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J. Bacteriol., Dec 1997, 7456-7461, Vol 179, No. 23
S Delle Fratte, RH White, B Maras, F Bossa and V Schirch
Serine hydroxymethyltransferase (SHMT) catalyzes the reversible cleavage of
serine to glycine with the transfer of the one-carbon group to
tetrahydrofolate to form 5,10-methylenetetrahydrofolate. No SHMT has been
purified from a nonmethanogenic Archaea strain, in part because this group
of organisms uses modified folates as the one-carbon acceptor. These
modified folates are not readily available for use in assays for SHMT
activity. This report describes the purification and characterization of
SHMT from the thermophilic organism Sulfolobus solfataricus. The exchange
of the alpha-proton of glycine with solvent protons in the absence of the
modified folate was used as the activity assay. The purified protein
catalyzes the synthesis of serine from glycine and a synthetic derivative
of a fragment of the natural modified folate found in S. solfataricus.
Replacement of the modified folate with tetrahydrofolate did not support
serine synthesis. In addition, this SHMT also catalyzed the cleavage of
both allo-threonine and beta-phenylserine in the absence of the modified
folate. The cleavage of these two amino acids in the absence of
tetrahydrofolate is a property of other characterized SHMTs. The enzyme
contains covalently bound pyridoxal phosphate. Sequences of three peptides
showed significant similarity with those of peptides of SHMTs from two
methanogens.
Copyright © 1997, American Society for Microbiology
Purification and properties of serine hydroxymethyltransferase from Sulfolobus solfataricus
Department of Biochemistry and Molecular Biophysics, Virginia Commonwealth University, Richmond 23298, USA.
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