Methionine metabolism
Methionine metabolism.
The first step in (L)-Methionine metabolism, the synthesis ofS-Adenosyl-(L)-methionine, is catalyzed by the Methionine adenosyltransferase I,alpha ( MAT1A ) [1], [2], [3] and Methionineadenosyltransferase II, alpha ( MAT2A ) [4], [2], [5], [3], [6].
S-Adenosyl-(L)-methionine (AdoMet) is the primary methyl group donor invirtually all mammalian systems. DNA (cytosine-5-)-methyltransferase 1 ( D nmt 1 )[7], [8], DNA (cytosine-5-)-methyltransferase 3 alpha (DNMT3A ) [9] and DNA (cytosine-5-)-methyltransferase 3 beta (DNMT3B ) [9] naturally catalyze the transfer of the activated methylgroup from AdoMet to C5 atom of DNA cytosine with formation ofS-Adenosyl-(L)-homocysteine ( AdoHcy ).
S-adenosylhomocysteine hydrolase ( SAHH ) [10], [11],[12], S-adenosylhomocysteine hydrolase-like 1 ( SAHH2 ) [13] and S-Adenosylhomocysteine hydrolase-like 2 ( SAHH3 ) [13]catalyze the hydrolysis of AdoHcy to adenosine and (L)-Homocysteine. In turn,Cystathionine beta-synthase ( CBS ) catalyzes the condensation of(L)-Serine and (L)-Homocysteine to form (L)-Cystathionine [14], [15]. Cystathionase (cystathionine gamma-lyase) ( CTH )catalyzes the second step in the reverse trans-sulfuration pathway (the cleavage of the(L)-Cystathionine C-gamma-S bond) yielding (L)-Cysteine, 2-Oxobutanoicacid, and ammonia [16].
(L)-Methionine, as another amino acid involved in protein biosynthesis, thatforms aminoacyl-tRNA conjugated with corresponding tRNA by Methionyl-tRNA synthetase (MARS) [17], [18]. Mitochondrial (L)-Methionine*(tRNA)then undergoes formylation to N-Formyl-(L)-methionine*(tRNA) by Mitochondrialmethionyl-tRNA formyltransferase ( FMT) [19].
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