Optimum substrate size and specific anomer requirements for the reducing-end glycoside hydrolase di-N-acetylchitobiase. 
Di-N-acetylchitobiase is a family 18 glycoside hydrolase that splits the reducing-end GlcNAc from chitooligosaccharides.  The enzyme hydrolyzed only the alpha-anomer of five tested substrates, chitin di- through hexasaccharide.  In all cases the glycosyl fragment retained its beta-configuration while the split monosaccharide was alpha-D-GlcNAc.  Chitobiose was hydrolyzed less than half as fast as the other larger substrates.  All four of them, tri- to hexasaccharide, reacted at the same rate.  The biochemical behavior of di-N-acetylchitobiase indicates it has three subsites, -2, -1, +1, in which the reducing-end trimer of any sized chitooligosaccharide is bound.  The +1 site is specific for an alpha-anomer.