Renal neutral alpha-D-glucosidase has no role in transport of D-glucose derived from maltose hydrolysis.
To reinvestigate the "hydrolase-related transport" concept, neutral alpha-D-glucosidase, a membrane-bound disaccharidase of renal proximal tubule, was first purified from brush-border membranes and then asymmetrically reincorporated into egg phosphatidylcholine vesicles. Proteolytic treatments and immunotitration studies demonstrated that this enzyme was integrated in native and artificial membrane vesicles with a similar topology. The uptake of free glucose and glucose produced by maltose hydrolysis was studied using 1) proteoliposomes containing integrated neutral alpha-D-glucosidase, in combination with other membrane proteins, and 2) proteoliposomes containing only the other membrane proteins but incubated in a medium containing neutral alpha-D-glucosidase in its hydrophilic form. No modification was observed in the uptake of free D-glucose or D-glucose produced by maltose hydrolysis, regardless of enzyme localization. In contrast to previous findings on the hydrolase-related transport concept, these results rule out any participation of neutral alpha-D-glucosidase in the transport of free glucose or glucose produced by maltose hydrolysis. Hydrolytic activity and transmembrane transport appear to be two independent and sequential steps.
Giudicelli
J
J
Laboratoire de Biochimie, Faculté de Médecine, Nice, France.
Delque-Bayer
P
P
Sudaka
P
P
Poiree
J C
JC
D000818:Animals; D001692:Biological Transport / Q000502:physiology; D005947:Glucose / Q000378:metabolism*; D006736:Horses; D006868:Hydrolysis; D007668:Kidney / Q000201:enzymology*; D007672:Kidney Cortex / Q000378:metabolism; D008081:Liposomes / Q000378:metabolism; D008320:Maltose / Q000378:metabolism*; D008871:Microvilli / Q000378:metabolism; D011510:Proteolipids / Q000378:metabolism; D000520:alpha-Glucosidases / Q000502:physiology*
D008081:Liposomes; D011510:Proteolipids; C020485:proteoliposomes; D008320:Maltose; D000520:alpha-Glucosidases; D005947:Glucose