Solvent isotope effects on tautomerization equilibria of papain and model thiolamines

Creighton, Donald J.; Schamp, David J.

doi:10.1016/0014-5793(80)80100-1

Cited by 21 publications

(30 citation statements)

References 13 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…These magnitudes agree with those measured for non-enzymatic models of thiolate alkylation by α-haloacetic acid derivatives using cysteine (0.53-0.85) [15]. These inverse effects agree with the SEIE on thiol deprotonation by an amine (φ RSL = 0.43) [19].…”

Section: Cysteine Proteases: Papain and Cathepsin Csupporting

confidence: 83%

Inverse Solvent Isotope Effects in Enzyme-Catalyzed Reactions

Fernandez

Murkin

2020

Molecules

View full text Add to dashboard Cite

Solvent isotope effects have long been used as a mechanistic tool for determining enzyme mechanisms. Most commonly, macroscopic rate constants such as k cat and k cat /K m are found to decrease when the reaction is performed in D 2 O for a variety of reasons including the transfer of protons. Under certain circumstances, these constants are found to increase, in what is termed an inverse solvent kinetic isotope effect (SKIE), which can be a diagnostic mechanistic feature. Generally, these phenomena can be attributed to an inverse solvent equilibrium isotope effect on a rapid equilibrium preceding the rate-limiting step(s). This review surveys inverse SKIEs in enzyme-catalyzed reactions by assessing their underlying origins in common mechanistic themes. Case studies for each category are presented, and the mechanistic implications are put into context. It is hoped that readers may find the illustrative examples valuable in planning and interpreting solvent isotope effect experiments.

show abstract

Section: Cysteine Proteases: Papain and Cathepsin Csupporting

confidence: 83%

Inverse Solvent Isotope Effects in Enzyme-Catalyzed Reactions

Fernandez

Murkin

2020

Molecules

View full text Add to dashboard Cite

show abstract

“…measurements in the case of thiolsubtilisin (Jordan & Polgar, 1981) that has a similar mercaptide-imidazolium ion-pair (Polgar, 1974a). Ionpair formation in papain is also supported by other recent data, such as potentiometric difference titration (Lewis et al, 1976), alkylations with negatively charged reactants (Halasz & Polgar, 1977), and kinetic deuterium isotope effects (Polgar, 1979;Creighton & Schamp, 1980;Frankfater & Kuppy, 1981). A closely similar ion-pair is also present in ficin as indicated by alkylations with chloroacetate (Brocklehurst et al, 1982).…”

Section: The Cysteine-histidine Couplesupporting

confidence: 74%

Current problems in mechanistic studies of serine and cysteine proteinases

Polgár¹,

Halász²

1982

Biochemical Journal

165

View full text Add to dashboard Cite

“…Thus, the isotope effect on kybs should only reflect Scheme 2 the intrinsic isotope effect on the rate of alkylation controlled by an inverse isotope effect on the tautoof the mercaptide ion containing form, 2. This isotope merization equilibrium constant, which in Hz0 is -2 effect is anticipated to be near unity since no apparent as first suggested in [3,4]. On the other hand, the proton transfers are involved in the alkylation of 2.…”

Section: Resultsmentioning

confidence: 58%

“…This range encompasses a predicted isotope effect of -0.8 calculated from eq. (4) under conditions where k, 9 k3, kr/kf z 1 and given that K$ =Z 2 and KF2 N 5, as estimated from the spectrophotometric titration of cysteine in Hz0 and D20 [4]. For /3-mercaptoethylamine an inverse isotope effect on kybs is not expected since 2 predominates over 3_ such that K3s % 1 f4].…”

Section: Resultsmentioning

confidence: 99%

“…The possibility has been suggested that observed inverse kinetic isotope effects could arise from preferential reaction of these alkylating agents with the proposed active site thiolate-imidazolium ion pair, formed between the active site sulfhydryl group and a neighboring imidazole function, provided that the tautomerization equilibrium constant (K) controlling the relative concentrations of ion pair (II) and its tautomer (I) is -2 in HzO, eq. (1) [4]:…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation