lawnchairskank - 14-12-2009 at 23:51
Can sugars denature enzymes? Could the aldehyde/ketone group bond to an amino group and mess with the way an enzyme is folded? What would be the most
reactive sugars? Thanks
JohnWW - 15-12-2009 at 00:17
I have not heard of ordinary sugars on their own denaturing enzymes. Enzymes are usually denatured by high heat, about 100ºC, or by strong mineral
acids or alkalis or oxidants. The most reactive ordinary sugars (i.e. not containing highly reactive unnatural substituents) would be the oxidized
ones containing carboxylic acid groups, like tartaric or gluconic acids, noting also that they occur in optically active enantiomers which would react
differently with enzymes.
lawnchairskank - 15-12-2009 at 08:58
Thanks.
chemoleo - 15-12-2009 at 17:40
There are rather rare occurrences, however, when the aldehyde/ketone group reacts with other groups in the protein (i.e. lysines).
Unfortunately this will require detailed scrutiny of the literature for details. But generally sugar groups are fairly benign.
Nonetheless, sugars will undoubtedly affect the way proteins fold, as I recall >50% of all proteins are glycosylated - you go and figure as to the
importance of glycosylation. (if there was no reason for glycosylation to evolve, it wouldn't have - therefore it has a significant role)
Enzymes (like any other protein) denature depending on their own properties- sometimes a 5 deg C temperature rise is enough, sometimes (as with
thermostable (thermophile) enzymes) they are most active at high temperatures. This is altogether quite empirical- as transfering the properties of
one enzyme to another with reasonable sequence identity doesn't mean at all that it will behave the same way.
Ozone - 15-12-2009 at 17:52
Which "sugar" so you mean?
Sucrose, for example, does not denature proteins (enzymes) so far as I know. In fact, it can prevent (e.g. stabilize) the denaturization of protein
that can result from extremes of pH and/or temperature (or complexes with various metal ions).
For example, when acidified, BSA (bovine serum albumin) precipitates from solution. This does *not* occur if there is ~5% or more of sucrose present
in the solution. Sucrose has also been demonstrated to increase the thermostability of protein (I can forward references if desired).
This is why most commerical enzyme preparations include sucrose in the mix.
Reducing sugars, however, can (slowly) react with the terminal (e.g. N-e-NH2-) of lysine and/or arginine to yield glycated products (pentosidine
dimers, etc.). This can lead to the crosslinking of proteins such as collagen, in-vivo. The term Advanced Glycation Endproducts (AGEs) seems
appropriate as the reaction is implicated in the aging process. See also the "Maillard reaction". Similar behavior has been noted in rat tendon
in-vitro.
See diabetes specifically. Uncontrolled glucose/fructose in the blood glycates, crosslinks and hardens arteries, eye lenses, etc to where a 21
year-old uncontrolled diabetic chemically resembles a 70+ year old.
Cheers,
O3
[Edited on 16-12-2009 by Ozone]