[Doc Holliday]

Reducing end sugars in oligosaccharides are capable of ring opening and are in equilibrium between furanose/pyranose structures as well as interconverting between alpha/beta, different chair conformers, etc. in solution correct? 

Sialic acid often caps proteoglycans and is a non-reducing sugar. However I just read this paper tonight that describes the mutarotation mechanism for sialic acid:

http://www.ncbi.nlm.nih.gov/pubmed/21584336

The mechanism is different than the typical ring opening mechanism for a reducing sugar where the -O next to the anomeric carbon is first protonated.  Does this mean that the sialic acid residues at the ends of oligosaccharides are still capable of undergoing mutarotation in solution even though the -OH on their anomeric carbon has a glycosidic bond?  This would contrast to a typical reducing sugar that is prohibited from ring opening once it has a glycosidic bond on its anomeric carbon would it not?