Mammalian lactase-phlorizin hydrolase (LPH) (EC 18.104.22.168 / EC 22.214.171.124).
LPH, an integral membrane glycoprotein, is the enzyme that splits lactose
in the small intestine. LPH is a large protein of about 1900 residues which
contains four tandem repeats of a domain of about 450 residues which is
evolutionary related to the above glycosyl hydrolases.
One of the conserved regions in these enzymes is centered on a conserved
glutamic acid residue which has been shown , in the β-glucosidase from
Agrobacterium, to be directly involved in glycosidic bond cleavage by acting
as a nucleophile. We have used this region as a signature pattern. As a second
signature pattern we selected a conserved region, found in the N-terminal
extremity of these enzymes, this region also contains a glutamic acid residue.
This pattern will pick up the last two domains of LPH; the first two
domains, which are removed from the LPH precursor by proteolytic processing,
have lost the active site glutamate and may therefore be inactive .
El Hassouni M., Henrissat B., Chippaux M., Barras F.
J. Bacteriol. 174:765-777(1992).
Withers S.G., Warren R.A.J., Street I.P., Rupitz K., Kempton J.B., Aebersold R.
J. Am. Chem. Soc. 112:5887-5889(1990).
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