0-Glucosidase, cofactors

Assay. Acid p-glucosidase hydrolyzes both water-soluble and lipid substrates. The activity, and hence the activation of this enzyme by cofactors, can therefore be determined with either kind of substrate. Due to the rapidity and convenience of assays with fluorogenic substrates, most workers prefer to use the commercially available 4-methylumbelli-feryl-p-D-glucoside. In some cases it may, however, be desirable, or even necessary, to confirm the results with the natural substrate, glucosylceramide. Both types of assays will therefore be described here. 

The interaction between acid p-glucosidase and activating protein cofactors depends on the presence of acidic lipids (Ho and Light, 1973), so a certain amount of such lipids has to be added to the assay system. (The partially purified enzyme preparations used contain frequently some lipids, including acidic ones.) On the other hand, higher concentrations of acidic lipids may stimulate the enzyme to almost maximal activity (Berent and Radin, 1981a) and may render protein cofactors obsolete. 

Since the initial report by Ho and O Brien (1971) that lysosomal P-glucosidase activity toward water-soluble substrates as well as glucosylceramide (Ho et al., 1973) is greatly stimulated by small nonenzy-mic protein cofactors that are particularly abundant in Gaucher spleen, such factors have been purified by several groups from human spleen (Ho and O Brien, 1971 Peters et al., 1977a, b Chiao et al., 1978 Iyer et... 

Figure Simplified scheme for the biosynthesis of the antiar- > rhythmic agent ajmaline. Only the key steps are shown in the scheme. The cofactors given on the left side participate in individual enzymatic reactions. The following enzymes were identified in the 15-step sequence leading to the final product ajmaline 1 strictosidine synthase 2 strictosidine glucosidase ...

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