Catalyzes the deamination of three SAM-derived enzymatic products, namely 5'-deoxyadenosine, S-adenosyl-L-homocysteine, and 5'-methylthioadenosine, to produce the inosine analogs. Can also deaminate adenosine. The preferred substrate for this enzyme is 5'-deoxyadenosine, but all these substrates are efficiently deaminated (PubMed:24375099). Likely functions in a S-adenosyl-L-methionine (SAM) recycling pathway from S-adenosyl-L-homocysteine (SAH) produced from SAM-dependent methylation reactions (PubMed:25917907). May also be involved in the recycling of 5'-deoxyadenosine, whereupon the 5'-deoxyribose moiety of 5'-deoxyinosine is further metabolized to deoxyhexoses used for the biosynthesis of aromatic amino acids in methanogens (PubMed:24375099). 5'-deoxyadenosine + H(+) + H2O = 5'-deoxyinosine + NH4(+) H(+) + H2O + S-adenosyl-L-homocysteine = NH4(+) + S-inosyl-L-homocysteine H(+) + H2O + S-methyl-5'-thioadenosine = NH4(+) + S-methyl-5'-thioinosine adenosine + H(+) + H2O = inosine + NH4(+) Binds 1 zinc ion per subunit. kcat is 120000 sec(-1) for 5'-deoxyadenosine deamination. kcat is 160 sec(-1) for S-methyl-5'-thioadenosine deamination. kcat is 1300 sec(-1) for S-adenosyl-L-homocysteine deamination. kcat is 110 sec(-1) for adenosine deamination (at pH 9 and 60 degrees Celsius). Optimum pH is 9.0. Amino-acid biosynthesis; S-adenosyl-L-methionine biosynthesis. Homotetramer. SAH is a product of SAM methyltransferases and is known to be a feedback inhibitor of these enzymes. As a result of this inhibition, organisms have evolved efficient enzymes to metabolize SAH via different pathways. The pathway found in methanogens differs from the canonical pathway, it uses the deamination of S-adenosyl-L-homocysteine to form S-inosyl-L-homocysteine for the regeneration of SAM from S-adenosyl-L-homocysteine (PubMed:25917907). 5'-deoxyadenosine is a radical SAM enzyme reaction product which strongly inhibits radical SAM enzymes. A pathway for removing this product must be present in methanogens where the MTA/SAH nucleosidase which normally metabolizes this compound is absent (PubMed:24375099). Belongs to the metallo-dependent hydrolases superfamily. MTA/SAH deaminase family.