High-affinity uptake system for cysteine in crude synaptosomal fractions of rat cerebral cortex.
The in vitro uptake of [35S] cysteine was studied in crude synaptosomal preparation of the cerebral cortex of rat. The accumulation of cysteine was found to be temperature- and time-dependent. It was linear at least for four minutes at 37 C with characteristics of saturable kinetics. Uptake of cysteine was Na+- and K+-dependent. Increasing the Na+ ion concentration increased the accumulation of cysteine in synaptosomal preparations; unlike the Na+ ion, an increase was accumulated against concentration gradients by a saturable mechanism. Double reciprocal plot of the cysteine uptake suggests two types of affinity systems, with Km values for the high-affinity uptake of about 12.2 microM and for the low-affinity uptake of about 4 mM. The high-affinity uptake was also significantly inhibited by ouabain, a potent inhibitor of the Na+-K+-dependent ATPase, and other metabolic inhibitors. The results of the effects of cysteine analogues and uptake also suggested that it is a substrate-specific high-affinity uptake system for cysteine.
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D002540:Cerebral Cortex / Q000378:metabolism*; D003545:Cysteine / Q000378:metabolism*; D007700:Kinetics; D008297:Male; D011188:Potassium / Q000378:metabolism; D051381:Rats; D012964:Sodium / Q000378:metabolism; D013574:Synaptosomes / Q000378:metabolism*
D000596:Amino Acids; D012964:Sodium; D003545:Cysteine; D011188:Potassium