The specificity of the dehydrases

SINCE Thunberg [1920] showed by means of the methylene blue technique that tissues could oxidise a variety of substances, there has been a question as to the specificity of the systems involved. It seemed unnecessarily complicated to assume a separate enzyme for each acid oxidised. Yet a high degree of specificity is the characteristic of most enzymes, and it is therefore unjustified, until definite proof is available, to assume that one system is responsible for the oxidation of, say, citric and lactic acids. Thunberg believed that each substance oxidised had a specific enzyme, but this "is rather unconvincingly inferred from their unequal resistances to thermal changes"