Energetics of Proline Transport in Corn Mitochondria

Elthon, Thomas E.; Stewart, Cecil R.; Bonner, Walter D.

doi:10.1104/pp.75.4.951

Cited by 10 publications

(3 citation statements)

References 14 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The mitochondrial localization of both ProDH and P5CDH (Adams and Frank 1980;Elthon and Stewart 1982;Elthon et al 1984) poses the question as to how Pro, which is both produced and/or transported to the cytosol, can cross the mitochondrial membrane. As an initial approach to this problem, swelling experiments were carried out with a particular focus on stereospecificity.…”

Section: Resultsmentioning

confidence: 99%

Mitochondrial transport in proline catabolism in plants: the existence of two separate translocators in mitochondria isolated from durum wheat seedlings

Martino

Pizzuto

Pallotta

et al. 2005

Planta

View full text Add to dashboard Cite

Abiotic stresses, such as high salinity or drought, can cause proline accumulation in plants. Such an accumulation involves proline transport into mitochondria where proline catabolism occurs. By using durum wheat seedlings as a plant model system, we investigated how proline enters isolated coupled mitochondria. The occurrence of two separate translocators for proline, namely a carrier solely for proline and a proline/glutamate antiporter, is shown in a functional study in which we found the following: (1) Mitochondria undergo passive swelling in isotonic proline solutions in a stereospecific manner. (2) Externally added L: -proline (Pro) generates a mitochondrial membrane potential (Delta Psi) with a rate depending on the transport of Pro across the mitochondrial inner membrane. (3) The dependence of the rate of generation of Delta Psi on increasing Pro concentrations exhibits hyperbolic kinetics. Proline transport is inhibited in a competitive manner by the non-penetrant thiol reagent mersalyl, but it is insensitive to the penetrant thiol reagent N-ethylmaleimide (NEM). (4) No accumulation of proline occurs inside the mitochondria as a result of the addition of proline externally, whereas the content of glutamate increases both in mitochondria and in the extramitochondrial phase. (5) Glutamate efflux from mitochondria occurs at a rate which depends on the mitochondrial transport, and it is inhibited in a non-competitive manner by NEM. The dependence of the rate of glutamate efflux on increasing proline concentration shows saturation kinetics. The physiological role of carrier-mediated transport in the regulation of proline catabolism, as well as the possible occurrence of a proline/glutamate shuttle in durum wheat seedlings mitochondria, are discussed.

show abstract

Section: Resultsmentioning

confidence: 99%

Mitochondrial transport in proline catabolism in plants: the existence of two separate translocators in mitochondria isolated from durum wheat seedlings

Martino

Pizzuto

Pallotta

et al. 2005

Planta

View full text Add to dashboard Cite

show abstract

“…The mitochondrial preparations were confirmed to be transport-competent by supplying [ 3 H]proline in place of [ 3 H]pABA-Glc (Fig. 5D); proline is known to be readily taken up by energized plant mitochondria (31).…”

Section: Resultsmentioning

confidence: 99%

Metabolism of the Folate Precursor p-Aminobenzoate in Plants

Eudes

Bozzo

Waller

et al. 2008

Journal of Biological Chemistry

View full text Add to dashboard Cite

Plants produce p-aminobenzoate (pABA) in chloroplasts and use it for folate synthesis in mitochondria. In plant tissues, however, pABA is known to occur predominantly as its glucose ester (pABA-Glc), and the role of this metabolite in folate synthesis has not been defined. In this study, the UDP-glucose:pABA acylglucosyltransferase (pAGT) activity in Arabidopsis extracts was found to reside principally (95%) in one isoform with an apparent K m for pABA of 0.12 mM. Screening of recombinant Arabidopsis UDP-glycosyltransferases identified only three that recognized pABA. One of these (UGT75B1) exhibited a far higher k cat /K m value than the others and a far lower apparent K m for pABA (0.12 mM), suggesting its identity with the principal enzyme in vivo. Supporting this possibility, ablation of UGT75B1 reduced extractable pAGT activity by 95%, in vivo [ 14 C]pABA glucosylation by 77%, and the endogenous pABAGlc/pABA ratio by 9-fold. The K eq for the pABA esterification reaction was found to be 3 ؋ 10 ؊3 . Taken with literature data on the cytosolic location of pAGT activity and on cytosolic UDPglucose/UDP ratios, this K eq value allowed estimation that only 4% of cytosolic pABA is esterified. That pABA-Glc predominates in planta therefore implies that it is sequestered away from the cytosol and, consistent with this possibility, vacuoles isolated from [ 14 C]pABA-fed pea leaves were estimated to contain >88% of the [ 14 C]pABA-Glc formed. In total, these data and the fact that isolated mitochondria did not take up [ 3 H]pABAGlc, suggest that the glucose ester represents a storage form of pABA that does not contribute directly to folate synthesis.

show abstract

“…T4C Survival Assay-T4C competes with Pro in the translation process (42,43) and can be degraded by Pro dehydrogenase in plants and bacteria (44,45). One-week-old WT and ProDH-OE tobacco seedlings (T 2 ) were transferred to MS medium containing 50 mM NaCl, 3 mM T4C, or 50 mM NaCl ϩ 3 mM T4C.…”

Section: Methodsmentioning

confidence: 99%

Unraveling Δ1-Pyrroline-5-Carboxylate-Proline Cycle in Plants by Uncoupled Expression of Proline Oxidation Enzymes

Miller

Honig

Stein

et al. 2009

Journal of Biological Chemistry

228

221

View full text Add to dashboard Cite

The two-step oxidation of proline in all eukaryotes is performed at the inner mitochondrial membrane by the consecutive action of proline dehydrogenase (ProDH) that produces ⌬ 1 -pyrroline-5-carboxylate (P5C) and P5C dehydrogenase (P5CDH) that oxidizes P5C to glutamate. This catabolic route is down-regulated in plants during osmotic stress, allowing free Pro accumulation. We show here that overexpression of MsProDH in tobacco and Arabidopsis or impairment of P5C oxidation in the Arabidopsis p5cdh mutant did not change the cellular Pro to P5C ratio under ambient and osmotic stress conditions, indicating that P5C excess was reduced to Pro in a mitochondrial-cytosolic cycle. This cycle, involving ProDH and P5C reductase, exists in animal cells and now demonstrated in plants. As a part of the cycle, Pro oxidation by the ProDH-FAD complex delivers electrons to the electron transport chain. Hyperactivity of the cycle, e.g. when an excess of exogenous L-Pro is provided, generates mitochondrial reactive oxygen species (ROS) by delivering electrons to O 2 , as demonstrated by the mitochondria-specific MitoSox staining of superoxide ions. Lack of P5CDH activity led to higher ROS production under dark and light conditions in the presence of Pro excess, as well as rendered plants hypersensitive to heat stress. Balancing mitochondrial ROS production during increased Pro oxidation is therefore critical for avoiding Pro-related toxic effects. Hence, normal oxidation of P5C to Glu by P5CDH is key to prevent P5C-Pro intensive cycling and avoid ROS production from electron run-off.Stress-related changes in Pro biosynthesis and degradation are conserved in different organisms and used to induce essential signaling pathways, such as p53-mediated apoptosis in mammalian cells (1) or osmo-protecting mechanisms in plants (2) and bacteria (3). Pro is one of the most common osmolytes that, together with glycine-betaine and soluble sugars, accumulates in plants in response to a wide array of abiotic and biotic stresses (2,4,5). Although the role of Pro as an osmo-protecting molecule in prokaryotes is well established (3, 6), the overall function of stress-accumulated free Pro in plants is still under debate (2, 7-9). In most plants, stress-induced free Pro accumulation results from enhanced Pro synthesis and concomitant silencing of Pro degradation (10 -13). Pro is produced in the cytosol and chloroplasts (14, 15) and degraded in the mitochondria by a short, strictly regulated cyclic pathway (Fig. 1). In the anabolic part of the pathway, glutamate is converted to ⌬ 1 -pyrroline-5-carboxylate (P5C) 3 by P5C synthetase (P5CS), and P5C-reductase (P5CR) reduces P5C to Pro. In an alternative pathway, P5C is generated from ornithine by mitochondrial ornithine-aminotransferase (16, 17) and is reduced to Pro by P5CR in the cytosol. Thus, a possible movement of P5C among organelles and cytosol is assumed. P5CS is considered the key enzyme in the synthesis route, and its expression is increased by osmotic stress in many plants (11, 16 -18). A singl...

show abstract

Energetics of Proline Transport in Corn Mitochondria

Cited by 10 publications

References 14 publications

Mitochondrial transport in proline catabolism in plants: the existence of two separate translocators in mitochondria isolated from durum wheat seedlings

Mitochondrial transport in proline catabolism in plants: the existence of two separate translocators in mitochondria isolated from durum wheat seedlings

Metabolism of the Folate Precursor p-Aminobenzoate in Plants

Unraveling Δ1-Pyrroline-5-Carboxylate-Proline Cycle in Plants by Uncoupled Expression of Proline Oxidation Enzymes

Contact Info

Product

Resources

About