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2015 ; 29
(6
): 2583-94
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Integration of computational modeling with membrane transport studies reveals new
insights into amino acid exchange transport mechanisms
#MMPMID25761365
Widdows KL
; Panitchob N
; Crocker IP
; Please CP
; Hanson MA
; Sibley CP
; Johnstone ED
; Sengers BG
; Lewis RM
; Glazier JD
FASEB J
2015[Jun]; 29
(6
): 2583-94
PMID25761365
show ga
Uptake of system L amino acid substrates into isolated placental plasma membrane
vesicles in the absence of opposing side amino acid (zero-trans uptake) is
incompatible with the concept of obligatory exchange, where influx of amino acid
is coupled to efflux. We therefore hypothesized that system L amino acid exchange
transporters are not fully obligatory and/or that amino acids are initially
present inside the vesicles. To address this, we combined computational modeling
with vesicle transport assays and transporter localization studies to investigate
the mechanisms mediating [(14)C]L-serine (a system L substrate) transport into
human placental microvillous plasma membrane (MVM) vesicles. The carrier model
provided a quantitative framework to test the 2 hypotheses that l-serine
transport occurs by either obligate exchange or nonobligate exchange coupled with
facilitated transport (mixed transport model). The computational model could only
account for experimental [(14)C]L-serine uptake data when the transporter was not
exclusively in exchange mode, best described by the mixed transport model. MVM
vesicle isolates contained endogenous amino acids allowing for potential
contribution to zero-trans uptake. Both L-type amino acid transporter (LAT)1 and
LAT2 subtypes of system L were distributed to MVM, with L-serine transport
attributed to LAT2. These findings suggest that exchange transporters do not
function exclusively as obligate exchangers.
|*Computer Simulation
[MESH]
|*Models, Biological
[MESH]
|Amino Acid Transport System y+/metabolism
[MESH]
|Amino Acids/*metabolism/pharmacokinetics
[MESH]
|Biological Transport
[MESH]
|Blotting, Western
[MESH]
|Carbon Radioisotopes
[MESH]
|Cell Membrane/*metabolism
[MESH]
|Female
[MESH]
|Fluorescent Antibody Technique
[MESH]
|Fusion Regulatory Protein 1, Light Chains/metabolism
[MESH]