June 16, 2003
Volume 81, Number 24
CENEAR 81 24 p. 8
ISSN 0009-2347


Mass spec method distinguishes isomers of complex sugar building blocks


Carbohydrates are among the toughest biological molecules to characterize structurally. The type of carbohydrates known as glycosaminoglycans (GAGs), such as heparin and heparan sulfate, are particularly difficult because they are highly charged and have many possible isomers.

A sensitive new method for characterizing these complex sugars now has been added to the chemist's toolbox. Graduate student Ola M. Saad and adjunct chemistry professor Julie A. Leary at the University of California, Berkeley, use electrospray ionization mass spectrometry (ESI-MS) to identify and quantify isomers of the disaccharides that make up heparin and heparan sulfate [Anal. Chem., 75,
2985 (2003)].

First, enzymes digest the polysaccharides into their component disaccharides. Then the complex mixtures are analyzed by ESI-MS without further separation or purification steps. Using an internal standard and a calculated response factor, Saad and Leary quantitate the disaccharide composition of heparins and heparan sulfates in a variety of samples.

Leary plans to use the method to elucidate structure-function relationships in these sugars. "People are just beginning to look at the extracellular matrix and look at the components of the glycosaminoglycans to try to relate their structure with their function," she says. "Without knowing exactly which disaccharides and which isomers are there, you're never going to be able to get structure-function relationship."

"If you're looking at a particular cell or tissue, it's very important to capture all the different building blocks and quantitate them," says Ram Sasisekharan, professor of biological engineering at MIT. "To be able to do that in a fairly integrated way using ESI-MS is an important advance for the field."


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