152
ERNEST SCHOFFENIELS
TABLE X
SPECIFICITY OF INTESTINAL SUGAR TRANSPORT: RESULTS OBTAINED WITH
GLUCOSE, NONMETABOLIZABLE ANALOGS OF GLUCOSE AND OTHER SUGARS (62)
Compounds actively transported
D-Glucose
4-O-Methyl-D-galactose
1,5-Anhydro-D-glucitol
D-Allose
2-C-Hydroxymethyl-D-glucose
6-Deoxy-D-glucose
D-Glucoheptulose
6-Deoxy-D-galactose
3-O-Methyl-D-glucose
6-Deoxy-6-fluoro-D-glucose
D-Galactose
7-Deoxy-D-glucoheptose
3-Deoxy-D-glucose
a-Methyl-D-glucoside
Compounds not actively transported
D-Mannoheptulose
3-O-Propyl-D-glucose
D-Mannose
3-O-Butyl-D-glucose
D-Talose
3-O-Hydroxyethyl-D-glucose
1,5-Anh ydr o-D-mannit ol
1,4-Anhydro-D-glucitol
2-Deoxy-D-glucose
Gold-thioglucose
2-Deoxy-D-galactose
D-Gulose
2-O-Methyl-D-glucose
6-Deoxy-6-i odo-D-galactose
D-Glucosamine
6-0-Methyl-D-glucose
iV-Acetyl-D-glucosamine
L-Galactose
2,4-Di-O-methyl-D-galactose
L-Glucose
D-Fructose
L-Sorbose
3-0-Methyl-D-fructose
6-Deoxy-L-galactose
3-0-Ethyl-D-glucose
6-Deoxy-L-mannose
d-Xylose
Mannitol
L-Xylose
Sorbitol
D-Ribose
Glycerol
L-Arabinose
D-Arabinose
by Ussing (73) differs from simple diffusion, in that it is carrier
dependent, produces no net flux, and is specific. Sugar uptake has most
of these characteristics. It occurs without accumulation, is stereospecific,
and is inhibited by glucose, presumably owing to competition for entry
sites (72). The observation that glucose inhibits transport of nonfermentable sugars suggests a competition for some membrane transport
sites.
In human or rabbit red cells, sugar transport seems also to involve
a carrier molecule, but without uphill transport. Thus this does not
appear to be an active transport mechanism. Glucose inhibits the exchange of galactose and maltose inhibits the transfer of glucose or
galactose in erythrocytes (74).
Specificity, competition between different sugars for the transport,