Uptake of glycosylated ?-galactosidase into human brain synaptosomes: Occurrence of two different systems for specific glycosides.
Uptake of glycoproteins into brain nerve terminals was studied, using glycosylated ?-galactosidase and human brain synaptosomes. A series of p-aminophenyl ?- or ?-glycosides were covalently bound to ?-galactosidase purified from Aspergillus oryzae and uptake of the enzyme into human brain synaptosomes was measured. ?-Galactosidase coupled with ?-d-mannoside (?-d-Man ?-gal) was the best to be taken up among glycoconjugates tested. The uptake was dependent on the amount of ?-d-Man ?-gal, the incubation temperature and the incubation time. Kinetic studies showed that the uptake was a saturable and receptor-mediated process, which followed Michaelis-Menten kinetics. The specificity of the uptake was confirmed by competition of the uptake of ?-d-Man ?-gal by ?-methyl mannoside. The uptake was dependent on Ca(2+) and that of ?-galactosidase coupled with ?-l-fucoside (?-l-Fuc ?-gal) was saturated by Ca(2+) at lower concentrations than that Of ?-d-Man ?-gal.Occurrence of two different uptake systems was also suggested by kinetic study; a low-affinity and high-capacity system for ?-d-mannoside and a high-affinity and low-capacity system for ?-l-fucoside. The former system may be mediated by a process coupled with a Ca(2+)/calmodulin-dependent protein kinase, but the later may not be dependent on the protein kinase.
Naoi
M
M
Department of Biochemistry, Nagoya University School of Medicine, Nagoya, Japan.
Iwashita
T
T
Nagatsu
T
T