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 asymm etrically reincorporated into egg phosphatidylcholine vesicles. Proteo lytic treatments and immunotitration studies demonstrated that this en zyme was integrated in native and artificial membrane vesicles with a similar topology. The uptake of free glucose and glucose produced by m altose hydrolysis was studied using 1) proteoliposomes containing inte grated neutral alpha-D-glucosidase, in combination with other membrane proteins, and 2) proteoliposomes containing only the other membrane p roteins but incubated in a medium containing neutral alpha-D-glucosida se in its hydrophilic form. No modification was observed in the uptake of free D-glucose or D-glucose produced by maltose hydrolysis, regard less of enzyme localization. In contrast to previous findings on the h ydrolase-related transport concept, these results rule out any partici pation of neutral alpha-D-glucosidase in the transport of free glucose or glucose produced by maltose hydrolysis. Hydrolytic activity and tr ansmembrane transport appear to be two independent and sequential step s.