Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.3.5 (5'-nucleotidase)
 3,167 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Membrane vesicles were prepared from CHO-K1 and alanine-resistant transport mutants, alar4 and alar4-H3.9. Alar4 is a constitutive mutant of the A system, and alar4-H3.9, derived from alar4, may be the result of amplification of a gene coding for an A-system transporter. Under conditions in which the same membrane potential (interior negative) and Na+ gradient were employed, the mutant vesicles show increases in the A system over that of the parental CHO-K1 cell line, paralleling, but not equivalent to, that found in whole cells. L-system and 5'-nucleotidase activities of these vesicles were similar, indicating that the increased A-system activity of the mutant vesicles is not due to the differential enrichment of the A system in these vesicles. The membrane potential was produced by a K+ diffusion gradient (internal greater than external) in the presence of valinomycin or by the addition of a Na+ salt of a highly permeant anion such as SCN-. Monensin was employed to study the effect of the Na+ gradient on transport and membrane potential. The latter was determined by measuring the uptake of tetraphenylphosphonium ion. A negative membrane potential determines the concentrative ability and the initial velocity of the A system in these vesicles. The concentration of external Na+ has a stimulatory effect on the initial velocity of this system. However, the Na+ gradient (external greater than internal) has no effect on the initial velocity or the membrane potential when the potential is set by valinomycin and high internal K+. Little if any ASC system could be detected in vesicles from CHO-K1.
 ...
PMID:Amino acid transport in membrane vesicles from CHO-K1 and alanine-resistant transport mutants. 360 29

To characterize the placental amino acid transport systems, L-alanine and L-leucine uptakes were studied using microvillous brush border membrane vesicles prepared from human placenta. The specific activities of alkaline phosphatase and 5'-nucleotidase in the membrane preparation were enriched 9-11 times as high as those in the homogenate. Intravesicular water (IVW) volume determined with 3-O-methyl-D-glucose was 0.59 microliters/mg protein. The saturation kinetics of L-leucine uptake by the vesicles equilibrated with Na+ gave a single set of Km (4.2mM) and Vmax (1.16 mumol/ml IVW/30s). These parameters were clearly different from those for L-alanine uptake reported previously (Asai et al.: Biochem. Int., 4:377, 1982). In the presence of an inward Na+-gradient L-leucine uptake was stimulated about 2 times, but transient accumulation was not observed differing from L-alanine uptake. Discrimination of the neutral amino acid transport systems in the presence of an inward 100mM Na+-gradient revealed that the relative contributions of A, ASC and L systems, and simple diffusion were 55, 20, 15 and 10% for L-alanine, and 45, 0, 15 and 40% for L-leucine, respectively. The results indicate that the neutral amino acid transport systems in the human placental microvillous membranes are clearly different between L-alanine and L-leucine.
 ...
PMID:[Studies on the amino acid transport systems in the human placenta--L-alanine and L-leucine uptake by microvillous brush border membrane vesicles]. 629 24

Insufficient glutamine for the lungs during sepsis may contribute to an impairment in lung function. Lung glutamine metabolism is supported by both blood glutamine uptake and de novo biosynthesis using circulating glutamate as a precursor. Information regarding the specific plasma membrane carriers involved in this uptake is lacking. Furthermore, the effect of sepsis on amino acid transport in whole lung has not been studied. We isolated lung plasma membrane vesicles (LPMVs) from control and LPS-treated rats and assayed glutamine and glutamate transport activity in LPMVs. Vesicle purity and functionality were confirmed by time-dependent concentrative amino acid uptake in the presence of Na+, impoverishment of microsomal enzymes, and a 25-fold enrichment in the plasma membrane marker 5'-nucleotidase. Eighty percent of glutamine uptake in lung vesicles was mediated via the high affinity Na(+)-dependent carrier System ASC (Vmax = 80 +/- 10 pmole/mg protein/15 sec; Km = 224 +/- 30 microM) while 19% occurred via the Na(+)-independent System ASC (Vmax = 11 +/- 2 pmole/mg/15 sec; Km = 141 +/- 23 microM). Ninety percent of glutamate transport was mediated by the Na(+)-independent System XAG-. Treatment of rats with LPS resulted in a decrease in both glutamine and glutamate transport in LPMVs. LPMVs offer a novel method for characterizing lung amino acid transport and studying the effects of catabolic states on this activity. The effects of endotoxin on System ASC and XAG- activity may contribute to reduced lung glutamine availability during septic states which may impair cellular metabolism and function.
 ...
PMID:Characterization of glutamine and glutamate transport in rat lung plasma membrane vesicles. 922 17