Kinetic specificity in papain-catalysed hydrolyses.
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ABSTRACT:
SUBMITTER: Lowe G
PROVIDER: S-EPMC1177119 | biostudies-other | 1971 Aug
REPOSITORIES: biostudies-other
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Project description:1. The self-catalysed hydrolyses of the thiol esters, S-hippurylthioglycollic acid and S-ethyl monothiolsuccinate, have been shown to be slower than the deacylation step for the papain-catalysed hydrolysis of hippuric esters, by a factor approx. 10(5). This difference in rate constants largely reflects a difference in activation energy, which together with other evidence drawn from the literature make it unlikely that a carboxylate ion could be the nucleophile responsible for the deacylation of acyl-papain. 2. The imidazole-catalysed hydrolysis of S-hippurylthioglycollic acid and ethyl thiolacetate have activation energies similar to that for the deacylation step in papain-catalysed hydrolyses. This, together with other evidence drawn from the literature, suggests that the imidazole of a histidine residue is the nucleophile responsible for the deacylation of acyl-papain.
| S-EPMC1206921 | biostudies-other
Project description:1. The maximum rate of production of p-nitrophenol (V(max.)) for both papain- and ficin-catalysed hydrolyses of p-nitrophenyl hippurate is independent of methanol concentration up to 2m for papain and 1.5m for ficin. 2. The observed catalytic constant (k(0)) for the production of hippuric acid for both papain- and ficin-catalysed hydrolyses of methyl hippurate decreases with increasing methanol concentration, 1/k(0) being linearly dependent on the methanol concentration. The k(MeOH)/k(H2O) ratio is determined. 3. These results provide strong evidence against general base catalysis for the rate-determining step in the deacylation of hippuryl-papain and hippuryl-ficin and probably for other specific acyl-papains and acyl-ficins. 4. The rate-determining step for the deacylation of the non-specific trans-cinnamoyl-papain appears to be different from that for the specific hippuryl-papain, and is probably subject to general base catalysis. It is possible, however, to accommodate all these observations in a single four-step reaction pathway. 5. Propan-2-ol did not influence the rate of production of hippuric acid for the papain-catalysed hydrolysis of methyl hippurate. A similar result has previously been reported for the ficin-catalysed hydrolysis of methyl hippurate. Ethanol and of course methanol (see 2) decrease the rate of production of hippuric acid for both papain- and ficin-catalysed hydrolyses of methyl hippurate. It is suggested that the secondary alcohol is incapable for structural reasons of approaching the bond to be hydrolysed.
| S-EPMC1270121 | biostudies-other
Project description:1. Methyl thionohippurate was prepared and shown to be a specific substrate for both papain and ficin. 2. The ultraviolet-absorption properties of the acyl-enzyme intermediate for both papain and ficin with methyl thionohippurate was that expected of an acyl-thiol. The possibility that other functional groups present in papain or ficin might be the site of acylation has been excluded. 3. The change in extinction at the absorption maximum with time was as expected for the acyl-enzyme on the basis of the known Michaelis-Menten parameters for methyl thionohippurate. 4. The variation of extinction with initial substrate concentration for both papain and ficin was that expected from the Michaelis-Menten parameters. 5. The extinction of the absorption maximum of the thionohippuryl-enzyme intermediate was suppressed by the addition of methyl hippurate to the extent predicted from the Michaelis-Menten parameters. 6. The decay of the extinction for the acyl-enzyme was arrested by adjusting the pH of the solution to 2.5. 7. These experiments provide compelling evidence that the acylation by substrate of both papain and ficin takes place through a thiol residue.
| S-EPMC1206920 | biostudies-other
Project description:1. Three synthetic substrates of cathepsin B (EC 3.4.22.1) with various amino acid residues at the P2 position (Cbz-Phe-Arg-NH-Mec, Cbz-Arg-Arg-NH-Mec and Cbz-Cit-Arg-NH-Mec, where Cbz represents benzyloxycarbonyl and NH-Mec represents 4-methylcoumarin-7-ylamide) were used to investigate the pH-dependency of cathepsin B-catalysed hydrolyses and to obtain information on the nature of enzyme-substrate interactions. 2. Non-linear-regression analysis of pH-activity profiles for these substrates indicates that at least four ionizable groups on cathepsin B with pKa values of 3.3, 4.55, 5.46 and greater than 7.3 can affect the rate of substrate hydrolysis. 3. Ionization of the residue with a pKa of 5.46 has a strong effect on activity towards the substrate with an arginine in P2 (8.4-fold increase in activity) but has only a moderate effect on the rate of hydrolysis with Cbz-Cit-Arg-NH-Mec (2.3-fold increase in activity) and virtually no effect with Cbz-Phe-Arg-NH-Mec. The kinetic data are consistent with this group being an acid residue with a side chain able to interact with the side chains of an arginine or a citrulline in the P2 position of a substrate. Amino acid sequence alignment and model building with the related enzyme papain (EC 3.4.22.2) suggest that Glu-245 of cathepsin B is a likely candidate. The relative importance of electrostatic and hydrophobic interactions in the S2 subsite of cathepsin B is discussed. 4. For all three substrates, activity appears after ionization of a group with a pKa of 3.3, believed to be the active-site Cys-29 of cathepsin B. The identity of the groups with pKa values of 4.55 and greater than 7.3 remains unknown.
| S-EPMC1150117 | biostudies-other
Project description:1. The hydrolyses of the p-nitrophenyl esters of N-benzyloxycarbonylglycine, alpha-N-benzyloxycarbonyl-L-lysine and N-methoxycarbonyl-L-phenylalanylglycine catalysed by papain (EC 3.4.22.2) have been studied in solvents having a variable composition of 2H2O and H2O. 2. kcat., which represents deacylation in the papain-catalysed hydrolysis of reactive esters, is some 2.3-fold less in 2H2O compared with H2O. The magnitude of kcat. has been determined as a function of the 2H atom fraction of the solvent. 3. Both linear and non-linear methods of least-square regression analysis have been applied to the data in order to obtain best-fit parameter values for several three-parameter models which express kcat. in terms of the 2H atom fraction of the solvent. These models represent some possible modes of restructuring of the active site protonic configuration consequent upon transition state formation. 4. The results of curve fitting reveal an essentially linear dependence of kcat. upon the 2H atom fraction, and it may therefore be concluded that the isotope effect originates from a single proton which is in the process of transfer in the transition state. 5. It is postulated on the basis of this and other evidence that the mobile proton is transferred from an attacking water molecule to the imidazole side chain of His-159 during tetrahedral intermediate formation. This has the effect of stabilizing the transition state and promoting catalysis. The role of His-159 in deacylation is therefore to provide general base catalysis. 6. Models that involve two or more protons, such as a two-proton relay system analogous to that proposed for the serine proteinases, or a multiproton 'medium' effect, are considered unlikely on the basis of the data reported in this paper. 7. A more detailed examination of possible transition state structures reveals that the only structure compatible with available experimental data and consistent with certain theoretical predictions is one in which the proton translocated in concern with reorganization of the heavy atom framework. In addition, the transition state vibrations of the mobile proton are strongly coupled to those of the heavy atoms. These properties of the transition state are also manifest in the transition state for the deacylation of serine proteinases.
| S-EPMC1163425 | biostudies-other
Project description:1. The Michaelis-Menten parameters for the papain-catalysed hydrolysis of a number of alkyl, aryl and alkyl-thiol esters of hippuric acid have been determined. 2. For all the aryl esters and most of the alkyl esters studied, the catalytic constant, k(0), is 2-3sec.(-1) and most probably represents deacylation of the common intermediate, hippuryl-papain. 3. Two alkyl esters and hippurylamide, however, have catalytic rate constants, k(0), less than 2-3sec.(-1). It is possible to interpret all the available kinetic data in terms of a three-step mechanism in which an enzyme-substrate complex is first formed, followed by acylation of the enzyme through an essential thiol group, followed by deacylation of the acyl-enzyme. 4. The logarithm of the ratio of the Michaelis-Menten parameters, which reflect the acylation rate constant, for four aryl esters of hippuric acid studied give a linear Hammett plot against the substituent constant, sigma. Arguments are presented that indicate acid as well as nucleophilic catalysis in the acylation process and that the most likely proton donor is an imidazolium ion. 5. It is suggested that this imidazolium ion is part of the same histidine residue that has been tentatively implicated in the deacylation process (Lowe & Williams, 1965b). 6. A new mechanism is proposed for the papain-catalysed hydrolysis of N-acyl-alpha-amino acid derivatives.
| S-EPMC1206922 | biostudies-other
Project description:1. N-Benzoyl-l-serine methyl ester was synthesized and evaluated as a substrate for bromelain (EC 3.4.22.4) and for papain (EC 3.4.22.2). 2. For the bromelain-catalysed hydrolysis at pH7.0, plots of [S(0)]/v(i) (initial substrate concn./initial velocity) versus [S(0)] are markedly curved, concave downwards. 3. Analysis by lattice nomography of a modifier kinetic mechanism in which the modifier is substrate reveals that concave-down [S(0)]/v(i) versus [S(0)] plots can arise when the ratio of the rate constants that characterize the breakdown of the binary (ES) and ternary (SES) complexes is either less than or greater than 1. In the latter case, there are severe restrictions on the values that may be taken by the ratio of the dissociation constants of the productive and non-productive binary complexes. 4. Concave-down [S(0)]/v(i) versus [S(0)] plots cannot arise from compulsory substrate activation. 5. Computational methods, based on function minimization, for determination of the apparent parameters that characterize a non-compulsory substrate-activated catalysis are described. 6. In an attempt to interpret the catalysis by bromelain of the hydrolysis of N-benzoyl-l-serine methyl ester in terms of substrate activation, the general substrate-activation model was simplified to one in which only one binary ES complex (that which gives rise directly to products) can form. 7. In terms of this model, the bromelain-catalysed hydrolysis of N-benzoyl-l-serine methyl ester at pH7.0, I=0.1 and 25 degrees C is characterized by K(m) (1) (the dissociation constant of ES)=1.22+/-0.73mm, k (the rate constant for the breakdown of ES to E+products, P)=1.57x10(-2)+/-0.32x10(-2)s(-1), K(a) (2) (the dissociation constant that characterizes the breakdown of SES to ES and S)=0.38+/-0.06m, and k' (the rate constant for the breakdown of SES to E+P+S)=0.45+/-0.04s(-1). 8. These parameters are compared with those in the literature that characterize the bromelain-catalysed hydrolysis of alpha-N-benzoyl-l-arginine ethyl ester and of alpha-N-benzoyl-l-arginine amide; K(m) (1) and k for the serine ester hydrolysis are somewhat similar to K(m) and k(cat.) for the arginine amide hydrolysis and K(as) and k' for the serine ester hydrolysis are somewhat similar to K(m) and k(cat.) for the arginine ester hydrolysis. 9. A previous interpretation of the inter-relationships of the values of k(cat.) and K(m) for the bromelain-catalysed hydrolysis of the arginine ester and amide substrates is discussed critically and an alternative interpretation involving substantial non-productive binding of the arginine amide substrate to bromelain is suggested. 10. The parameters for the bromelain-catalysed hydrolysis of the serine ester substrate are tentatively interpreted in terms of non-productive binding in the binary complex and a decrease of this type of binding by ternary complex-formation. 11. The Michaelis parameters for the papain-catalysed hydrolysis of the serine ester substrate (K(m)=52+/-4mm, k(cat.)=2.80+/-0.1s(-1) at pH7.0, I=0.1, 25.0 degrees C) are similar to those for the papain-catalysed hydrolysis of methyl hippurate. 12. Urea and guanidine hydrochloride at concentrations of 1m have only small effects on the kinetic parameters for the hydrolysis of the serine ester substrate catalysed by bromelain and by papain.
| S-EPMC1168089 | biostudies-other
Project description:Arf (ADP-ribosylation factor) GAPs (GTPase-activating proteins) are enzymes that catalyse the hydrolysis of GTP bound to the small GTP-binding protein Arf. They have also been proposed to function as Arf effectors and oncogenes. We have set out to characterize the kinetics of the GAP-induced GTP hydrolysis using a truncated form of ASAP1 [Arf GAP with SH3 (Src homology 3) domain, ankyrin repeats and PH (pleckstrin homology) domains 1] as a model. We found that ASAP1 used Arf1-GTP as a substrate with a k(cat) of 57+/-5 s(-1) and a K(m) of 2.2+/-0.5 microM determined by steady-state kinetics and a kcat of 56+/-7 s(-1) determined by single-turnover kinetics. Tetrafluoroaluminate (AlF4-), which stabilizes complexes of other Ras family members with their cognate GAPs, also stabilized a complex of Arf1-GDP with ASAP1. As anticipated, mutation of Arg-497 to a lysine residue affected kcat to a much greater extent than K(m). Changing Trp-479, Iso-490, Arg-505, Leu-511 or Asp-512 was predicted, based on previous studies, to affect affinity for Arf1-GTP. Instead, these mutations primarily affected the k(cat). Mutants that lacked activity in vitro similarly lacked activity in an in vivo assay of ASAP1 function, the inhibition of dorsal ruffle formation. Our results support the conclusion that the Arf GAP ASAP1 functions in binary complex with Arf1-GTP to induce a transition state towards GTP hydrolysis. The results have led us to speculate that Arf1-GTP-ASAP1 undergoes a significant conformational change when transitioning from the ground to catalytically active state. The ramifications for the putative effector function of ASAP1 are discussed.
| S-EPMC1863566 | biostudies-literature
Project description:The specificity of the S(1)' subsite of the proteolytic enzyme papain was investigated by studying the effect of l-alpha-amino acid amides on the enzyme-catalysed hydrolysis of N-benzyloxycarbonylglycine p-nitrophenyl ester and by determining the kinetic parameters for the enzyme-catalysed hydrolysis of some N-benzyloxycarbonylglycyl-l-amino acid amides. These studies showed that the S(1)' subsite has a predilection for hydrophobic residues, in particular l-leucine and l-tryptophan. The specificity for these residues is manifest in both the binding and acylation steps. N-Benzyloxycarbonylglycine amide is not hydrolysed under comparable conditions, indicating that the amide group adjacent to and on the C-terminal side of the peptide bond about to be cleaved makes an important contribution to the rate of the papain-catalysed hydrolysis of peptides.
| S-EPMC1168104 | biostudies-other
Project description:Optically active 1,2-diols are valuable buildings blocks in organic synthesis. In the present paper, a set of racemic 1,2-diols with an ester functional group are prepared, starting from ?-ketoesters in a three-step procedure with moderate yields. The racemic 1,2-diols, containing a chiral quaternary center in their structure, are subjected to selective acylation in order to perform their kinetic resolution catalysed by a set of commercially available lipases. Under optimized reaction conditions, good conversions and enantioselectivities are achieved by using the lipase PSL-C from Pseudomonas cepacia in tert-butyl methyl ether. This biocatalyst could be reused up to five times without losing its properties.
| S-EPMC6100382 | biostudies-literature