Denaturation o f proteins by urea has received a great deal of attention. Some of the earlier studies are cited in the paper by Steinhardt ('38) and in the general review of protein denaturation by Neurath et al. ( '44). The papers of Kanzmann et al. ('53) contain numerous references to more recent work.
Tn contrast with the relatively great amount of work involving the effects of urea upon proteins in general, its influence upon enzyme activity does not appear to have been very much studied, although the rate of an enzyme-catalyzed reaction would seem to be an excellent criterion. We have been able to find relatively few papers in whicli enzyme activity was utilized f o r study. Some examples are the experiments of Bhagvat et al. ('39) on amine oxidase, the work of Dentsch ( '51) utilizing crystalline horse erythrocyte catalase and Dzialoszynslii's ( '31) investigations with phcnolsulfatase.
The enzyme, luciferase, from the luminescent ostracod crustacean, Cypridifia hilgendorfii, lias been extensively studied in other connections (Harvey, '52).
While not yet crystallized, it has recently been considerably purified (McElrop and Chase, '51). The blue luminescence of the luciferaselnciferin reaction, which is an instantaneous measure o f its rate, can be determined with rather high precision by the This research was supported in part by funds of the Eugwe IIiggins Trust allocated to Princeton University.