From owner-metabolic-reg@net.bio.net Tue May 09 23:00:00 1995 Path: biosci!rutgers!gatech!howland.reston.ans.net!xlink.net!rz.uni-karlsruhe.de!news.uni-ulm.de!news.belwue.de!news.belwue.de!news.uni-konstanz.de!schink From: Andreas.Brune@uni-konstanz.de (Andreas Brune) Newsgroups: bionet.metabolic-reg Subject: Re: Q: glycolysis and respiration? Date: Wed, 10 May 95 14:14:21 GMT Organization: Universitaet Konstanz Lines: 42 Distribution: world Message-ID: <3oqhnt$qus_001@news.uni-konstanz.de> References: <3ojn6t$leg@decaxp.harvard.edu> NNTP-Posting-Host: schink.biologie.uni-konstanz.de Keywords: glycolysis, citric acid cycle, Krebs cycle, respiration, oxidative phosphorylation X-Newsreader: News Xpress Version 1.0 Beta #3 In article <3ojn6t$leg@decaxp.harvard.edu>, Zorro wrote: > >I recently read in a popular book on exercising that muscles could not >burn fatty acids without first burning glucose. >.... >I haven't been able to find confirmation to any of the above in my >biochemistry textbooks. As far as I can tell, fatty acid oxidation, >the citric acid cycle, and oxidative phosphorylation can all take >place *without* any prior or concomitant glycolysis. Is this true? >Or I'm I missing something? On a piece of paper you can indeed oxidize acetyl-CoA to 2 CO2 via the TCA cycle (and reoxidize the coenzymes via the respiratory chain...). However, you should consider that the TCA cycle is the metabolic turntable of the cell -- besides its catabolic function it serves as a continous source for building blocks in anabolism (C4 and C5 compounds, and C3 via decarboxylation of C4 compounds). This depletes the cycle of C4 compounds which have to be replenished by so-called anaplerotic reactions. In humans, this is done by carboxylation of a C3 to a C4 compound (by pyruvate carboxylase). Since humans are unable to go from C2 to C3 directly (i.e., by carboxylation of acetyl-CoA) and since they also can't combine 2 acetyl-CoA to a C4 compound (like plants do in the glyoxylic acid cycle), the TCA cycle will run out of intermediates if no additional C3 compounds are supplied by glycolysis. This is a quite simplified explanation why "fats burn in the fire of carbohydrates", a phenomenon already observed in the last century. I didn't bother to mention the names for all the compounds with 2, 3 or 4 carbon atoms since they're unnecessary details (unnecessary for a brief answer to this question, i mean ;-) Regards, Andreas Dr. Andreas Brune Phone: +49-7531-883282 Mikrobielle Oekologie Fax: +49-7531-882966 Universitaet Konstanz E-mail: Andreas.Brune@uni-konstanz.de .