Bioenergetics of proline oxidation and related processes in plant mitochondria

Elthon, Thomas
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A model which provides a balanced application of chemiosmosis to plant mitochondria is presented. In this model, the electron transport chain carriers are sequenced to achieve proton translocation across the inner membrane. In addition, the processes of proton translocation, utilization, and release are integrated to yield a description of the effective proton gradient available for metabolite transport and ATP synthesis;Proline dependent O(,2) uptake in corn mitochondria was investigated and found to occur through a proline DH (dehydrogenase) bound to the matrix side of the inner mitochondrial membrane. This DH activity did not involve NAD reduction, and thus electrons and protons entered the respiratory chain directly. P5C ((DELTA)('1)-pyrroline-5-carboxylate) derived from proline was oxidized by a P5C DH that was similar to proline DH in that it was bound to the matrix side of the inner membrane and fed electrons and protons directly into the respiratory chain. Ornithine dependent O(,2) uptake was measurable in corn mitochondria and resulted from an ornithine transaminase coupled with a P5C DH. These enzymes existed as a complex bound to the matrix side of the inner membrane;The effect of various proline analogs on proline oxidation in mitochondria isolated from etiolated barley (Hordeum vulgare) shoots was investigated. Of the analogs tested, only T4C (L-thiazolidine-4-carboxylic acid) was effective. T4C (1 mM) inhibited proline (10 mM) dependent O(,2) uptake an average of 67%. The effect of T4C on the oxidation of other mitochondrial substrates was also tested. T4C inhibited P5C dependent O(,2) uptake slightly (13%), the oxidation of malate + pyruvate even less (6%), and stimulated the oxidation of succinate (+11%), exogenous NADH (+19%), and citrate (+20%). The effect of T4C on proline metabolism in detached green barley leaves was also investigated. T4C inhibited proline oxidation in turgid leaves, and increased the proline content of these leaves slightly. In wilted leaves (that are synthesizing proline rapidly), T4C inhibited proline synthesis, which resulted in a decrease in the proline content. T4C had no influence on proline incorporation into protein.

Botany, Botany (Physiology), Physiology