BIOC 311 Lecture Notes - Lecture 31: Methylation, Methionine, Isoleucine
15 Dec 2015
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Document Summary
Branched-chain amino acids are not degraded in the liver. The carbon skeletons of aas vary greatly. Detailed example: methionine: provides many interesting examples of different types of reactions, defects in enzymes involved are associated with human disorders, methionine is very important in: Total of 10 reactions: 9 for degradation and 1 for regeneration (step 4) Step 1: methionine is converted into s-adenosyl-methionine (sam, catalyzed by methionine adenosyl transferase, this reaction is similar to the conversion of citrulline to citrullyl-amp intermediate catalyzed by ass. Step 2: the sulfonium group is easily attacked by nucleophiles, sam is used by methylases (>40 different reactions) Step 3: the s-adenosyl homocysteine is then hydrolyzed to release adenosine and homocysteine. Steps 5-10: targeted for degradation, transsulfuration pathway, from homocysteine to succinyl-coa. Step 5: cysteine synthesis, cysteine is a conditional essential aa, homocysteine and serine are attached together with cystathionine beta-synthase.
