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Committed step
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<h2 id="regulation">Regulation</h2> <p>Metabolic pathways require tight regulation, so that the proper compounds get produced in the proper amounts at the proper time. Often, the first committed step is regulated by processes such as <a href="/facts/Feedback_inhibition/MkFwGXHJ">feedback inhibition</a> and <a href="/facts/Activation/Gt7km0YP">activation</a>. Such regulation ensures that pathway <a href="/facts/Reaction_intermediate/BjD9HAHt">intermediates</a> do not accumulate, a situation that can be wasteful or even harmful to the cell. </p> <h2 id="examples-of-enzymes-that-catalyze-the-first-committed-steps-of-metabolic-pathways">Examples of enzymes that catalyze the first committed steps of metabolic pathways</h2> <ul><li><a href="/facts/Phosphofructokinase_1/we21cflf">Phosphofructokinase 1</a> catalyzes the first committed step of <a href="/facts/Glycolysis/a5ApxLoG">glycolysis</a>.<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li> <li>LpxC catalyzes the first committed step of <a href="/facts/Lipid_A/FlLLgd8d">lipid A</a> biosynthesis.<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li> <li><a href="/facts/8-amino-7-oxononanoate_synthase/KyKCL7rz">8-amino-7-oxononanoate synthase</a> catalyzes the first committed step in plant <a href="/facts/Biotin/WAaVxyB7">biotin</a> synthesis.<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></li> <li><a href="/facts/UDP-N-acetylglucosamine_enolpyruvyl_transferase/8kpayLjL">MurA</a> catalyzes the first committed step of <a href="/facts/Peptidoglycan/lflRRUNw">peptidoglycan</a> biosynthesis.<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></li> <li><a href="/facts/Aspartate_transcarbamoylase/b2NCoTNh">Aspartate transcarbamoylase</a> catalyzes the committed step in the <a href="/facts/Pyrimidine/uFRSB8Cq">pyrimidine</a> biosynthetic pathway in <i>E. coli</i>.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></li> <li>3-deoxy-D-arabinose-heptulsonate 7-phosphate synthase catalyses the first committed step of the shikimate pathway responsible for the synthesis of the aromatic amino acids Tyrosine, Tryptophan and Phenylalanine in plants, bacteria, fungi and some lower eukaryotes.</li> <li>Citrate synthase catalyzes the addition of <a href="/facts/Acetyl-CoA/XyxFfC84">acetyl-CoA</a> to <a href="/facts/Oxaloacetic_acid/ojLoQw81">oxaloacetate</a> and is the first committed step of the <a href="/facts/Citric_acid_cycle/EGJL9NXP">Citric Acid Cycle</a>.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a></li> <li><a href="/facts/Acetyl-CoA_carboxylase/9Lh10Lrs">Acetyl-CoA carboxylase</a> catalyzes the irreversible <a href="/facts/Carboxylation/8zNzYvnP">carboxylation</a> of <a href="/facts/Acetyl-CoA/XyxFfC84">acetyl-CoA</a> to <a href="/facts/Malonyl-CoA/n1eNlSYs">malonyl-CoA</a> in the first committed step of <a href="/facts/Fatty_acid_synthesis/Cl17j9xE">fatty acid biosynthesis</a>.</li> <li><a href="/facts/Glucose-6-phosphate_dehydrogenase/oVVtzhJB">Glucose-6-phosphate dehydrogenase</a> catalyzes the conversion of <a href="/facts/G6P/2KybIvaN">G6P</a> into <a href="/facts/6-Phosphogluconolactone/WbvG0IxG">6-phosphogluconolactone</a> to produce <a href="/facts/NADPH/XMgmPQ5t">NADPH</a> in the first and committed step of the <a href="/facts/Pentose_phosphate_pathway/NbuG6Ffj">pentose phosphate pathway</a>.</li></ul> <h2 id="other-uses">Other uses</h2> <p>The term has also been applied to other processes that involve a series of steps. For example, the binding of egg and sperm can be thought of as the first committed step in <a href="/facts/Metazoan/4b8J33nd">metazoan</a> <a href="/facts/Fertilization/g8u3UKzF">fertilization</a>.<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a> </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Enzyme_catalysis/4a283vgL">Enzyme catalysis</a></li> <li><a href="/facts/Negative_feedback/G9byVgpN">Negative feedback</a></li> <li><a href="/facts/Metabolic_control_analysis/Y9sKWSJ7">Metabolic Control Analysis</a></li></ul> <h2 id="external-links">External links</h2> <ul><li><a href="https://web.archive.org/web/20110918042851/http://www.cliffsnotes.com/study_guide/Glycolysis-Regulation.topicArticleId-24998,articleId-24983.html"><i>Glycolysis Regulation</i></a> at Cliffsnotes.com</li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Bhagavan, N. V. (2002). Medical biochemistry. San Diego: Harcourt/Academic Press. ISBN 0-12-095440-0. <a href="0-12-095440-0" target="_blank">0-12-095440-0</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>Berg, Jeremy M.; Tymoczko, John L.; Stryer, Lubert (2002). Biochemistry (5th ed.). W. H. Freeman and Company. p. 447. ISBN 0-7167-3051-0. <a href="0-7167-3051-0" target="_blank">0-7167-3051-0</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Sauro, Herbert M. (February 2017). "Control and regulation of pathways via negative feedback". Journal of the Royal Society Interface. 14 (127): 20160848. doi:10.1098/rsif.2016.0848. PMC 5332569. PMID 28202588. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5332569" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5332569</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Hofmeyr, Jan-Hendrik S.; Cornish-Bowden, Athel (August 1991). "Quantitative assessment of regulation in metabolic systems". European Journal of Biochemistry. 200 (1): 223–236. doi:10.1111/j.1432-1033.1991.tb21071.x. PMID 1879427. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>"Phosphofructokinase Regulation". Wiley Essential Biochemistry. Retrieved 17 February 2010. <a href="http://www.wiley.com/college/pratt/0471393878/student/structure/phosphofructokinase/index.html" target="_blank">http://www.wiley.com/college/pratt/0471393878/student/structure/phosphofructokinase/index.html</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>Raetz C, Whitfield C (2002). "Lipopolysaccharide endotoxins". Annu Rev Biochem. 71: 635–700. doi:10.1146/annurev.biochem.71.110601.135414. PMC 2569852. PMID 12045108. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569852" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2569852</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li> <li id="fn:7"><p>Pinon V, Ravanel S, Douce R, Alban C (2005). "Biotin synthesis in plants. The first committed step of the pathway is catalyzed by a cytosolic 7-keto-8-aminopelargonic acid synthase". Plant Physiology. 139 (4): 1666–76. doi:10.1104/pp.105.070144. PMC 1310550. PMID 16299174. <a href="http://www.plantphysiol.org/cgi/content/full/139/4/1666" target="_blank">http://www.plantphysiol.org/cgi/content/full/139/4/1666</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li> <li id="fn:8"><p>Brown ED, Vivas EI, Walsh CT, Kolter R (July 1995). "MurA (MurZ), the enzyme that catalyzes the first committed step in peptidoglycan biosynthesis, is essential in Escherichia coli". J. Bacteriol. 177 (14): 4194–7. doi:10.1128/jb.177.14.4194-4197.1995. PMC 177162. PMID 7608103. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC177162" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC177162</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li> <li id="fn:9"><p>Berg, Jeremy M.; Tymoczko, John L.; Stryer, Lubert (2002). Biochemistry (5th ed.). W. H. Freeman and Company. p. 447. ISBN 0-7167-3051-0. <a href="0-7167-3051-0" target="_blank">0-7167-3051-0</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li> <li id="fn:10"><p>Biochemistry & molecular biology of plants. Bob B. Buchanan, Wilhelm Gruissem, Russell L. Jones. Rockville, Md.: American Society of Plant Physiologists. 2000. ISBN 0-943088-37-2. OCLC 44162497.{{cite book}}: CS1 maint: others (link) <a href="0-943088-37-2" target="_blank">0-943088-37-2</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></p></li> <li id="fn:11"><p>Dell A, Chalabi S, Easton RL, et al. (December 2003). "Murine and human zona pellucida 3 derived from mouse eggs express identical O-glycans". Proc. Natl. Acad. Sci. U.S.A. 100 (26): 15631–6. Bibcode:2003PNAS..10015631D. doi:10.1073/pnas.2635507100. PMC 307619. PMID 14673092. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC307619" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC307619</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></p></li> </ol>