Cytosolic /?-glucosidase

The only other examples of bromoconduritol inhibition reported so far are a cytosolic jff-D-glucosidase from calf liver and the lysosomal ff-D-glu-cosidase from calf spleen. In spite of the 6500-fold difference in their reactivity with conduritol B epoxide (see Table XI), both enzymes are rapidly inactivated by bromoconduritol F, with kj(max)/Kj 10 M min for the cytosolic enzyme and lq(max)/Ki 3.2 10 for the crude and 3.9 10 M min for the purified lysosomal enzyme. It should be noted that purification of the lysosomal jS-D-glucosidase had effects on the reactivity with bromoconduritol F similar to those it had on the reactivity with conduritol B epoxide (see Table XI). 

Potential enzymes involved in anthocyanin metabolism — The lactase phlorizin hydrolase (LPH EC 3.2.1.108) present only in the small intestine on the outside of the brush border membrane and the cytosolic P-glucosidase (CBG EC 3.2.1.1) found in many tissues, particularly in liver, can catalyze the deglycosylation (or hydrolysis) of polyphenols. LPH may play a major role in polyphenol metabolism... 

G. Legler and E. Bieberich, Isolation of cytosolic P-glucosidase from calf liver and characterization of its active site with alkyl glucosides and basic glycosyl derivatives, Arch. Biochem. Biophys., 260 (1988) 427 136. 

Figure 2.1 Key step Luminal deglycosylation by LPH. For glycosylated flavonolds, this step determines whether the flavonold Is absorbed In the small Intestine. Degly-cosylatlon Is catalyzed by the brush border hydrolase, lactase phlorizin hydrolase. The alternative of transport by a sugar transporter followed by hydrolysis by cytosolic p-glucosidase Is a minor pathway for some flavonolds.

Figure 21.23. Glycogen-Engorged Lysosome. This electron micrograph shows skeletal muscle from an infant with type II glycogen-storage disease (Pompe disease). The lysosomes are filled with glycogen because of a deficiency in a-1,4-glucosidase, a hydrolytic enzyme confined to lysosomes. The amount of glycogen in the cytosol is normal. [From H.-G. Hers and F. Van Hoof, Eds. Lysosomes and Storage Diseases (Academic Press, 1973), p. 205.]...

Cytosol lactate dehydrogenase leucine aminopeptidase p-glucosidase fructose-1,6 biphosphatase (proximal tubule) pyruvate kinase (distal tubule)... 

The fungus Papulaspora thermophila has been shown to degrade filter paper and soluble carboxymethylcellulose. Synthesis of the cellulolytic enzymes could be induced by cellulosic material added to the growth medium. A cytosolic P-D-glucosidase from Pseudomonas fluorescens possesses some exo-cellulase activity. " " ... 

Fig. 79.5 Hypothetic pathways of anthocyanin absorption, distribution, metabolism, and excretion based on current information (CGB-cytosolic beta-glucosidase SULT-sulfotransferase UDP-GT-glucuronosyltransferase COMT-catechoi-O-methyl transferase SGLT-sodium-dependent glucose cotransporters LPH-lactase-phlorizin hydrolase)...

Table 3 shows the substrate specificity of cytosolic p-glucosidase and LPH. It should be noted that the flavonols quercetin-3-glucoside and quercetin-4 -glucoside were substrates for the lactase domain of LPH and not the phlorizin hydrolase domain, as may have been expected, given that phlorizin has a... 

Lactase phlorizin hydrolase s Cytosolic p-glucosidase° Substrates for human small intestine extract Absorption in small intestine... 

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