Quantum Yields for Enzyme Inactivation and the Amino Acid Composition of Proteins*

Summary A formula has been derived which as a first approximation, predicts the quantum yields for the inactivation of enzymes. The enzymes can be divided into a group containing cystine and the subtilisins which do not. The formula applied to subtilisin gives good agreement. For some of the enzymes, only cystine needs to be considered in the calculation; for others good agreement is found if contributions from aromatic groups are included. On this basis a quantum yield for tobacco mosaic virus protein is computed as 0.0047 at 2537 Å. The origin of chemically modified histidine in photochemically inactivated lysozyme has yet to be explained.