Mechanisms of citrate transport and exchange in corn mitochondria

Journal Article · Sat Jan 01 04:00:00 EST 1983 · Plant Physiol.; (United States)

DOI:https://doi.org/10.1104/pp.71.4.803· OSTI ID:5127393

Birnberg, P R; Hanson, J B

Previous work demonstrated that corn mitochondria (Zea mays L.) can accumulate citrate by a malate- and phosphate-independent proton symporter. This uptake and symport of other ions were investigated. Isocitrate is a competitive inhibitor of citrate uptake and (/sup 14/C)isocitrate is accumulated with a K/sub m/ similar to its I/sub 50/. Valinomycin reduces net active citrate accumulation at pH 7.5, consistent with the relatively low V/sub max/ for citrate uptake. At pH 4.5, mersalyl reduces the rate of citrate uptake without changing the affinity of the carrier for citrate. Thus, the corn mitochondria have a high-affinity, mersalyl-insensitive carrier selective for citrate that also transports isocitrate. The pH optimum for oxidation of both endogenous substrates and citrate is approximately pH 6.8. Under active conditions only, at pH 7.0, malate/citrate exchange occurs with 4 millimolar malate being sufficient to remove about half the matrix citrate. Therefore, in vivo both citrate uptake by proton symport and efflux by malate/citrate exchange should occur, with the net direction of citrate movement determined by the cytoplasmic pH, and citrate and malate concentrations; in most cases, net efflux is likely to be favored.

• Research Organization: Univ. of Illinois, Urbana
• DOE Contract Number: AC02-76EV00790
• OSTI ID: 5127393
• Journal Information: Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 71; ISSN PLPHA
• Country of Publication: United States
• Language: English

Related Subjects

550300* -- Cytology
59 BASIC BIOLOGICAL SCIENCES
ANIONS
BIOCHEMICAL REACTION KINETICS
CARBON 14 COMPOUNDS
CARBOXYLIC ACID SALTS
CELL CONSTITUENTS
CEREALS
CHARGED PARTICLES
CHEMICAL REACTIONS
CITRATES
GRASS
INHIBITION
IONS
KINETICS
LABELLED COMPOUNDS
MAIZE
MEMBRANE TRANSPORT
MITOCHONDRIA
ORGANOIDS
OXIDATION
PH VALUE
PLANTS
REACTION KINETICS