title: 5'-Methylthioadenosine phosphorylase from Caldariella acidophila. Purification and properties.
abstract: The occurrence of 5'-methylthioadenosine phosphorylase in Caldariella acidophila, a thermophilic bacterium growing optimally at 87 degrees C, is reported. It represents the first example in prokaryotes of a phosphoryolytic cleavage of the thioether. The reaction products, purified by ion-exchange chromatography, have been identified as 5-methylthioribose-1-phosphate and adenine by several analytical procedures. The enzyme has been purified to homogeneity in 32% yield by using DEAE-cellulose and hydroxyapatite chromatography, gel filtration and isoelectric focusing. The enzyme shows a high degree of thermophilicity, its temperature optimum being at 93 degrees C; furthermore no loss of activity is observable after exposure for 1 h at 100 degrees C. The kinetic data indicate a sequential mechanism of the reaction. The apparent Km values are 0.095 mM for 5'-methylthioadenosine and 6.1 mM for phosphate. The specificity of the reaction is rather strict. Experiments performed with analogues of the substrate, i.e. 5'-methylthioinosine, 5'-dimethylthioadenosine sulfonium salt, 5'-n-butylthioadenosine, 5'-isobutylthioadenosine, 5'-isobutylthioinosine, adenosylhomocysteine, 5'-thioethanoladenosine, adenosine, indicate the relevance of the adenine amino group and the sulfur in thioether form in the binding to the enzyme protein.
mesh_terms: D000241:Adenosine / Q000031:analogs & derivatives; D001419:Bacteria / Q000201:enzymology*; D004355:Drug Stability; D006358:Hot Temperature; D007700:Kinetics; D010430:Pentosyltransferases / Q000378:metabolism*; D011683:Purine-Nucleoside Phosphorylase / Q000302:isolation & purification / Q000378:metabolism*; D013379:Substrate Specificity; D013872:Thionucleosides
chemical_list: D013872:Thionucleosides; D010430:Pentosyltransferases; D011683:Purine-Nucleoside Phosphorylase; C021784:5'-methylthioadenosine phosphorylase; D000241:Adenosine