Neutral maltase of human granulocytes: localization on the extracytoplasmic side of the plasma membrane and some properties.
Neutral maltase is an alpha-glucosidase (alpha-D-glucoside glucohydrolase, EC 3.2.1.20) which is present in human 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 human 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 maltose and nigerose but not other glucosides disaccharides and oligosaccharides. The Km for maltose is (+/- SD) 0.78 (+/- 0.06) mM, that for nigerose 21.05 (+/- 1.43) mM. The Vmax for nigerose is 0.83-fold that for maltose. Tris, maltotriose, maltotetraose, and maltopentaose were inhibitors of granulocyte neutral maltase.
Stio
M
M
Dipartimento di Scienze Biochimiche, Universitá di Firenze, Italy.
Vanni
P
P
Ferrini
P R
PR
Giachetti
E
E
Bosi
A
A
Pinzauti
G
G
D001799:Blood Sedimentation; D002462:Cell Membrane / Q000201:enzymology; D002469:Cell Separation; D002499:Centrifugation, Density Gradient; D002784:Cholesterol / Q000032:analysis; D006098:Granulocytes / Q000201:enzymology*; D006461:Hemolysis; D006801:Humans; D007700:Kinetics; D009504:Neutrophils / Q000201:enzymology; D010447:Peptide Hydrolases / Q000378:metabolism; D012995:Solubility; D013347:Subcellular Fractions; D000520:alpha-Glucosidases / Q000097:blood*
D002784:Cholesterol; D000520:alpha-Glucosidases; D010447:Peptide Hydrolases