Methionine synthesis from 5'-S-Methylthioadenosine. Resolution of enzyme activities and identification of 1-phospho-5-S methylthioribulose.
5'-S-Methylthioadenosine is converted to methionine in mammalian systems, microorganisms and plants. 5'-S-Methylthioadenosine is first converted to 1-phospho-5-S-methylthioribofuranoside (1-PMTR) which is then converted to 2-keto-4-S-methylthiobutyrate, the precursor of methionine. We have now investigated the conversion of 1-PMTR to the keto acid. This conversion requires at least three protein fractions designated A, B, and C. Fraction A catalyzes an isomerization of 1-PMTR to form 1-phospho-5-S-methylthioribulose. The identification of this compound is based in part on the products obtained after NaIO4 oxidation, i.e. S-methylthioacetaldehyde, formate, and phosphoglycolic acid. When fractions A and B are added to 1-PMTR, two additional compounds, designated II and III, were detected. No O2 was consumed in the formation of compounds II and III. These compounds are, therefore, at the oxidation state of 5-S-methylthioribose. Compound II is phosphorylated as evidenced by its electrophoretic behavior before and after alkaline phosphatase treatment. Addition of fraction C to compounds II and III leads to O2 consumption and to the conversion of these compounds to 2-keto-4-S-methylthiobutyrate. Thus, compounds II and III are precursors of the keto acid. These compounds have not been fully characterized.
D000241:Adenosine / Q000031:analogs & derivatives* / Q000378:metabolism; D000818:Animals; D002855:Chromatography, Thin Layer; D003839:Deoxyadenosines; D008099:Liver / Q000201:enzymology*; D008297:Male; D008715:Methionine / Q000096:biosynthesis*; D010101:Oxygen Consumption; D010428:Pentosephosphates / Q000378:metabolism*; D010766:Phosphorylation; D051381:Rats; D011919:Rats, Inbred Strains; D012267:Ribosemonophosphates / Q000378:metabolism*; D012274:Ribulosephosphates / Q000378:metabolism*; D013865:Thioglycosides / Q000378:metabolism*; D013872:Thionucleosides / Q000378:metabolism*
C023029:5'-methylthioribose 1-phosphate; D003839:Deoxyadenosines; D010428:Pentosephosphates; D012267:Ribosemonophosphates; D012274:Ribulosephosphates; D013865:Thioglycosides; D013872:Thionucleosides; C008500:5'-methylthioadenosine; C038238:1-phospho-5-S-methylthioribulose; D008715:Methionine; D000241:Adenosine