A Photochemical Yield for the Inactivation of Crystalline Trypsin

That enzymes can be inactivated by exposure to ultraviolet light has been demonstrated qualitatively by a number of investigators (l), but very few experiments have been conducted under conditions which permitted a calculation of the number of molecules inactivated per quantum of radiation absorbed. Obviously data of the latter type can be secured only for pure enzymes whose molecular weight is known. Quantum yields (molecules inactivated per quantum absorbed) as a function of wave-length for the inactivation of crystalline urease have been determined by Landen ((2), cf. (3)), and yields for pepsin can be calculated from the data of Gates ((4), cf. (2)). The very low yields (around 0.001) obtained for urease and pepsin did not permit any definite conclusions regarding the structure of these two protein molecules or the mechanism of their photochemical inactivation. With the hope of securing more detailed information under varied experimental conditions, and possibly higher quantum yields, it was considered desirable to extend this type of investigation to other enzymes. Trypsin has been selected for this purpose because it was known to consist of a single molecular species and because several synthetic substrates for it had been prepared by Bergmann and his coworkers (5). The present paper reports the absorption spectrum of crystalline trypsin as well as quantum yields for its inactivation at X 2537 and 2804 8. ; the yields are based on its loss of ability to release COOH groups in ar-benzoyl-Z-arginineamide hydrochloride.