Lecture 11-10 - Nitrogen Metabolism-Ch. 15 Nitrogen...

Info iconThis preview shows pages 1–5. Sign up to view the full content.

View Full Document Right Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Nitrogen Metabolism-Ch. 15 Nitrogen Fixation and assimilation nitrogen moves through the food chain from N 2-->NH 3--->organic compounds nitrogen fixation--reduction of N 2-->NH 3 o can only be carried out by a few microorgansims Rhizobium-- symbiotes of leguminous plants (beans, clover, alfalfa, peas) Azotobacter, Klebsiella, Clostritium and cyanobacteria (aquatic)--free living bacteria o these organisms contain the enzyme system for the reduction of N 2-->NH 3--- nitrogenase complex NITROGEN CYCLE Nitrogenase -- nitrogen fixation o nitrogenase--uses electrons (from ferredoxin) to reduce N 2-->NH 3 via a Fe-Mb center o expensive process-- consumes ATP (20-30) Nitrate reductase--plants, fungi, some bacteria o conversion of nitrate to nitrite Nitrite reductase o conversion of nitrite to ammonia Ammonia Assimilation conversion of ammonia to organic nitrogen two reactions: catalyzed by different enzymes (similar names though....) o glutamine synthetase--present in all organisms--uses energy and is irreversible glutamate + NH 4 + + ATP------> glutamine + ADP + Pi o glutamate synthase--bacteria, plants--not present in mammals -ketoglutarate + glutamine + NADPH <---> 2glutamate + NADP + o glutamine and glutamate are nitrogen "carriers" -- generally higher concentrations than other AA o used for the synthesis of other nitrogen containing compounds: amino acids, purines, pyrimidines Transamination--transfer of an amino group from an alpha amino acid to an -keto acid generating a new amino acid/ -keto acid Pyridoxal Phosphate vitamin B6 cofactor for transaminations attached to enzyme via Schiff's base to lysine in active site Glutamate is key intermediate transferring its amino group to other keto acids: pyruvate + glutamate --> alanine + -ketoglutarate oxaloacetate + glutamate --> aspartate + -ketoglutarate lysine cannot be formed by this method, the keto acid intermediate is unstable all transaminase reactions use enzyme bound pyridoxal phosphate (PLP) as a coenzyme "holder" of the amino group o forms Schiff's base linkage Mechanism of transaminases-- see detailed mechanism in Fig. 15-5 enzyme lysine in active site forms Schiff base with PLP formation of covalent bond between pyridoxal phosphate and - amino group of amino acid --forms new Schiff base with aa, releases enzyme lysine lysine residue abstracts hydrogen from substrate - carbon causing rearragement of double bond hydrolysis releases the keto acid and the pyridoxalamine form of cofactor the keto acid leaves the active site and is replaced by another keto acid all the steps are reversed, the pyridoxalamine donates the amino group to the new keto acid, generating a new amino acid and regenerating the enzyme bound form of pyridoxal phosphate these reactions are reversible and proceed in the direction of the substrate availability transaminases are also markers of tissue damage following heart attack or for liver damage Amino Acid Bioynthesis...
View Full Document

This note was uploaded on 12/31/2010 for the course CH 369 taught by Professor Kbrowning during the Spring '07 term at University of Texas at Austin.

Page1 / 33

Lecture 11-10 - Nitrogen Metabolism-Ch. 15 Nitrogen...

This preview shows document pages 1 - 5. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online