Catalyzes the cleavage of 2-ketobutyrate to propionyl-CoA and formate. It can also use pyruvate as substrate. 2-oxobutanoate + CoA = formate + propanoyl-CoA acetyl-CoA + formate = CoA + pyruvate Dependent on PFL-activase. Amino-acid degradation; L-threonine degradation via propanoate pathway; propanoate from L-threonine: step 2/4. Strongly repressed by glucose. Anaerobic growth of the pfl mutant in the presence of cAMP and L-threonine induced synthesis of TdcE. No discernible phenotype. Belongs to the glycyl radical enzyme (GRE) family. PFL subfamily.