Amino acids that generate fumarate

phenylalnine  and tyrosine are catabolism by a commo pathway the partial degradation of these two amino acids produces two products ,fumarate and acetoacetate both of which can enter the TCA cycle. Acetoacetate is a ketone body that is activated to acetoacetyl COAand then cleaved to acetylCOA for further catabolism.

   

phenylalanine ,an essential amino acids is first converted into tyrosine by phenylalanine hydroxylase (phenylalanine monoxygenase). this reaction requires the cofactor ,tetrahydrobiopterin unconjugated pterin) and oxygen. in the hydoxylation of phenylalanine the cofactor,is oxidised to dihydrobiopterin which reduces the second atom of oxygen to water.the cofactor is reduced back to THB by dihydrobiopterin reductase. this reaction not only provides the amino acids tyrosine but is also a common degradation route of both amino acids from this point onwards.  

In this next steps ,tyrosine is transaminases to p-hydroxyphenylpyruvate by tyrosine aminotransferase.this is followed by two dioxygenase generates the familiar intermadiate ,homogentisic acids by bringing about oxidative decarboxylation, ring hydroxylationand migration of the side chain. the second dioxygenase oxidises the  substrate and cleaves the aromatic ring producing 4-maleylacetoacetate. A dioxygenase enzyme add both atoms of oxygen to the substrate and also brings ring cleavage ,if required. the active site of these enzymes contain iron. 

isomerization of 4-maleylacetoacetate to 4-fumarylacetate is catalysed by maleyacetoacetate isomerase which requires glutathione as a cofactor. finally hydrolytic cleavage of fumarylaceacetate by fumarylaceacetate yields acetoacetate and fumarate.

Amino Acids That Converted To Succinyl COA

Methionine ,valine isoleucine and theronine converge at some point in their catabolism to form succinyl COA as one of the produces. an overview of the products an overview of the common catabolic route is depicted in the pathways of methionine and theronine are linked at the point of a- ketobutyrate whereas isoleucine and valine produce propionyl COA subsequently a ketobutyrate is also converted to propionyl-COA. the latter enters the TCA cycle after a three steps transformation to succinyl-COA.

we shall now describe in some details the catabolism of these four amino acids begining with methionine the pathways of methionine catabolism in animals is also the route for cysteine biosynthesis and activated one carbon donor ,s-adenosyl methionine (SEM). the activated methyl cycle operateswith the first three enzyme of methionine catabolism and methionine catabolism and methionine synthesis  most biological methyl transfers reaction utilise SAM.it is much more reactive than n5 methyl due the presence of positively charged sulphonium ions.