Mapping the active sites of bovine thrombin, factor IXa, factor Xa, factor XIa, factor XIIa, plasma kallikrein, and trypsin with amino acid and peptide thioesters: development of new sensitive substrates

Effects of secondary interactions on the kinetics of peptide and peptide ester hydrolysis by tissue kallikrein and trypsin

Kinetic constants for the hydrolysis by porcine tissue beta-kallikrein B and by bovine trypsin of a number of peptides related to the sequence of kininogen (also one containing a P2 glycine residue instead of phenylalanine) and of a series of corresponding arginyl peptide esters with various apolar P2 residues have been determined under strictly comparative conditions. kcat and kcat/Km values for the hydrolysis of the Arg-Ser bonds of the peptides by trypsin are conspicuously high. kcat for the best of the peptide substrates, Ac-Phe-Arg-Ser-Val-NH2, even reaches kcat for the corresponding methyl ester, indicating rate-limiting deacylation also in the hydrolysis of a peptide bond by this enzyme. kcat/Km for the hydrolysis of the peptide esters with different nonpolar L-amino acids in P2 is remarkably constant (range 1.7), as it is for the pair of the above pentapeptides with P2 glycine or phenylalanine. kcat for the ester substrates varies fivefold, however, being greatest for the P2 glycine compounds. Obviously, an increased potential of a P2 residue for interactions with the enzyme lowers the rate of deacylation. In contrast to results obtained with chymotrypsin and pancreatic elastase, trypsin is well able to tolerate a P3 proline residue. In the hydrolysis of peptide esters, tissue kallikrein is definitely superior to trypsin. Conversely, peptide bonds are hydrolyzed less efficiently by tissue kallikrein and the acylation reaction is rate-limiting. The influence of the length of peptide substrates is similar in both enzymes and indicates an extension of the substrate recognition site from subsite S3 to at least S'3 of tissue kallikrein and the importance of a hydrogen bond between the P3 carbonyl group and Gly-216 of the enzymes. Tissue kallikrein also tolerates a P3 proline residue well. In sharp contrast to the behaviour of trypsin is the very strong influence of the P2 residue in tissue-kallikrein-catalyzed reactions. kcat/Km varies 75-fold in the series of the dipeptide esters with nonpolar L-amino acid residues in P2, a P2 glycine residue furnishing the worst and phenylalanine the best substrate, whereas this exchange in the pentapeptides changes kcat/Km as much as 730-fold. This behaviour, together with the high value of kcat/Km for Ac-Phe-Arg-OMe of 3.75 X 10(7) M-1 s-1, suggests rate-limiting binding (k1) in the hydrolysis of the best ester substrates.(ABSTRACT TRUNCATED AT 400 WORDS)

An improved spectrophotometric assay for leucine aminopeptidase

A sensitive assay to determine the activity of leucine aminopeptidase (EC 3.4.11.1), using L-leucine thiobenzyl ester as substrate, was developed. Hydrolysis of the ester by leucine aminopeptidase can be monitored in the presence of 5,5-dithiobis-(2-nitrobenzoic acid) by continuous spectrophotometric measurement at 412 nm. Comparison with some amide substrates showed that the thiol ester provides a much more sensitive assay, its specificity constant (Vmax./Km) being some 3000-fold higher than that of leucine p-nitroanilide.

The action of factor Xa on peptide p-nitroanilide substrates: substrate selectivity and examination of hydrolysis with different reaction conditions

Kinetic parameters for the action of bovine Factor Xa (EC 3.4.21.22) on 25 commercially available peptide p-nitroanilides have been determined. The selectivity constant, kc/Km, ranges from 1.5 X 10(1) to 2 X 10(6) M-1 X s-1 for the poorest and the best substates, respectively. The best substrates for Factor Xa were identified as those with arginine in the P1 position, and glycine in the P2 position. Quantitative distinction between lysine and arginine in the P1 position and other amino acids in the P2-P4 positions of the substrate is reported from the changes in the kinetic parameters for substrates differing in only a single amino acid in these positions. Effect of NaCl and CaCl2 concentrations and temperature on the action of Factor Xa on selected substrates have been assessed. Km values for Factor Xa hydrolysis of most substrates are greater than 100 microM. Solubility of the substrates consequently restricts measurements of reaction velocities to concentrations lower than desirable for optimally determining kc. Comparison of these kinetic parameters for Factor Xa with those of thrombin (Lottenberg, R., Hall, J.A., Blinder, M., Binder, E. and Jackson, C.M. (1983) Biochim. Biophys. Acta 742,539-557) for these same substrates indicates that the greater hydrolytic efficiency of thrombin is due primarily to lower Km values.

Recent evolutionary divergence of plasma prekallikrein and factor XI

The evolution in mammals of the zymogens of the contact activation system of coagulation (factor XII, prekallikrein and factor XI) has been investigated. The NH2-terminal sequences of human plasma prekallikrein and the heavy and light chains of kallikrein have been determined and compared with those of bovine prekallikrein and of human and bovine factors XII and XI. The human and bovine NH2-terminal sequences of the light chains (catalytic polypeptide) show striking similarities both among themselves and with those of the catalytic polypeptide chains of other coagulation and digestive proteases, indicating a common origin. Comparison of the NH2-terminal sequences of human prekallikrein with those of the bovine prekallikrein and human bovine factors XIa and XIIa indicates a common origin of the heavy chain of kallikrein and factor XIa, different from that of either factor XIIa or other known amino acid sequences. Ancestral sequences for human and bovine prekallikrein and factor XI, deduced by genetic analysis of the minimum number of base changes indicate that the NH2-terminus of prekallikrein and factor XI have evolved at about the same rate. The estimated time for the gene duplication was about 124 million years ago, a value consistent with the age of the mammals.

Structure of the product complex of acetyl-Ala-Pro-Ala with porcine pancreatic elastase at 1.65 A resolution

A single crystal of porcine pancreatic elastase was mounted in a thin-walled capillary and allowed to react with acetyl-Ala-Pro-Ala-paranitroanalide. Diffraction data to 1.65 A resolution were measured and the isomorphous structure was solved from the difference Fourier map. The structure contains two surprises. Two molecules of the product: acetyl-Ala-Pro-Ala molecule are bound in the extended binding site. Both molecules are bound backwards with respect to the established mode of peptide binding.

Cotton dust contains proteolytic and elastolytic enzymes not inhibited by alpha-1-proteinase inhibitor

Others have found proteolytic activity in cotton dust and correlated this with the prevalence of acute byssinosis. The present study characterized the proteases in aqueous extracts of cotton dust after controlling for potential artifact from microbial contamination. We tested cotton dust, generated in a model card room operated by the U.S. Department of Agriculture (USDA), for total proteolytic activity (hydrolysis of azocasein) and elastolytic activity (degradation of insoluble 3H-elastin). Both coarse dust and a respirable fraction (aerodynamic diameter less than or equal to 1.7 microgram) yielded proteolytic activity. Proteolysis was inhibited by EDTA (39%), diisopropylfluorophosphate (DFP) (33%) and alpha-1-proteinase inhibitor (alpha 1 PI) (30%), but not by iodoacetic acid or pepstatin. Elastolytic activity was also present, and was inhibited by DFP (80%) and alpha 1 PI (70%), but not by EDTA. We conclude that cotton dust contains preformed metallo- and serine proteases, and serine elastolytic protease(s) which are incompletely inhibited by alpha 1 PI. These findings may be relevant to the development of chronic lung disease in people exposed to cotton dust.

Spectrophotometric assay for vertebrate collagenase

Collagenase from normal human skin fibroblasts was found to catalyze the hydrolysis of esters and thio esters. This observation led to the development of a rapid, sensitive, continuous spectrophotometric assay for vertebrate collagenase using the thio peptolide Ac-ProLeuGly-S-LeuLeuGly-OC2H5 as substrate in the presence of 4,4'-dithiodipyridine or Ellman's Reagent. A Km of 0.004 M and a kcat of 370,000 h-1 were determined for the thio peptolide-enzyme reaction. The method is able to detect collagenase at concentrations as low as 2 ng/ml.

Reaction of serine proteases with substituted isocoumarins: discovery of 3,4-dichloroisocoumarin, a new general mechanism based serine protease inhibitor

The mechanism-based inactivations of a number of serine proteases, including human leukocyte (HL) elastase, cathepsin G, rat mast cell proteases I and II, several human and bovine blood coagulation proteases, and human factor D by substituted isocoumarins and phthalides which contain masked acyl chloride or anhydride moieties, are reported. 3,4-Dichloroisocoumarin, the most potent inhibitor investigated here, inactivated all the serine proteases tested but did not inhibit papain, leucine aminopeptidase, or beta-lactamase. 3,4-Dichloroisocoumarin was fairly selective toward HL elastase (kobsd/[I] = 8920 M-1 s-1); the inhibited enzyme was quite stable to reactivation (kdeacyl = 2 X 10(-5) s-1), while enzymes inhibited by 3-acetoxyisocoumarin and 3,3-dichlorophthalide regained full activity upon standing. The rate of inactivation was decreased dramatically in the presence of reversible inhibitors or substrates, and ultraviolet spectral measurements indicate that the isocoumarin ring structure is lost upon inactivation. Chymotrypsin A gamma is totally inactivated by 1.2 equiv of 3-chloroisocoumarin or 3,4-dichloroisocoumarin, and approximately 1 equiv of protons is released upon inactivation. These results indicate that these compounds react with serine proteases to release a reactive acyl chloride moiety which can acylate another active site residue. These are the first mechanism-based inhibitors reported for many of the enzymes tested, and 3,4-dichloroisocoumarin should find wide applicability as a general serine protease inhibitor.

Kinetics of hydrolysis of peptide thioester derivatives of arginine by human and bovine thrombins

Several peptide thioester substrates have been synthesized and tested with human thrombins (alpha, gamma, and nitrated), bovine thrombin, trypsin, and Factor X alpha beta. The substrates include various thioalkyl esters, thiobenzyl esters with substitution in the 4-position, substrates containing additional residues on the amino-terminal side of the scissile bond (P extended substrates) and one substrate containing additional residues on the carboxyl-terminal side (P' extended substrate). Neither the P nor the P' extensions resulted in significantly increased specificity; however, with one P extended substrate, D-Phe-Pro-Arg-SBzl, the KM with bovine thrombin (0.72 microM) was the second lowest KM yet reported. The results of this study underscore the importance of P vs. P' extension for thrombin substrates. The kinetic constants of the thiobenzyl esters were found to be little affected by the 4-position substitutions. A comparison of gamma-thrombin and nitrothrombin shows them to be quite similar kinetically, while both are significantly less reactive than alpha-thrombin. With these substrates, trypsin, bovine thrombin, and Factor X alpha beta have kcat/KM values in the approximate ratio of 35:10:1, respectively. The results presented here should be of value in the future design of reactive yet specific substrates for thrombin. The comparisons between the various enzymes could be helpful in clarifying the nature of their active sites.

Inhibition of activated porcine factor IX by dansyl-glutamyl-glycyl-arginyl-chloromethylketone

Activated porcine Factor IX is irreversibly inhibited by an active site histidine-directed serine protease inhibitor, dansyl-glutamyl-glycyl-arginyl-chloromethylketone (DEGR-CK). The kinetics of inhibition are second order up to inhibitor concentrations of 10(-5) M. The apparent second-order rate constant (in 0.20 M NaCl, pH 8.0) is 1.7 X 10(4) M-1 min-1, which is considerably lower than values reported for Factor Xa, thrombin, plasmin, and kallikrein. Reaction of increasing concentrations of DEGR-CK with Factor IXa, followed by analysis of residual enzymatic activity, yields 1.2 mol DEGR-CK/mol protein, indicating 1:1 stoichiometry for the DEGR-CK/Factor IXa interaction. DEGR-Factor IXa is a potent anticoagulant in vitro. A concentration of 1 nM causes 50% inhibition of the ability of normal porcine-citrated plasma to correct either Factor VIII- or Factor IX-deficient plasmas (intrinsic pathway factors). In contrast, more than 100 nM DEGR-Factor IXa is required to cause 50% inhibition of Factor VII (extrinsic pathway) or Factor X (common pathway) assays. Activation of porcine Factor VIII:C by thrombin in the presence of DEGR-Factor IXa and phosphatidylcholine-phosphatidylserine vesicles reveals that DEGR-Factor IXa markedly stabilizes the spontaneous loss of Factor VIII:Ca activity as does unmodified Factor IXa [P. Lollar, G.J. Knutson, and D. N. Fass (1984) Blood 63, 1303-1308]. These results suggest that DEGR-Factor IXa incorporates into the intrinsic pathway Factor X-activator enzymatic complex, and also that stabilization of Factor VIII:Ca by this complex is independent of the active site of Factor IXa. Inhibition of Factor IXa by DEGR-CK results in the first reported irreversible active-site-modified derivative of this enzyme. DEGR-CK promises to be a useful reagent in the study of the Factor X activator complex. Conceivably, its specific anticoagulant properties could have future clinical benefit.

Peptide thioesters and 4-nitroanilides as substrates for porcine pancreatic kallikrein

A series of 14 4-nitroanilide substrates and 17 thioester substrates have been used to measure kinetic constants with porcine pancreatic kallikrein. All of the substrates have a P1 arginine residue. The 4-nitroanilide substrates consist of seven P2-glycine and seven P2-phenylalanine tripeptides. As expected from previous results, the phenylalanine series substrates were generally 100-fold 'better' than those in the glycine series. The S3 subsite was found to 'prefer' lysine or phenylalanine, whereas glutamic acid in this position was distinctly unfavourable. The thioester substrates consisted of various thioester derivatives of arginine as well as 12 dipeptides. These substrates exhibited kcat./Km values generally 1000 times higher than the P2-phenylalanine 4-nitroanilides. With the thioesters, a P2 phenylalanine or tryptophan residue yielded the best substrates, but some of the simple derivatives of arginine were nearly as good. A comparison of the kinetic constants of the thioester substrates between the porcine enzyme and human plasma kallikrein provides further evidence that these enzymes have a similar preference for bulky P2 residues, but otherwise are quite different enzymes. The thioester substrates are nearly as reactive as oxygen ester substrates such as acetylphenylalanylarginine methyl ester for the porcine enzyme [Levison & Tomalin (1982) Biochem. J. 203, 299-302; Fiedler (1983) Adv. Exp. Med. Biol. 156A, 263-274], and owing to the greater ease in assaying with the thioesters, they should find use in routine assays for the glandular kallikreins.

Benzyl p-guanidinothiobenzoate hydrochloride, a new active-site titrant for trypsin and trypsin-like enzymes

Benzyl p-guanidinothiobenzoate hydrochloride was synthesized and demonstrated to be useful for active-site titration of bovine trypsin, bovine thrombin, human lung tryptase, bovine activated protein C, human Factor XIIa fragment and bovine Factor Xa beta. The titration is based on rapid formation of a stable acyl-enzyme with a stoichiometric release of benzyl thiol. Thiol production is measured quantitatively by including 4,4'-dithiodipyridine in the reaction mixture and measuring the increase in absorbance at 324 nm. Ellman's reagent has also been successfully employed, allowing measurement at 410 nm. Unlike p-nitrophenyl p'-guanidinobenzoate, the thioester titrant reacts slowly with chymotrypsin A alpha thus eliminating interference by this enzyme in most titrations. Advantages of this reagent as a titrant include: flexibility in detection of the released thiol, selectivity between trypsin and chymotrypsin-like enzymes, minimal pH-dependence of the epsilon of the absorbing species, relative stability of the reagent under titration conditions, and high epsilon at pH 7.2 with either 4,4'-dithiodipyridine or Ellman's reagent. The reagent should prove useful as an alternative to p-nitrophenyl p'-guanidinobenzoate hydrochloride for the determination of active-site concentrations of the enzymes employed, as well as of other related enzymes.

Identification of the molecular defect in factor IX Chapel Hill: substitution of histidine for arginine at position 145

Hemophilia B Chapel Hill is a mild hereditary hemorrhagic disorder in which the factor IX antigen is present in normal amounts but factor IX biological activity is markedly reduced. Previous studies have demonstrated that purified factor IX Chapel Hill has 8% of the activity of normal human factor IX and that the activation of factor IX Chapel Hill is defective in that only one of the two peptide bonds hydrolyzed during activation of normal factor IX is cleaved. The tryptic peptides from normal human factor IX and factor IX Chapel Hill were subjected to analysis by high-performance liquid chromatography. Comparison of the elution profile of the peptides obtained from factor IX Chapel Hill and normal factor IX demonstrated that the tripeptide Leu-Thr-Arg, which is derived from the normal molecule (positions 143-145) immediately amino-terminal from the Arg-Ala peptide bond at 145-146 that is cleaved during the activation of factor IX with factor XIa, was absent in the digest obtained from factor factor IX Chapel Hill. The elongated "activation peptide" from factor factor IX Chapel Hill was obtained by further high-performance liquid chromatographic fractionation and subjected to primary structure analysis. The following sequence, corresponding to positions 143-147, was obtained: Leu-Thr-His-Ala-Glu. Thus, the primary molecular defect in factor factor IX Chapel Hill is the substitution of histidine for arginine at position 145. This substitution precludes cleavage by factor XIa at this peptide bond, and the activation peptide region remains associated with the light chain of factor IXa Chapel Hill.

The action of thrombin on peptide p-nitroanilide substrates. Substrate selectivity and examination of hydrolysis under different reaction conditions

Kinetic parameters for the action of bovine alpha-thrombin on 24 commercially available peptide p-nitroanilides have been determined. The selectivity constant, kcat/Km, ranges from 3.3 X 10(1) to 1.1 X 10(8) M-1 X S-1 for the poorest and the best substrates, respectively. The best substrates for thrombin were identified as those with arginine in the P1 position, proline or a proline homolog in the P2 position, and an apolar amino acid in the P3 position. Quantitative distinction between lysine and arginine in the P1 position and other amino acids in the P2-P4 positions of the substrate is reported from the changes in the kinetic parameters for substrates differing in only a single amino acid in these positions. Effects of NaCl, CaCl2 and poly(ethylene glycol) concentrations, pH and temperature on the action of thrombin on selected substrates have been assessed. A source of large systematic error in thrombin concentration estimates was identified as resulting from adsorption losses. These losses were eliminated by inclusion of poly(ethylene glycol) in dilution and reaction buffers.

Studies on the temperature-dependent autoinhibition of human plasma kallikrein I

At 37 degrees C, human plasma kallikrein I follows Michaelis-Menten behaviour and exhibits a normal linear relationship between the initial velocity of hydrolysis of Ac-Pro-Phe-Arg-OMe,HCl and enzyme concentration in the range 0--150 pM. At temperatures of 30 degrees C and below substantial deviations from linearity are observed over the same enzyme concentration range. The temperature-dependent autoinhibition of kallikrein I activity is reversible and is not due to low-molecular-weight endogenous inhibitors or cofactors. The kinetic effect is apparently due to aggregation and can be abolished by the addition of sodium deoxycholate.