CHARACTERISTICS OF D‐GLUCOSAMINE UPTAKE BY RAT BRAIN SYNAPTOSOMES

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Abstract
Abstract— The uptake of D‐glucosamine by rat brain synaptosomes is studied as a function of time, temperature and synaptosomal protein and substrate concentrations. The rate of D‐glucosamine uptake, after correcting for simple diffusion, obeys Michaelis‐Menten kinetics. The apparent kinetic constants for the uptake process are Km= 2.5 0.8 mm, Vmax= 3.7 ± 1.2 nmol/mg protein/min. D‐Glucose, D‐mannose, 2‐deoxy‐D‐glucose and 3‐0‐methyl‐o‐glucose are potent inhibitors of D‐glucosamine uptake. 2‐Deoxy‐D‐glucose and D‐glucosamine inhibit the uptake of one another in a simple competitive manner, indicating their sharing of a common transport system. Cytochalasin B, phloretin and phloridzin are powerful competitive inhibitors of D‐glucosamine uptake with apparent inhibitor constants (K1) of 7.0 × 10‐5, 2.3 × 10‐3 and 0.4 mM, respectively. The uptake is unaffected by Na+, Li+ and Mg2+, partially inhibited by NH4+, Mn2+ and Ca2+, and slightly stimulated by PO4‐ions. D‐Glucosamine uptake is also sensitive to inhibition by several sulfhydryl reagents, thus implying the involvement of sulfhydryl groups in the transport process. The apparent affinity constants for synaptosomal transport for both D‐glucosamine and 2‐deoxy‐D‐glucose are about 4 times greater in 7‐day‐old than in the adult rat brains.