SHM1 (YBR263W, P37292) notes

• Mitochondrial serine hydroxymethyltransferase (EC 2.1.2.1), PLP, transit peptide 1-20 [UniProt:P37292 "SUBCELLULAR LOCATION: Mitochondrion."].
• Isozyme assignment by sequence and fractionation PMID:8132653.
• Classical tmp3 (= shm1) mutant: lost one SHMT form, partial loss of activity, multiple one-carbon auxotrophies [PMID:1100397 "Crude extracts of this mutant present a 60% decrease of serine transhydroxymethylase specific activity as compared to a wild-type strain"; PMID:6271 title "Two forms of serine transhydroxymethylase, one absent in a thymidylate-less mutant"].
• Direction depends on nutrition; Shm1 makes serine from glycine when glycine is the one-carbon source, and contributes one-carbon units but not glycine for purines [PMID:9398220 "When grown on glycine, the mitochondrial SHMT was the predominant isozyme catalyzing the synthesis of serine from glycine and one-carbon units"; "the mitochondrial SHMT made a significant contribution of one-carbon units, but not glycine, for purine synthesis"].
• Only ~5% of total SHMT activity is mitochondrial PMID:9398220.
• YeastPathways RCA rows place SHM1 reactions in the cytosol and in superpathways (chorismate, folate polyglutamylation); these are not supported for the mitochondrial isozyme.