The Enzyme Database

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EC 2.4.1.357     
Accepted name: phlorizin synthase
Reaction: UDP-α-D-glucose + phloretin = UDP + phlorizin
For diagram of phloretin biosynthesis, click here
Glossary: phloretin = 3-(4-hydroxyphenyl)-1-(2,4,6-trihydroxyphenyl)propan-1-one
phlorizin = 3-(4-hydroxyphenyl)-1-[2-(β-D-glucopyranosyloxy)-4,6-dihydroxyphenyl]propan-1-one
Other name(s): MdPGT1: P2’GT
Systematic name: UDP-α-D-glucose:phloretin 2′-O-D-glucosyltransferase
Comments: Isolated from Malus X domestica (apple). Phlorizin inhibits sodium-linked glucose transporters. It gives the characteristic flavour of apples and cider.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc
References:
1.  Jugdé, H., Nguy, D., Moller, I., Cooney, J.M. and Atkinson, R.G. Isolation and characterization of a novel glycosyltransferase that converts phloretin to phlorizin, a potent antioxidant in apple. FEBS J. 275 (2008) 3804–3814. [DOI] [PMID: 18573104]
2.  Yahyaa, M., Davidovich-Rikanati, R., Eyal, Y., Sheachter, A., Marzouk, S., Lewinsohn, E. and Ibdah, M. Identification and characterization of UDP-glucose:Phloretin 4′-O-glycosyltransferase from Malus x domestica Borkh. Phytochemistry 130 (2016) 47–55. [DOI] [PMID: 27316677]
[EC 2.4.1.357 created 2018]
 
 
EC 3.2.1.62     
Accepted name: glycosylceramidase
Reaction: (1) a β-D-glucosyl-N-acylsphingosine + H2O = a ceramide + β-D-glucose
(2) a β-D-galactosyl-N-acylsphingosine + H2O = a ceramide + β-D-galactose
(3) a flavonoid-O-β-D-glucoside + H2O = a flavonoid + β-D-glucose
For diagram of phloretin biosynthesis, click here and for diagram of glycolipid biosynthesis, click here
Glossary: a ceramide = an N-acylsphingosine
Other name(s): phlorizin hydrolase; phloretin-glucosidase; glycosyl ceramide glycosylhydrolase; cerebrosidase; phloridzin β-glucosidase; lactase-phlorizin hydrolase; phloridzin glucosidase; LPH (gene name); LCT (gene name); glycosyl-N-acylsphingosine glycohydrolase
Systematic name: β-D-glucosyl-N-acylsphingosine glycohydrolase (configuration-retaining)
Comments: The enzyme, found in the intestinal mucosa, hydrolyses β-D-glucosyl and β-D-galactosyl residues from a very broad range of substrates using a retaining mechanism. Characterized substrates include glucosyl- and galactosyl-ceramides [3], O3-, O4′ and O7-glucosylated flavonoids [6], and the 2′-O-glucosylated dihydrochalcone phlorizin [1]. The enzyme includes two glycosyl hydrolase domains, both belonging to the GH1 family. While one domain is responsible for the activity described here, the other catalyses the reaction of EC 3.2.1.108, lactase [4,5]. cf. EC 3.2.1.45, glucosylceramidase and EC 3.2.1.46, galactosylceramidase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 9033-10-7
References:
1.  Malathi, P. and Crane, R.K. Phlorizin hydrolase: a β-glucosidase of hamster intestinal brush border membrane. Biochim. Biophys. Acta 173 (1969) 245–256. [DOI] [PMID: 5774775]
2.  Lorenz-Meyer, H., Blum, A.L., Haemmerli, H.P. and Semenza, G. A second enzyme defect in acquired lactase deficiency: lack of small-intestinal phlorizin-hydrolase. Eur. J. Clin. Invest. 2 (1972) 326–331. [DOI] [PMID: 5082068]
3.  Leese, H.J. and Semenza, G. On the identity between the small intestinal enzymes phlorizin hydrolase and glycosylceramidase. J. Biol. Chem. 248 (1973) 8170–8173. [DOI] [PMID: 4752949]
4.  Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. and Semenza, G. Intestinal lactase-phlorizin hydrolase (LPH): the two catalytic sites; the role of the pancreas in pro-LPH maturation. FEBS Lett. 435 (1998) 225–228. [DOI] [PMID: 9762914]
5.  Arribas, J.C., Herrero, A.G., Martin-Lomas, M., Canada, F.J., He, S. and Withers, S.G. Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolase. Eur. J. Biochem. 267 (2000) 6996–7005. [DOI] [PMID: 11106409]
6.  Nemeth, K., Plumb, G.W., Berrin, J.G., Juge, N., Jacob, R., Naim, H.Y., Williamson, G., Swallow, D.M. and Kroon, P.A. Deglycosylation by small intestinal epithelial cell β-glucosidases is a critical step in the absorption and metabolism of dietary flavonoid glycosides in humans. Eur J Nutr 42 (2003) 29–42. [DOI] [PMID: 12594539]
[EC 3.2.1.62 created 1972, modified 1976, modified 2022]
 
 
EC 3.2.1.108     
Accepted name: lactase
Reaction: lactose + H2O = β-D-galactose + D-glucose
Glossary: lactose = β-D-galactopyranosyl-(1→4)-α-D-glucopyranose
Other name(s): lactase-phlorizin hydrolase; LPH (gene name); LCT (gene name)
Systematic name: lactose galactohydrolase (configuration-retaining)
Comments: The enzyme from intestinal mucosa contains two glycosyl hydrolase domains, both of which belong to glycosyl hydrolase family 1 (GH1). While the first domain catalyses the activity described here, the second domain catalyses the reaction of EC 3.2.1.62 glycosylceramidase. cf. EC 3.2.1.33 amylo-α-1,6-glucosidase.
Links to other databases: BRENDA, EXPASY, KEGG, MetaCyc, CAS registry number: 9031-11-2
References:
1.  Asp, N.G., Dahlqvist, A. and Koldovský, O. Human small-intestinal β-galactosidases. Separation and characterization of one lactase and one hetero β-galactosidase. Biochem. J. 114 (1969) 351–359. [PMID: 5822067]
2.  Schlegel-Haueter, S., Hore, P., Kerry, K.R. and Semenza, G. The preparation of lactase and glucoamylase of rat small intestine. Biochim. Biophys. Acta 258 (1972) 506–519. [DOI] [PMID: 5010299]
3.  Lorenz-Meyer, H., Blum, A.L., Haemmerli, H.P. and Semenza, G. A second enzyme defect in acquired lactase deficiency: lack of small-intestinal phlorizin-hydrolase. Eur. J. Clin. Invest. 2 (1972) 326–331. [DOI] [PMID: 5082068]
4.  Ramaswamay, S. and Radhakrishnan, A.N. Lactase-phlorizin hydrolase complex from monkey small intestine. Purification, properties and evidence for two catalytic sites. Biochim. Biophys. Acta 403 (1975) 446–455. [DOI] [PMID: 810166]
5.  Skovbjerg, H., Sjöström, H. and Norén, O. Purification and characterization of amphiphilic lactase-phlorizin hydrolase from human small-intestine. Eur. J. Biochem. 114 (1981) 653–661. [DOI] [PMID: 6786877]
6.  Skovbjerg, H., Norén, O., Sjöström, H., Danielsen, E.M. and Enevoldsen, B.S. Further characterization of intestinal lactase/phlorizin hydrolase. Biochim. Biophys. Acta 707 (1982) 89–97. [DOI] [PMID: 6814489]
7.  Zecca, L., Mesonero, J.E., Stutz, A., Poiree, J.C., Giudicelli, J., Cursio, R., Gloor, S.M. and Semenza, G. Intestinal lactase-phlorizin hydrolase (LPH): the two catalytic sites; the role of the pancreas in pro-LPH maturation. FEBS Lett. 435 (1998) 225–228. [DOI] [PMID: 9762914]
8.  Arribas, J.C., Herrero, A.G., Martin-Lomas, M., Canada, F.J., He, S. and Withers, S.G. Differential mechanism-based labeling and unequivocal activity assignment of the two active sites of intestinal lactase/phlorizin hydrolase. Eur. J. Biochem. 267 (2000) 6996–7005. [DOI] [PMID: 11106409]
[EC 3.2.1.108 created 1984, modified 2022]
 
 


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