INVESTIGATION OF SERINE HYDROXYMETHYLTRANSFERASE IN METHANOGENS

The cofactor specificity of serine hydroxymethyltransferase (SHMT) act ivities was tested in extracts of several methanogens using tetrahydro methanopterin (H4MPt) from Methanobacterium thermoautotrophicum Marbur g, tetrahydrosarcinapterin (H4SPt) from Methanosarcina barkeri, and te trahydrofolate (H(4)folate) as the potential C-1 carrier. In Methanosp haera stadtmanae and Methanococcus thermolithotrophicus, the activitie s were H4MPt dependent. In Methanospirillum hungatei GP1, Methanosaeta concilii, Methanolobus tindarius, and Methanosarcina barkeri Fusaro, the activities were strictly H(4)folate dependent. H2SPt was reactive with SHMT of Methaospirillum hungatei, pyridoxal phosphate stimulated SHMT activity. The apparent K-m values H(4)folate and L-serine were 0. 086 and 0.29 mM in Methanosarcina barkeri and 0.065 and 0.31 mM in Met hanospirillum hungatei, respectively.