Substrate specificity of methylthioadenosine phosphorylase from human liver

Methylthioadenosine (MTA) phosphorylase purified 615-fold from human liver cleaved phosphorolytically nucleoside analogues at the decreasing specific activity: 5'-deoxyadenosine > 5'-iodo-5'-deoxyadenosine > MTA > adenosine > 2-chloro- adenosine > 2-chloro-5'-0-methyl-2'-deoxyadenosine > 2-chloro-2'-deoxyadenosine > > 2'-deoxyadenosine. Adenosine and analogues of 5'-deoxyadenosine were strong competitive inhibitors of MTA phosphorolysis catalysed by the human liver enzyme.