Amino_Acid_Synthesis

Convert n2 to ammonium ion ammonium

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Unformatted text preview: NOT used to drive an unfavorable process, its [email protected] is to lower [email protected]@on energy. ATP hydrolysis changes [email protected] of the reductase to facilitate transfer of electrons to dinitrogenase in a manner similar to GTP hydrolysis in G proteins. ATP binding lowers the [email protected] [email protected] of the 4Fe ­4S center in reductase and brings reductase physically closer to dinitrogenase. Refer to Figure 22 ­3 on p. 855 for [email protected] of subunits and co ­ factors. Nitrogenase complex can be irreversibly [email protected] by molecular oxygen. Many organisms have developed [email protected] mechanisms to exclude O2 or become reversibly inhibited by O2 to protect their nitrogenase from irreversible [email protected]@on. In root nodules of legumes, nitrogen ­fixing bacteria invade the cells in the roots to provide ammonium ions from molecular nitrogen. In a [email protected] [email protected], the legume plant synthesizes leghemoglobin to bind O2 with high affinity to prevent [email protected]@on of nitrogenase complex. To introduce ammonium ions into more complex biological molecules, bacteria and plants [email protected] a [email protected] of glutamate synthase and glutamine synthetase to catalyze the following [email protected]: Glutamate synthase: α ­ketoglutarate + glutamine + NADPH + H+ → 2 glutamate + NADP+ Glutamine synthetase: glutamate + NH4+ + ATP → glutamine + ADP + Pi + H + Overall: α ­ketoglutarate + NH4+ + ATP +NADPH → glutamate + NADP+ + ADP + Pi The combined [email protected] of glutamate synthase and glutamine synthetase allow bacteria and plants to incorporate ammonium ions with keto acids to make amino acids. However, animals do not have glutamate synthase. In other words, we really don’t have the capability for net [email protected] of ammonium ions to amino acids. Even the [email protected] amino acids that we can synthesize and thus not needed in the diet require [email protected] amino acids in the diet to provide ammonium ions through aminotransferases. (Refer to your textbook for discussion on reverse [email protected] of glutamate dehydrogenase on p. 857.) Biosynthesis of amino acids requires precursors that are intermediates in many metabolic pathways including pentose phosphate pathway (both [email protected] and non ­[email protected]), glycolysis, and citric acid cycle. For example, synthesis of [email protected] amino acids requires both PEP from glycolysis and erythrose 4 ­phosphate from non ­[email protected] phase of PPP. Biosynthesis of just about every amino acid requires transfer of amino group from glutamate or amide group from glutamine. Transfer of amino group from glutamate requires an aminotransferases. Transfer of amide group from glutamine requires glutamine amidotransferases (above). Synthesis of [email protected] amino acids in plants requires chorismate, a product of the shikimate pathway. The [email protected] ingredient of the herbicide Round ­up is glycine phosphate, or glyphosate, is a [email protected] state analogue occupying the phosphoenolpyruvate binding site of 5 ­enolpyruvylshikimate 3 ­phosphate synthase. Glycine and succinyl ­CoA are required for synthesis of heme. The point of this slide is to demonstrate the importance of amino acids in the synthesis of many biologically important molecules. No need to memorize the pathway. [email protected] in the porphyrin synthesis pathway lead to porphyria, diseases characterized by neurological [email protected] and intense abdominal pain. Biliverdin, the breakdown product of heme catalyzed by heme oxygenase, is a powerful an@ ­ oxidant. Bilibrubin is also a strong an@ ­oxidant. Urobilin is the source of the yellow color in urine. [email protected], the short ­term reserve of high ­energy phosphate compounds, is derived from three different amino acids. Amino acids are precursors of many signaling molecules. Examples include neurotransmihers, adrenal hormones norepinephrine and epinephrine, and nitric oxide....
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This note was uploaded on 09/19/2013 for the course BIOC 462b taught by Professor Grimes,tsao,borque during the Spring '08 term at Arizona.

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