5'-deoxyadenosine deaminase (also known as "DadD") is an enzyme that catalyzes the conversion of 5′-deoxyadenosine to 5′-deoxyinosine. To a lesser extent, the enzyme also catalyzes the deamination of 5′-methylthioadenosine, S-adenosylhomocysteine, and adenosine. The molecular mass of the DadD enzyme is approximately 230 kDa. DadD maintains 90% of its enzymatic activity after being heated at 60 degrees Celsius for ten minutes. The preferred pH for 5'deoxyadenosine deaminase is 9.0, with the enzyme denaturing at a pH of 11. The DadD enzyme has a preferred substrate of 5'deoxyadenosine, though it will also react with 5′-methylthioadenosine, S-adenosylhomocysteine, and adenosine at lower efficiencies.