Proton/L-glutamate symport and the regulation of intracellular pH in isolated mesophyll cells

Addition of L-[U-14C]glutamate to a suspension of mechanically isolated asparagus (Asparagus sprengeri Regel) mesophyll cells results in (a) alkalinization of the medium, (b) uptake of L-[U-14C] glutamate, and (c) efflux of [14C]4-aminobutyrate, a product of glutamate decarboxylation. All three phen...

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Bibliographic Details
Published in:Plant physiology (Bethesda) 1992-06, Vol.99 (2), p.665-671
Main Authors: Snedden, W.A. (University of Guelph, Guelph, Ontario), Chung, I, Pauls, R.H, Bown, A.W
Format: Article
Language:English
Subjects:
ACETATE
ACETATOS
ACIDE GLUTAMIQUE
ACIDIFICACION
ACIDIFICATION
ACIDO GLUTAMICO
Amino acids
ASPARAGUS
Asparagus sprengeri
Biological and medical sciences
BUTIRATOS
BUTYRATE
Cell physiology
Chemical suspensions
Decarboxylation
FISIOLOGIA VEGETAL
Fundamental and applied biological sciences. Psychology
GLUTAMATE DECARBOXYLASE
GLUTAMATO DECARBOXILASA
glutamic acid
INHIBIDORES DE ENZIMAS
INHIBITEUR D'ENZYME
ION
IONES
mechanisms
MESOFILO
Mesophyll cells
MESOPHYLLE
Physiological regulation
PHYSIOLOGIE VEGETALE
Plant physiology and development
Plants
Plasma membrane and permeation
Protons
regulation
transport
VIA BIOQUIMICA DEL METABOLISMO
VOIE BIOCHIMIQUE DU METABOLISME
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Summary:Addition of L-[U-14C]glutamate to a suspension of mechanically isolated asparagus (Asparagus sprengeri Regel) mesophyll cells results in (a) alkalinization of the medium, (b) uptake of L-[U-14C] glutamate, and (c) efflux of [14C]4-aminobutyrate, a product of glutamate decarboxylation. All three phenomena were eliminated by treatment with 1 millimolar aminooxyacetate. In vitro glutamate decarboxylase (GAD) assays showed that (a) 2 millimolar aminooxyacetate eliminated enzyme activity, (b) activity was pyridoxal phosphate-dependent, and (c) activity exhibited a sharp pH optimum at 6.0 that decreased to 20% of optimal activity at pH 5.0 and 7.0. Addition of 1.5 millimolar sodium butyrate or sodium acetate to cell suspensions caused immediate alkalinization of the medium followed by a resumption of acidification of the medium at a rate approximately double the initial rate. The data indicate that (a) continued H+/L-glutamate cotransport is dependent upon GAD activity, (b) the pH-dependent properties of GAD are consistent with a role in a metabolic pH-stat, and (c) the regulation of intracellular pH during H+/L-Glu symport may involve both H+ consumption during 4-aminobutyrate production and ATP-driven H+ efflux
ISSN:0032-0889
1532-2548
DOI:10.1104/pp.99.2.665