Trennung und Reinigung von Pankreaskallikreinen

Design of novel affinity adsorbents for the purification of trypsin-like proteases

A number of ligands for the selective purification by affinity chromatography of the trypsin-like protease, porcine pancreatic kallikrein, were designed de novo by computer-aided molecular design. The ligands were designed to mimic the side-chains of a number of arginyl dipeptides and included a benzamidine moiety substituted on a triazine ring. The ligands displayed inhibitory activities against pancreatic kallikrein which mirrored the specificity constants of the dipeptides they were designed to mimic. The ligand with the highest affinity for the enzyme, an analogue of a Phe-Arg dipeptide, when immobilized to Sepharose CL-4B via a hexamethylene spacer arm, purified pancreatic kallikrein 110-fold in one step from a crude pancreatic acetone extract.

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)

The pH dependence of pre-steady-state and steady-state kinetics for the porcine pancreatic β-kallikrein-B-catalyzed hydrolysis of p-nitrophenyl ester

Pre-steady-state and steady-state kinetics of the porcine pancreatic beta-kallikrein-B (EC 3.4.21.35) catalyzed hydrolysis of ZArgONp have been determined between pH 2.4 and 8. The results are consistent with a minimum three-step mechanism involving an acyl-enzyme intermediate: (see formula). The formation of the E X S complex may be regarded as a pseudoequilibrium process; the minimum values for k+1 are 5.9 X 10(6) M-1 X s-1 (pH 5.5) and 9.4 X 10(5) M-1 X s-1 (pH 2.4) and that for k-1 is 600 s-1. The value of k-1/k+1 (= Ks) changes from 102 microM at pH greater than or equal to 5.5 to 638 microM at pH less than 2.4. The pH dependence of k+2 conforms to two ionizing groups, in the E X S complex, with pKa values of 3.4 +/- 0.1 and 7.05 +/- 0.10. The pH profile of k+2/Ks (= kcat/Km) reflects the ionization of two groups, in the free enzyme, with pKa values of 4.2 +/- 0.1 and 7.05 +/- 0.10. The pH dependence of k+3 implicates two ionizing groups in the deacylation step with pKa values of 4.6 +/- 0.1 and 7.0 +/- 0.1. At acid pH values (pH 2.4-4.4), k+3 is rate-limiting in catalysis, whereas for pH values higher than 4.4, k+2 becomes rate-limiting. The observed neutral and acid ionizations probably reflect the acid-base equilibrium of His-57 and Asp-189 involved in the central site of beta-kallikrein-B. The structural basis for the specificity and catalytic behaviour of this proteinase are discussed and a role for Ser-226 is pinpointed.

On the various forms of the glandular kallikrein from autolyzed porcine pancreas

Kallikrein C, a minor form of the glandular kallikrein isolated form autolyzed porcine pancreas, has the same amino acid composition a porcine pancreatic beta-kallikreins A and B and comparable specific activity, but a much lower carbohydrate content. Dodecyl sulfate electrophoresis of the reduced enzyme indicated that it is composed of the same two polypeptide chains as the other pancreatic beta-kallikreins of the pig. The carbohydrate content of the two chains of beta-kallikrein B has been determined. Both the A and the B chain of beta-kallikreins from autolyzed porcine pancreas exist in a high-molecular (h) and a low-molecular (1) form which evidently differ only in their carbohydrate content. beta-Kallikrein B has the composition AhBh, beta-kallikrein A, AhB1, and beta-kallikrein C, A1B1. The properties of kallikrein III from porcine pancreas, recently described by Kira et al. (Adv. Exp. Med. Biol. 120A (1979) 273--290), indicate that is is the fourth conceivable form, A1Bh. A preparation of porcine pancreatic kallikrein d2 was found to have a specific activity comparable to that of other kallikrein preparations. Besides a main component migrating like pancreatic beta-kallikrein A, it also contained beta-kallikreins B and C. All four species of chains were observed to occur in this batch of the enzyme. Zuber and Sache (Biochemistry 13 (1974) 3098--3110) reported the resolution of porcine pancreatic kallikreins d1 and d2 into three electrophoretic components each after reduction. Evidently, all these preparations consist of a mixture of several forms of two-chain pancreatic beta-kallikrein.

The primary structure of porcine glandular kallikreins

The amino acid sequence of the A- and B-chains of porcine pancreatic kallikrein B is presented and compared to that of porcine trypsin. The overall homology between both enzymes is 37% identical residues in corresponding position and 51% chemically similar resideus. Comparison of the sequences with the crystal structure of bovine trypsin reveals that the trypsin "autolysis loop" is enlarged in kallikrein by two residues but lacks the basic residue at the cleavage site. Substitutions at the calcium-binding site of trypsin which include Arg 70 for Glu 70 possibly interfere with ion binding. Insertions between trypsin residues 95 and 96 obviously form a new kallikrein "autolysis loop" containing the site of cleavage between the A- and B-chains. One carbohydrate moiety is attached to this surface loop at Asn 95, the second to Asn 239 at the same edge of the globular molecule. The residues at the surface of the substrate binding site are substituted to an extent of 85% while the residues forming contacts to the trypsin inhibitor (Kunitz) are highly preserved. Immunodiffusion studies as well as identity of the N-terminal sequences of pancreatic, submandibular and urinary kallikrein reveal the same genetic origin of the three glandular kallikreins.

Substrate specificity of porcine pancreatic kallikrein

The primary specificity of porcine pancreatic kallikrein is directed predominantly against arginyl and much less so against lysyl bonds. In addition, the enzyme exhibits pronounced secondary specificity for a bulky residue, preferentially phenylalanine, in position P2 of substrates. This feature is found also in porcine submandibular and urinary and in human urinary kallikrein, but not in bovine trypsin. Residues in P3 and P1' and P1' to P3' also affect hydrolysis by pancreatic kallikrein distinctly more than tryptic hydrolysis. The hexapeptide Pro-Phe-Arg-Ser-Val-Gln with the sequence of bovine kininogen around the C-terminus of kinin contains all the structural elements essential for the interaction with kallikrein, and even glutamine appears dispensable. In contrast to ester models for this site, peptidyl methionine esters with the structure of kininogen towards the N-terminus of kinin, notably bulky leucine in P2, are very poor kallikrein substrates, and appear to be of no value as models for the cleavage of kininogen under formation of kallidin.