Effect of phosphate and uncouplers on substrate transport and oxidation by isolated corn mitochondria

Journal Article · Tue Feb 01 04:00:00 EST 1977 · Plant Physiol.; (United States)

DOI:https://doi.org/10.1104/pp.59.2.139· OSTI ID:5276831

Day, D A; Hanson, J B

A study was made to determine conditions under which malate oxidation rates in corn (Zea mays L.) mitochondria are limited by transport processes. In the absence of added ADP, inorganic phosphate increased malate oxidation rates by processes inhibited by mersalyl and oligomycin, but phosphate did not stimulate uncoupled respiration. However, the uncoupled oxidation rates were inhibited by butylmalonate and mersalyl. When uncoupler was added prior to substrate, subsequent O/sub 2/ uptake rates were reduced when malate and succinate, but not exogenous NADH, were used. Uncoupler and butylmalonate also inhibited swelling in malate solutions and malate accumulation by these mitochondria, which were found to have a high endogenous phosphate content. Addition of uncoupler after malate or succinate produced an initial rapid oxidation which declined as the mitochondria lost solute and contracted. This decline was not affected by addition of ADP or AMP, and was not observed when exogenous NADH was substrate. Increasing K/sup +/ permeability with valinomycin increased the P-trifluoromethoxy (carboxylcyanide)phenyl hydrazone inhibition. Kinetic studies showed the slow rate of malate oxidation in the presence of uncoupler to be characterized by a high Km and a low V/sub max/, probably reflecting a diffusion-limited process. The results indicate that rapid malate and succinate oxidation require the operation of both the phosphate and dicarboxylate transporters, which in turn depend on maintenance of a proton motive force across the inner membrane. In addition, phosphate can stimulate acceptorless malate oxidation by reaction with the coupling mechanism, and in uncoupled mitochondria which are depleted of substrate there is a slow rate of oxidation which appears to be limited by diffusive entry.

• Research Organization: Univ. of Illinois, Urbana
• OSTI ID: 5276831
• Journal Information: Plant Physiol.; (United States), Journal Name: Plant Physiol.; (United States) Vol. 59:2; ISSN PLPHA
• Country of Publication: United States
• Language: English

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59 BASIC BIOLOGICAL SCIENCES
ADP
ALKALI METALS
AMINO ACIDS
AMP
BIOCHEMISTRY
BIOLOGICAL EFFECTS
BIOMASS
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CEREALS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CHEMISTRY
CRYOGENIC FLUIDS
DICARBOXYLIC ACIDS
ELEMENTS
ENERGY SOURCES
ESTERS
FLUIDS
GRAMINEAE
GRASS
HYDROXY ACIDS
KINETICS
MAIZE
MALIC ACID
MEMBRANES
METALS
MITOCHONDRIA
NONMETALS
NUCLEOTIDES
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANOIDS
OXIDATION
OXYGEN
OXYGEN COMPOUNDS
PERMEABILITY
PHOSPHATES
PHOSPHORUS COMPOUNDS
PLANTS
POTASSIUM
REACTION KINETICS
RENEWABLE ENERGY SOURCES
RESPIRATION
SUCCINIC ACID
UPTAKE
VALINE