S-methyl-5-thio-D-ribulose 1-phosphate = 5-methylsulfanyl-2,3-dioxopentyl phosphate + H2O 5-methylsulfanyl-2,3-dioxopentyl phosphate + H2O = 1,2-dihydroxy-5-(methylsulfanyl)pent-1-en-3-one + phosphate Binds 1 zinc ion per subunit. Binds 1 Mg(2+) ion per subunit. Amino-acid biosynthesis; L-methionine biosynthesis via salvage pathway; L-methionine from S-methyl-5-thio-alpha-D-ribose 1-phosphate: step 2/6. Amino-acid biosynthesis; L-methionine biosynthesis via salvage pathway; L-methionine from S-methyl-5-thio-alpha-D-ribose 1-phosphate: step 3/6. Amino-acid biosynthesis; L-methionine biosynthesis via salvage pathway; L-methionine from S-methyl-5-thio-alpha-D-ribose 1-phosphate: step 4/6. In the N-terminal section; belongs to the aldolase class II family. MtnB subfamily. In the C-terminal section; belongs to the HAD-like hydrolase superfamily. MasA/MtnC family.