Sucrose a-D-Glucohydrolases

Studies on the enzyme complex oligo-l,6-D-glucosidase-sucrose a-D-glucohydro-lase ( sucrase-isomaltase ) of the AB intestinal brush border membrane have shown that a hydrophobic section of the oligo-l,6-D-glucosidase is responsible for binding of the complex to the membrane (see p. 522).  

01igo-l,6-D-glucosidase-sucrose a-D-glucohydrolase ( sucrase-isomaltase ) is an intestinal membrane enzyme consisting of two active moieties each with its hydrolytic site available for nutrient digestion at the luminal-cell interface. 

At least 90% of the hydrolytic activity can be localized to the brush border membrane and the remainder in the cytoplasm has been considered to originate from brush border contamination (see p. 451). 

The concurrent action of sucrose a-D-glucohydrolase and oligo-l,6-D-gluco-sidase active sites of the hybrid oligo-l,6-D-glucosidase-sucrose a-D-glucohydrolase ( sucrose-isomaltase ) from rat intestine on an a-limit dextrin was studied by use of 6 -maltotriosylmaltotriose isolated from the products of controlled action of pullulanase on pullulan (see p. 522).  

Some of the amino-acid sequences surrounding the essential carboxylic acid group in the active sites of the sucrose a-D-glucohydrolase oligo-l,6-D-glucosidase (sucrase-isomaltase) complex of rabbit small intestines have been determined by selective labelling with [ H]conduritol-B epoxide.  

The rate of synthesis of sucrose a-D-glucohydrolase is decreased in the small intestines of thyroidectomized and adrenalectomized rats.  

Electrophoresis on polyacrylamide gels of materials from brush-border membranes of siblings with a deficiency of sucrose a-D-glucohydrolase-oligo-1,6-D-glucosidase ( sucrase - isomaltase ) did not reveal the normal protein band associated with the complex.  

Treatment of closed, right-side-out vesicles of porcine, rabbit, and rat jejunum brush borders with papain and Triton X-100 released a sucrose a-D-glucohydrolase that had been bound to the membrane without grossly aifecting the lipid bilayers limiting the vesicles. It was concluded that intestinal sucrose a-D-glucohydrolase is attached to the outside of the membrane. 

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The jS-D-fructofuranosidase (see also sucrose a-D-glucohydrolases) released from the vesicles of human intestinal brush-border membranes by various enzymes, particularly pancreatic proteases, has been studied. The results were discussed in terms of the location and chemical binding of the jS-o-fructofuranosidase. 

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