Abstract
1. The effect of folic acid and SH-glutathione on histidine de-aminase of the rabbit, which was reported in the previous papers, was reconfirmed (1). In this report Co_??_ was found to be another essential supplement.
2. When EDTA was added in the process of enzyme purification, the activity of the purified enzyme was no longer restored by Co_??_, Mn_??_, Zn_??_ or Cd_??_, but with addition of folic acid, SH-glutathione and Co_??_, the inactive enzyme regained its activity. The activation of Mn_??_, Zn_??_ and Cd_??_ was discussed.
3. From one molecule histidine, one molecule ammonia was produced by the thus activated enzyme and as the metabolite urocanic acid was proved by means of paperchromatography.
4. Folinic acid was found not to have such a restoring effect on histidine deaminase.
5. The disaccordance between Kato et al. (12) and the authors was discussed and it became clear, that this was to be attributed to the difference of the experimental animals.
