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Specific Viscosity for Glycoaminoglycans

Paul Dubin dubin at chem.iupui.edu
Fri Oct 24 05:23:05 EST 2003


> Dana Summers wrote:
> 
> In reading older articles pertaining to glycoaminoglycans
> (mucopolysaccharides) (dermatan sulfate, chondroitin sulfate and
> keratan sulfate) I see some articles talk about  specific viscosity
> values using an Ostwald viscometer. The question I have is what part
> of the molecule contributes to the increase or decrease of
> its viscosity? Is it the D-glucuronate or L-iduronate
> (uronic molecules) or is it the N-acetylgalactosamine or
> N-acetylglucosamine (disaccharide units), or is it the core proteins
> that these molecules are attached to? The reason I ask is a researcher
> may treat the mucopolysaccharide one way and obtained one viscosity
> value and then treated it another way and received a higher or lower
> viscosity value compared to the previous run. What changed to change
> its viscosity?
> Dana
The old name of "mucopolysaccharides" as far as I know refers to
proteoglycans, which at that time were poorly understood. GAGs means the
polysaccharide component of proteoglycans such as the ones you list. So
GAGs should not have core proteins. If they do, they are not GAGs, they
are PGs.

These (GAGs) enormously charged and extremely hydrophilic polymers
should be so well soluble that the properties of their solutions should
not be dependent on time, stirring etc. 

The viscosity is a property of the entire polymer chain, so it doesn't
make sense to ask "what part of the molecule" contributes to the
viscosity. Since these are highly charged polymers i.e.
polyelectrolytes, their viscosities depend not only on the concentration
of the solution and the temperature, but also very strongly on the ionic
strength. However, for a fixed ionic strength and temperature, the
intrinsic viscosity -- the important parameter for characterizing the
molecule -- should not vary from one trial (or lab) to another (for a
given sample).
However, it will be strongly MW-dependent, so samples of e.g. DS of
different MWs will have proportionally different IV's. And of course, no
one has a very good handle on the chemical polydispersity of any of the GAGs.

As far as I know, the only thorough study of GAG IV is an old one by
Stivala on heparin. I'd be curious to know if such thorough studies have
been done on any of the other GAGs you mention.

Paul Dubin




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