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Title: USE OF SULFHYDRYL-DIRECTED INHIBITORS IN VITRO TO DISTINGUISH ACTIVITIES OF THE MITOCHONDRIAL AND PLASTIDIC FORMS OF PYRUVATE DEHYDROGENASE

Author
item JOHNSTON, MARK - UNIV OF MISSOURI-COLUMBIA
item Miernyk, Jan
item RANDALL, DOUGLAS - UNIV OF MISSOURI-COLUMBIA

Submitted to: Archives of Biochemistry and Biophysics
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/2/2000
Publication Date: 6/30/2000
Citation: Johnston, M.L., Miernyk, J.A., Randall, D.D. 2000. Use of sulfhydryl-directed inhibitors in vitro to distinguish activities of the mitochondrial and plastidic forms of pyruvate dehydrogenase. Archives Of Biochemistry And Biophysics. V.378(1):192-193.

Interpretive Summary: Respiration is the use of energy by living cells to do work. Both growth and reproduction are affected by respiration. As a result, respiration must be carefully controlled or wasted energy would decrease crop yields and reduce agricultural productivity. The control of respiration in plant cells is a subject of ongoing study. A protein that is important in the regulation of respiration was isolated from pea seedlings and studied. Comparisons were made with a similar protein from animals and microbes in order to predict characteristics that might be important in control of respiration. A method was developed to test these predictions by reaction with specific chemical agents. This information will be important to researchers in their attempts to increase agricultural productivity by altering the control of plant cell respiration, and to other scientists who will try to design more efficient crop plants through either classical plant breeding or biotechnology.

Technical Abstract: Inhibition by sulfhydryl-directed reagents is one of the criteria used to establish the occurrence of an "essential cysteine residue" in the E1alpha subunit of mammalian mitochondrial pyruvate dehydrogenase. Inhibition of pea (Pisum sativum L.) mitochondrial pyruvate dehydrogenase activity in vitro by treatment with iodoacetate, iodoacetamide, or N-ethylmaleimide extends the mammalian model. In contrast, the in vitro activity of pea chloroplast pyruvate dehydrogenase was unaffected by the sulfhydryl-directed inhibitors. Chemical modification and site-directed mutagenesis had been used to identify the essential cysteine residue of mammalian pyruvate dehydrogenase as "Cys62." In plastidic E1alpha sequences, this otherwise highly conserved cysteine residue is replaced with a valine, providing an explanation for the insensitivity to sulfhydryl-directed inhibitors.