Abstract
The transport of [14C]glycyl-glycine (Gly-Gly) has been characterized in leaf discs from mature exporting leaves of broad bean (Vicia faba L.). In terms of glycine (Gly) equivalents, the rate of transport of Gly-Gly was similar to that of Gly uptake. Uptake of Gly-Gly was localized mainly in the mesophyll cells, with little accumulation in the veins. It was optimal at pH 6.0, sensitive to thiol reagents and metabolic inhibitors, and exhibited a single saturable phase with an apparent Michaelis constant of 16 mM. Gly-Gly did not inhibit the uptake of labeled Gly. Addition of Gly-Gly induced a concentration-dependent pH rise in the medium, showing that peptide uptake is mediated with proton co-transport. Gly-Gly also induced a concentration-dependent transmembrane depolarization of mesophyll cells with an apparent Michaelis constant of 15 mM. This depolarization was followed by a transient hyperpolarization. When present at a 10-fold excess, various peptides and tripeptides were able to inhibit Gly-Gly uptake with the following decreasing order of efficiency: Gly-Gly-Gly = leucine-Gly > Gly-tyrosine > Gly-glutamine = Gly-glutamic acid > Gly-phenylalanine > Gly-threonine > Gly-aspartic acid = Gly-asparagine = aspartic acid-Gly. Gly inhibited the uptake of Gly-Gly only slightly, whereas tetraGly and the tripeptide glutathione were not inhibitory. The dipeptides inhibiting Gly-Gly uptake also induced changes in the transmembrane potential difference of mesophyll cells and were able to affect in a complex way the response normally induced by Gly-Gly. Altogether, the data demonstrate the existence of a low-affinity, broad-specificity H+/peptide co-transporter at the plasma membrane of mesophyll cells. The physiological importance of this transporter for the exchange of nitrogenous compounds in mature leaves remains to be determined, as do the details of the electrophysiological events induced by the dipeptides.
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Claims 16
Claim · model-written summary
Gly-Gly transport rate was similar to Gly uptake in glycine equivalents.
- Taxon
- broad bean
Vicia fabat0 - Organ / stage
- leaft0
- Outcome
- rate of transport of Gly-Glye0
- Direction
- similare0
- Comparator
- Gly uptakee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the rate of transport of Gly-Gly was similar to that of Gly uptake”
t0“broad bean leaf”
Claim · model-written summary
Gly-Gly uptake occurred mainly in mesophyll cells, with little vein accumulation.
- Taxon
- broad beanVicia fabat0
- Organ / stage
- mesophyll cellse0
- Outcome
- Uptake of Gly-Glye0
- Qualifier
- little accumulation in the veinse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Uptake of Gly-Gly was localized mainly in the mesophyll cells, with little accumulation in the veins”
t0“broad bean”
Claim · model-written summary
Gly-Gly uptake was optimal at pH 6.0.
- Taxon
- broad beanVicia fabat0
- Outcome
- optimale0
- Value
- pH 6.0e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“It was optimal at pH 6.0”
t0“broad bean”
Claim · model-written summary
Gly-Gly uptake was sensitive to thiol reagents and metabolic inhibitors.
- Taxon
- broad beanVicia fabat0
- Treatment
- thiol reagents and metabolic inhibitorse0
- Outcome
- sensitivee0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sensitive to thiol reagents and metabolic inhibitors”
t0“broad bean”
Claim · model-written summary
Gly-Gly uptake had one saturable phase with an apparent Michaelis constant of 16 mM.
- Taxon
- broad beanVicia fabat0
- Outcome
- apparent Michaelis constante0
- Value
- 16 mMe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“exhibited a single saturable phase with an apparent Michaelis constant of 16 mM”
t0“broad bean”
Claim · model-written summary
Gly-Gly did not inhibit labeled Gly uptake.
- Taxon
- broad beanVicia fabat0
- Treatment
- Gly-Glye0
- Outcome
- uptake of labeled Glye0
- Direction
- did not inhibite0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gly-Gly did not inhibit the uptake of labeled Gly”
t0“broad bean”
Claim · model-written summary
Gly-Gly caused a concentration-dependent rise in medium pH.
- Taxon
- broad beanVicia fabat0
- Treatment
- Gly-Glye0
- Outcome
- pH rise in the mediume0
- Direction
- risee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Addition of Gly-Gly induced a concentration-dependent pH rise in the medium”
t0“broad bean”
Claim · model-written summary
Gly-Gly induced concentration-dependent mesophyll depolarization with an apparent Michaelis constant of 15 mM.
- Taxon
- broad beanVicia fabat0
- Treatment
- Gly-Glye0
- Outcome
- transmembrane depolarization of mesophyll cellse0
- Value
- 15 mMe0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gly-Gly also induced a concentration-dependent transmembrane depolarization of mesophyll cells with an apparent Michaelis constant of 15 mM”
t0“broad bean”
Claim · model-written summary
Depolarization was followed by transient hyperpolarization.
- Taxon
- broad beanVicia fabat0
- Outcome
- transient hyperpolarizatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“This depolarization was followed by a transient hyperpolarization”
t0“broad bean”
Claim · model-written summary
Several peptides and tripeptides inhibited Gly-Gly uptake at tenfold excess.
- Taxon
- broad beanVicia fabat0
- Treatment
- various peptides and tripeptidese0
- Outcome
- Gly-Gly uptakee0
- Direction
- inhibite0
- Qualifier
- 10-fold excesse0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“When present at a 10-fold excess, various peptides and tripeptides were able to inhibit Gly-Gly uptake”
t0“broad bean”
Claim · model-written summary
Gly only slightly inhibited Gly-Gly uptake.
- Taxon
- broad beanVicia fabat0
- Treatment
- Glye0
- Outcome
- uptake of Gly-Glye0
- Direction
- inhibitede0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Gly inhibited the uptake of Gly-Gly only slightly”
t0“broad bean”
Claim · model-written summary
TetraGly did not inhibit Gly-Gly uptake.
- Taxon
- broad beanVicia fabat0
- Treatment
- tetraGlye0
- Outcome
- not inhibitorye0
- Direction
- not inhibitorye0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tetraGly and the tripeptide glutathione were not inhibitory”
t0“broad bean”
Claim · model-written summary
Glutathione did not inhibit Gly-Gly uptake.
- Taxon
- broad beanVicia fabat0
- Treatment
- glutathionee0
- Outcome
- not inhibitorye0
- Direction
- not inhibitorye0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“tetraGly and the tripeptide glutathione were not inhibitory”
t0“broad bean”
Claim · model-written summary
Dipeptides that inhibited Gly-Gly uptake changed mesophyll membrane potential.
- Taxon
- broad beanVicia fabat0
- Treatment
- dipeptides inhibiting Gly-Gly uptakee0
- Outcome
- transmembrane potential difference of mesophyll cellse0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The dipeptides inhibiting Gly-Gly uptake also induced changes in the transmembrane potential difference of mesophyll cells”
t0“broad bean”
Claim · model-written summary
Dipeptides changed the membrane response normally induced by Gly-Gly.
- Taxon
- broad beanVicia fabat0
- Treatment
- dipeptidese0
- Outcome
- response normally induced by Gly-Glye0
Not reportedComparatorDirection
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The dipeptides inhibiting Gly-Gly uptake also induced changes in the transmembrane potential difference of mesophyll cells and were able to affect in a complex way the response normally induced by Gly-Gly”
t0“broad bean”
Claim · model-written summary
The data indicate a low-affinity, broad-specificity H+/peptide cotransporter in mesophyll plasma membrane.
- Taxon
- broad beanVicia fabat0
- Organ / stage
- mesophyll cellse0
- Outcome
- H+/peptide co-transportere0
- Qualifier
- low-affinity, broad-specificitye0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“existence of a low-affinity, broad-specificity H+/peptide co-transporter at the plasma membrane of mesophyll cells”
t0“broad bean”