Dietary creatine intake lowers creatine biosynthesis in rodents by inhibiting synthesis of guanidinoacetate
(GAA), the precursor of creatine, thereby sparing methyl groups and lowering total homocysteine (tHcys) (Guthmiller et al.
Increased GAA, increased GAA/crn ratio, and decreased CRE/ GAA ratio are informative markers of guanidinoacetate
methyltransferase (GAMT) deficiency.
It is well known that the transfer of the amidino group of arginine to glycine to yield L-ornithine and guanidinoacetate
(GM), which is catalyzed by L-arginine:glycine amidinotransferase, represents the first of two steps in the biosynthesis of Cr.
amidinotransferase (AGAT) and guanidinoacetate
methyltransferase activity in growing male rats fed on a raw field bean (Vicia faba L.
In a second reaction, catalyzed by guanidinoacetate
is methylated by S-adenosylmethionine to form S-adenosylhomocysteine and creatine (BLOCH; SCHOENHEIMER, 1941; BORSOOK; DUBNOFF, 1945).
Inicialmente, arginina e glicina combinam para formar guanidinoacetate
e, em seguida, um grupo de S-metil adenosilmetionina e acrescentado para a formacao de creatina.
Creatine is synthesized when the amino acid S-adenosylmethionine (SAM) methylates guanidinoacetate
to form creatine and S-adenosylhomocysteine.
Spencer has a guanidinoacetate
methyltransferase deficiency, which means his muscles do not work properly and he needs to be fed through a tube.
It is noteworthy that the formation of creatinine from methylation of guanidinoacetate
accounts for approximately 75% of all folate-dependent transmethylation reactions (Barr et al.
Improving treatment of guanidinoacetate
methyltransferase deficiency: reduction of guanidinoacetic acid in body fluids by arginine restriction and ornithine supplementation.
The formation of creatine from methylation of guanidinoacetate
has been estimated to account for approximately 75% of transmethylation reactions (Mudd and Poole 1975).