Catalysis of the reaction: 2,3-diketo-5-methylthiopentyl-1-phosphate = H+ + 2-hydroxy 3-keto-5-methylthiopentenyl-1-phosphate. 2,3-diketo-5-methylthiopentyl-1-phosphate is also known as DK-MTP-1-P, and 2-hydroxy 3-keto-5-methylthiopentenyl-1-phosphate as HK-MTPenyl-1-P.
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