Neutral maltase of XXXX granulocytes: localization on the extracytoplasmic side of the plasma membrane and some properties.

@entity1 @entity35562 @entity7969 @entity21840 @entity40145
Neutral maltase is an alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) which is present in @entity1 granulocytes and B-lymphocytes but not in T-lymphocytes. These cells have been reported to contain a renal-type neutral maltase which cross-reacts with an antiserum raised against kidney brush-border enzyme. No study has been performed to assess the subcellular localization of the enzyme. Molecular properties of leukocyte neutral maltase from any species are unknown. We report in this paper that neutral maltase is present on the extracytoplasmic side of @entity1 granulocyte plasma membrane. These results are supported by subcellular fractionation on Percoll gradient and by papain digestion of intact granulocytes. The enzyme is probably an integral membrane protein. The anchorage to the lipid bilayer may be similar to that of the stalked brush-border hydrolases. Some properties of granulocyte neutral maltase were also determined on a plasma membrane-enriched fraction. The enzyme cleaves @entity7969 and @entity40145 but not other glucosides disaccharides and oligosaccharides. The Km for @entity7969 is (+/- SD) 0.78 (+/- 0.06) mM, that for @entity40145 21.05 (+/- 1.43) mM. The Vmax for @entity40145 is 0.83-fold that for @entity7969 . Tris, @entity21840 , @entity35562 , and maltopentaose were inhibitors of granulocyte neutral maltase.
