which involved the use of paper partition chromatography, polarimetric measurements, measurement of pH depression, and equilibrium dialysis. It is considered that products of the Schiff base (or azomethine) type are formed but the combination is unstable and is split even in the biological pH range. No reaction occurs under acidic conditions but ~der alkaline conditions the amount of reaction increases with the pH. At a given pH the percentage combination depends upon the equilibrium constant of the reaction and upon the dissociation constant of the a-amino nitrogen, as this determines the initial concentration of the reagent. Differences in the degrees of ionization are more important in determining the percentage combination than are the differences in the equilibrium constants. The reaction is of a similar type to that which occurs between glucose and a-amino acids or peptides. Tyrosine, as well as free a-amino groups, appears to play an important part in the binding of N-acetyl-D-glucosamine by insect cuticular proteins. 2-Acetamido-2-deoxyN'- D-glucosylglycine ethyl ester has been synthesized from N-acetyl-D-glucosamine and glycine ethyl ester and its properties have been investigatd.