title: Methenyl-tetrahydromethanopterin cyclohydrolase in cell extracts of Methanobacterium.
abstract: Cell extracts of Methanobacterium thermoautotrophicum possess a methenyl-tetrahydromethanopterin (methenyl-H4MPT) cyclohydrolase. The enzyme catalyzes the hydrolysis of methenyl-H4MPT to formyltetrahydromethanopterin (formyl-H4MPT). The reaction is reversible and both the rate and extent of the reaction depend on the pH and the buffer used. Similarly, the nonenzymatic hydrolysis of methenyl-H4MPT is highly dependent on pH and buffer. An active derivative of methenyl-H4MPT was obtained in 94% yield by reacting H4MPT with formic acid in the presence of excess acetic acid under anoxic conditions at 80 degrees C for 3 h. H NMR spectroscopy and fast atom bombardment mass spectrometry revealed the product to be a derivative of methenyl-H4MPT which had lost the alpha-hydroxyglutarylphosphate unit. In spite of this loss, this derivative served both as a substrate for methanogenesis and for the cyclohydrolase. Comparison of the properties of the products of the enzymatic and nonenzymatic hydrolyses indicates that the enzymatic reaction yields N5-formyl-H4MPT whereas the nonenzymatic reaction yields N10-formyl-H4MPT.
mesh_terms: D000619:Aminohydrolases / Q000378:metabolism*; D019605:Euryarchaeota / Q000201:enzymology*; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D045064:Methenyltetrahydrofolate Cyclohydrolase; D013056:Spectrophotometry, Ultraviolet
chemical_list: D000619:Aminohydrolases; D045064:Methenyltetrahydrofolate Cyclohydrolase