The photoinactivation of taka-amylase A, in the absence and presence of sensitizer, riboflavin, is due to the photooxidation of amino acid residues, cystine, tryptophan, tyrosine and histidine. The process of ejection of photoelectron from triplet state via excited singlet state is important for the ultraviolet inactivation. The stablilization of triplet state of riboflavin is essentially important process for the riboflavin-sensitized photoinactivation of taka-amylase A. These processes can be controlled by the spin-orbital coupling effect in the presence of paramagnetic ions. The formation of enzyme-substrate and -product complexes protects enzyme from ultraviolet and visible inactivation.