1. Some 16 amino acids (not containing SH or S-S groups) did not affect the reactivation of yeast invertase inactivated by acid.
2. Cysteine, reduced glutathione, homocysteine, thiophenol, and thioglycollic acid accelerated the reactivation of yeast invertase.
3. Cystine, oxidized glutathione, and homocystine inhibited the reactivation of yeast invertase.
4. The compounds mentioned in 2 and 3 did not affect native invertase.
5. The use of compounds in which the H of the SH group of homocysteine was substituted by a methyl or benzyl nullified the accelerative effect.
6. The longer the cysteine remained in contact with the inactivating enzyme, the greater was the velocity of the reactivated invertase.
7. The per cent acceleration by cysteine is inversely proportional to the control rate.
