. 2020 Apr 21;25(8):1933. doi: 10.3390/molecules25081933

Table 2.

Examples of inverse solvent isotope effects due to cysteine thiols.

Enzyme	Varied Substrate/Agent	Inverse SKIE ¹	Reference
papain	Bz-Gly-OPh	^D2Ok_ac = 0.63	[14]
	Bz-Arg-NH₂	^D2Ok_ac = 0.58	[14]
	Bz-Cit-NH₂	^D2Ok_ac = 0.46	[14]
	Z-Phe-Gly-NH₂	^D2Ok_ac = 0.63	[14]
	bromoacetamide	^D2Ok_alk = 0.74	[14]
cysteine (papain model)	bromoacetate	^D2Ok_alk = 0.70 ± 0.02	[15]
	chloroacetate	^D2Ok_alk = 0.85 ± 0.10	[15]
	bromoacetamide	^D2Ok_alk = 0.69 ± 0.10	[15]
	chloroacetamide	^D2Ok_alk = 0.64 ± 0.04	[15]
	methyl bromoacetate	^D2Ok_alk = 0.53 ± 0.03	[15]
cathepsin C	Ser-Tyr-AMC	^D2O(k_cat/K_m) = 0.71 ± 0.14	[9]
protein arginine deiminase	Bz-Arg-OEt (PAD2)	^D2O(k_cat/K_m) = 0.8 ± 0.1	[16]
protein arginine deiminase	Bz-Arg-OEt (PAD4)	^D2O(k_cat/K_m) = 0.43	[17]
isocitrate lyase	succinate	^D2O(k_cat/K_m) = 0.56 ± 0.07	[10]
adenosine deaminase	adenosine 7,8-dihydro-8-oxoadenosine	^D2O(k_cat/K_m) = 0.77 ± 0.06	[18]
adenosine deaminase	adenosine 7,8-dihydro-8-oxoadenosine	^D2O(k_cat/K_m) = 0.45 ± 0.04	[18]

¹k_ac = the rate constant for enzyme acylation; k_alk = the rate constant for enzyme alkylation.