ß-galactosidase

DEFINITION:

Any of a group of enzymes of the hydrolase class that catalyze the cleavage of terminal, ß-linked, nonreducing galactose residues from a variety of substrates, including ganglioside GM₁, lactosylceramides, lactose, and various glycoproteins and oligosaccharides.

glycosylceramidase

DEFINITION:

An enzyme [EC 3.2.1.62] of the hydrolase class that catalyzes the cleavage of ß-linked sugar residue from ß-glycosides with large hydrophobic aglycons, such as galactosyl- and glycosylceramides and phlorizin. Such enzyme activity occurs as part of the ß-glycosidase complex, along with lactase, in the intestinal brush border membrane, where it is frequently referred to as phlorhizin hydrolase . In this context, it is sometimes described as a composite of glucosylceramidase [EC 3.2.1.45] and galactosylceramidase [EC 3.2.1.46] activities and denoted glycosylceramidase [EC 3.2.1.45-6].

phlorizin hydrolase

DEFINITION:

See phlorhizin hydrolase.

ß-glycosidase complex

DEFINITION:

The enzyme complex comprising lactase and glycosylceramidase (phlorhizin hydrolase) activities, occurring in the brush border membrane of the intestinal mucosa and hydrolyzing lactose as well as cellobiose and cellotriose; it is a single polypeptide, processed from a larger precursor, with two catalytic sites for the two enzyme activities.

enzyme

DEFINITION:

Any of numerous proteins that are produced by living cells and catalyze specific biochemical reactions at body temperatures.

catalyzes

DEFINITION:

Initiates a chemical reaction and enables it to proceed under different conditions (as at a lower temperature) than otherwise possible.

hydrolytic

DEFINITION:

Pertaining to, characterized by, or promoting hydrolysis.

cleavage

DEFINITION:

1. The act of cleaving or splitting.

2. The state of being cleft.

3. Biol. - The total or partial division of the egg into smaller cells or blastomeres.

4. The mitotic segmentation of the zygote, the size of the structure remaining unchanged, as the cleavage cells, or blastomeres, become smaller and smaller with each division.

5. Chem. - The breaking down of a molecule or compound into simpler structures.

lactose

DEFINITION:

1. A reducing disaccharide occurring as the D-isomer, in both a- and ß-configurations, as a major constituent of mammalian milk; on hydrolysis by acids or intestinal lactase, it forms one residue each of galactose and glucose.

2. An official preparation of lactose, usually a-D-lactose; used as a tablet and capsule diluent, a powder bulking agent, in infant feeding formulas, and as a nutritional supplement.

galactose

DEFINITION:

An aldohexose epimeric with glucose at the 4 carbon but less soluble and less sweet, occurring naturally in both D- and L- forms (the latter in plants); it is a component of lactose and other oligosaccharides, cerebrosides and gangliosides, and various glycolipids and glycoproteins.

glucose

DEFINITION:

1. A sugar C₆H₁₂O₆ known in dextrorotatory, levorotatory, and racemic forms; esp.: the sweet colorless soluble dextrorotatory form that occurs widely in nature and is the usual form in which carbohydrate is assimilated by animals.

2. A light-colored syrup made from cornstarch.

enzyme

DEFINITION:

Any of numerous proteins that are produced by living cells and catalyze specific biochemical reactions at body temperatures.

lactase deficiency

DEFINITION:

The most common disaccharidase deficiency, reduced or absent lactase activity in the intestinal mucosa, usually due to an inherited defect in the enzyme but sometimes secondary to disorders involving the small intestinal mucosa. The hereditary adult form, an autosomal recessive trait, is the normal state in most populations other than white Northern Europeans and may be characterized by abdominal pain, flatulence, and diarrhea after ingestion of milk ( lactose intolerance ); the rare hereditary congenital form, an autosomal recessive trait, is characterized by diarrhea, vomiting, and failure to thrive ( congenital lactose intolerance ).

lactose intolerance

DEFINITION:

A disaccharide intolerance specific for lactose, usually due to an inherited deficiency of lactase activity in the intestinal mucosa.