Martin Dalziel wrote:
>> Dear Glyco-netters,
>> Various soluble glycosyltransferases are found in serum, colostrum,
> saliva, etc...
>> I am curious to find out what the consensus of opinion is as to what the
> function(s), if indeed there are any, of these forms of the
> glycosyltransferases might be.
>> For example, is transferase activity impossible due to the scarcity of
> nucleotide-sugar substrates? Can they still bind to target
> oligosaccharide sequences, without transferase activity, in a lectin
> like manner? or are they simply unwanted secreted cellular products?
many people think proteolytic cleavage of the stem region of a glycosyltransferase is
a "turnover" mechanism by which cells get rid of glycosyltransferases in order to
down-regulate their activity inside of a cell. the secretep portion is active in a
tube where you provide enough substrate, but may not be active as an enzyme when
secreted, as most extracellular fluids have concentrations of sugar-nucleotide donors
that are far below the Km's of the enzymes. as for lectin-like activity, Barry Shur
sez that cell-surface located galactosyltransferase functions as a lectin/cell
adhesion molecule during sperm-egg interactions.
i think the main purpose of these secreted transferases is to facilitate their
purification :) !
just my $0.02
