EFFECTS OF TRUNCATION OF THE COOH-TERMINAL REGION OF A NA-INDEPENDENTNEUTRAL AND BASIC-AMINO-ACID TRANSPORTER ON AMINO-ACID-TRANSPORT IN XENOPUS OOCYTES()
K. Miyamoto et al., EFFECTS OF TRUNCATION OF THE COOH-TERMINAL REGION OF A NA-INDEPENDENTNEUTRAL AND BASIC-AMINO-ACID TRANSPORTER ON AMINO-ACID-TRANSPORT IN XENOPUS OOCYTES(), The Journal of biological chemistry, 271(28), 1996, pp. 16758-16763
To determine the role of a neutral and basic amino acid transporter (N
EAT) in amino acid transport, we microinjected several COOH-terminal d
eletion mutants of NEAT cRNA into Xenopus oocytes and measured transpo
rt activity for arginine, leucine, and cystine in the presence and abs
ence of sodium, Wild type NEAT significantly stimulated the uptake of
all three amino acids 10-20-fold compared with controls, On the other
hand, no mutant, except a Delta 511-685 mutant, stimulated the uptake
of these amino acids, The Delta 511-685 mutant significantly increased
the uptake of arginine. In the presence of sodium, the Delta 511-685
mutant also increased the uptake of leucine, The Delta 511-685 mutant
did not stimulate cystine uptake in the presence or absence of sodium,
The stimulation of arginine uptake by the Delta 511-685 mutant was in
hibited by a 100-fold excess of unlabeled leucine in the presence of s
odium, Inhibition of L-arginine uptake by L-homoserine was seen only i
n the presence of sodium, and an increase in the inhibition of L-argin
ine uptake by L-histidine was seen when the extracellular pH was decre
ased, Furthermore, an inward current in oocytes injected with the Delt
a 511-685 mutant was recorded electrophysiologically when basic amino
acids were applied, Homoserine was also taken up, but sodium was neces
sary for their transport, These properties of the Delta 511-685 mutant
correspond to those of the y(+) amino acid transporter, If NEAT is a
component of the b(0,+)-like amino acid transport system, it is unlike
ly that a mutant protein (Delta 511-685) is able to stimulate an endog
enous y(+)-like transport system, These results suggest that NEAT func
tions as a activator of the amino acid transport system in Xenopus ooc
ytes.