Intestinal β-galactosidases

Abstract

ABSTRA CT Previous studies based on work in the rat and preliminary experiments with human intestine have suggested that two 8l-galactosidases are present in small intestine, and it is believed that only one of these enzymes is a lactase important for the digestion of dietary lactose. The high prevalence of intestinal lactase deficiency in man prompted more complete study of these enzymes.Human intestinal 8-galactosidases were studied by gel filtration on Sephadex G-200 and Biogel P-300 as well as by density gradient ultracentrifugation. Gel filtration produced partial separation into three peaks of enzyme activity, but much activity against synthetic substrates was lost. Only the trailing peak with specificity for synthetic 8-galactosides was completely separated from the other enzymes. Thus gel filtration was not a suitable preparative procedure for biochemical characterization.Density gradients separated the enzymes more completely, and they were designated according to their sedimentation rates and further characterized. Enzyme I has a molecular weight of 280,000, pH optimum of 6.0, and specificity for lactose of at least five times that for cellobiose or synthetic substrates. A second lactase, enzyme II, possesses slightly greater activity against lactose than for some synthetic substrates and is incapable of splitting cellobiose. Further, it has a lower pH optimum (4.5) and is present in two molecular species (molecular weights 156,000 and 660,000). Enzyme INTRODUCTIONThe lactose in milk is a principal source of calories for children, and this disaccharide is important food for adult nutrition in many areas of the world. However, man's ability to digest lactose is limited, presumably because intestinal mucosal lactase is normally less active than the other disaccharidases (1, 2). In fact lactose is split so slowly that the hydrolysis step is rate limiting for the over-all process of hydrolysis-transport in both normal adults (3) and children.' This is in contrast to the hydrolysis of other oligosaccharides by intestinal mucosal enzymes which occurs rapidly enough to provide for saturation of the intestinal monosaccharide transport mechanism (3, 4). Perhaps partly because of the relatively low lactase levels in normal man, frank deficiency of intestinal lactase, and consequent intolerance to lactose-containing foods has been found to be frequent in individuals from certain population groups (5, 6) as well as in healthy people who appear to retain this defect as a permanent residual of previous intestinal disease (7,8).

Blimp1 regulates the transition of neonatal to adult intestinal epithelium

“…Our current studies identified another disaccharidase with the potential to metabolize lactase as specific for the normal neonatal epithelium. We found that the enterocytes express β-galactosidase in the cytoplasmic vacuoles in this period3334. In contrast, after the suckling period, the brush border is better developed and contains sucrase isomaltase, a disaccharidase that can digest fructose and more complex carbohydrates.…”

“…In the list of downregulated genes, we identified β-galactosidase, an enzyme that we found is specifically expressed in the sucking period when it localizes to the cytoplasmic vacuoles (see below). This β-galactosidase expression during the suckling period is likely involved in the cytoplasmic processing of lactose 33 34 . The Illumina array did not contain any probe set for the lactase gene, the major brush border enzyme involved in lactose metabolism, but we were able to confirm its downregulation at the protein level (see below).…”

Isolation of a β-Galactosidase from Chicken Liver

“…The ß-galactosidase in intestinal mucosa plays a role in the digestion of disaccharides (3,4). Human liver ß-galactosidases (5) like those in mouse (6), feline (7) and dog liver (8) have been investigated with respect to the number of their multiple forms and their diverse Substrate specificities.…”

Hydrolysis of GM1-ganglioside by human liver β-galactosidase isoenzymes

“…Enzymic cleavage of naturally occurring fl-galactosidic linkages have been demonstrated in glycolipids (Gatt & Rapport, 1966;Gatt, 1967;Bowen & Radin, 1968;Okada & O'Brien, 1968;Dawson & Stein, 1970), glycoproteins and mucopolysaccharides (Mahadevan et al, 1969;MacBrinn et al, 1969). Differential specificity for lactose is well known among the isoenzymes in small intestine (Asp & Dahlqvist, 1968;Alpers, 1969;Gray & Santiago, 1969). As yet, no definitive studies on the specificity of the P-galactosidase isoenzymes for glycolipids have been performed (nor for glycoproteins or mucopolysaccharides).…”