Substrate specificity of the serine proteinase from Bacillus subtilis, strain 72

A comparative study of the hydrolysis of various p-nitroanilide substrates (Z-A2-A1-pNA, Z-A3-A2-A1-pNA, and Z-A4-A3-A2-A1-pNA, where A1-An are various amino acid residues, Z is the benzoyloxycarbonylic group and pNA is the p-nitroanilide group), catalyzed by serine proteinase from Bacillus subtilis strain 72, was carried out. It was found that depending on the substrate structure, the hydrolysis may involve both the peptide-p-nitroaniline and the amino acid-amino acid bonds. A kinetic analysis of substrate hydrolysis occurring simultaneously at these two bonds was carried out. The physico-chemical meaning of the kinetic parameters of the given scheme was determined. The quantitative estimation of the enzyme specificity with respect to both hydrolyzing bonds can be found by using the parameters calculated during the analysis of the kinetic curve of p-nitroaniline production. It was found that according to their specificity the amino acid residues at position A1 can be arranged in the following order: L-Leu greater than P-Phe greater than L-Ile greater than L-Ala. The beta-branched amino acid residues, L-Val and L-Ile, do not bind to subsite S1. If these residues occupy position A1, the substrate splitting occurs exclusively between residues A1 and A2. The tetrapeptide N-protected p-nitroanilide substrates are also hydrolyzed at this bond. Partial hydrolysis of the amino acid-amino acid bond between residues A1 and A2 occurs in two cases: i) when residue A1 is loosely bound to subsite S1 and/or, ii) when residue A2 is firmly bound to subsite S1.     

Peptide synthesis in organic media with the use of subtilisin 72 immobilized on a poly(vinyl alcohol) cryogel

Subtilisin 72 serine protease (EC 3.4.21.14) immobilized on a poly(vinyl alcohol) cryogel was used as a catalyst in the syntheses of N-protected peptide p-nitroanilides of the general formulas Z(or Boc)-Xaa-Phe-pNA (Xaa = Leu or Ala), Z-Ala-Xaa-Yaa-pNA (Xaa = Leu or Ala; Yaa = Leu or Phe), and Z-Ala-Ala-Xaa-Yaa-pNA (Xaa = Leu, Arg, or Gly; Yaa = Phe, Leu, Gly, Asp, or Glu). The syntheses were carried out in DMF-acetonitrile mixtures. A number of protected di-, tri-, and tetrapeptides were prepared in yields up to 99%. The syntheses were found to retain stereoselectivity under the conditions studied. The activation of carboxyl group of the acylating component was shown to have a positive effect upon the coupling rate. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2005, vol. 31, no. 6; see also http://www.maik.ru.     

Residues Leu261, Trp264, and Phe265 account for apolipoprotein E-induced dyslipidemia and affect the formation of apolipoprotein E-containing high-density lipoprotein

Overexpression of apolipoprotein E (apoE) induces hypertriglyceridemia in apoE-deficient mice, which is abrogated by deletion of the carboxy-terminal segment of residues 260-299. We have used adenovirus-mediated gene transfer in apoE-/- and apoA-I-/- mice to test the effect of three sets of apoE mutations within the region of residues 261-265 on the induction of hypertriglyceridemia, the esterification of cholesterol of very low-density lipoprotein (VLDL) and high-density lipoprotein (HDL), and the formation of spherical or discoidal apoE-containing HDL. A single-amino acid substitution (apoE4[Phe265Ala]) induced hypertriglyceridemia in apoE-/- or apoA-I-/- mice, promoted the accumulation of free cholesterol in the very low-density lipoprotein (VLDL) and HDL region, and decreased HDL cholesterol levels. A double substitution (apoE4[Leu261Ala/Trp264Ala]) induced milder hypertriglyceridemia and increased HDL cholesterol levels. A triple substitution (apoE4[Leu261Ala/Trp264Ala/Phe265Ala] or apoE2[Leu261Ala/Trp264Ala/Phe265Ala]) did not induce hypertriglyceridemia and increased greatly the HDL cholesterol levels. Electron microscopy (EM) analysis of the HDL fractions showed that apoE4[Leu261Ala/Trp264Ala/Phe265Ala] and apoE2[Leu261Ala/Trp264Ala/Phe265Ala] contained spherical HDL, apoE4[Leu261Ala/Trp264Ala] contained mostly spherical and few discoidal HDL particles, and apoE4[Phe265Ala] contained discoidal HDL. We conclude that residues Leu261, Trp264, and Phe265 play an important role in apoE-induced hypertriglyceridemia, the accumulation of free cholesterol in VLDL and HDL, and the formation of discoidal HDL. Substitution of these residues with Ala improves the apoE functions by preventing hypertriglyceridemia and promoting formation of spherical apoE-containing HDL.     

Proline-containing β-turns in peptides and proteins. II. Physicochemical studies on tripeptides with the Pro-Gly sequence

Amino acids are known to differ in their individual preferences for each of the four positions of the β-turn conformation formed by tetrapeptide segments. Proline and glycine show relatively high preferences for positions 2 and 3, respectively, of the β-turn. Using tripeptides of the type N-acetyl-Pro-Gly-X-OH, where X = Gly, Ala, Leu, Ile, and Phe, we have sought to study the influence of the 4th residue X on the stability of the β-turn conformation in these tripeptides. Our nmr and CD results show that the β-turn stability is quite significantly governed by the nature of the amino acid residue at this position in the following order: Leu > Ala > Ile, Gly > Phe.     

Alkaline serine proteinases D and E of Streptomyces griseus K-1.

Two DFP-sensitive alkaline proteinases with strong esterase activity toward Ac-(Ala)3-OMe, designated as alkaline serine proteinases D and E, were purified pronase, a protease mixture from St. griseus K-1. Each was shown to be homogeneous by acrylamide disc gel electrophoresis. The molecular weights of these enzymes were estimated to be about 27,000 be gel filtration. Studies on their actions on acyl-tl-amino acid methyl or ethyl esters indicated that proteinases D and E both exhibited a broad substrate specificity and hydrolyzed the ester bonds of esters containing Trp, Tyr, Phe, Leu, and Ala. The esterase activities of both enzymes toward Ac-(Ala)3-OMe were the highest among proteinases so far isolated from various sources. Proteinases D and E also lacked cystine residues in their molecules, being entirely different from alkaline serine proteinases A, B, and C in pronase. Some differences were , however, observed between them as regards pH stability, behavior on CM-cellulose, mobility on polyacrylamide electrophoresis, and amidase activity toward Suc-(Ala)3-pNA.     

Postprandial body protein synthesis and amino acid catabolism measured with leucine and phenylalanine-tyrosine tracers

Whether phenylalanine-tyrosine (Phe-Tyr) tracers yield estimates of postprandial protein synthesis comparable to those of the widely used leucine (Leu) tracer is unclear. We measured Leu oxidation (Ox), Phe hydroxylation (Hy), and their disposal into whole body protein synthesis before and after the administration of a mixed meal (62 kJ/kg body wt, 22% of energy as protein), over 4 h in healthy subjects. Both plasma and intracellular precursor pools were used. The amino acid data were extrapolated to body protein by assuming a fixed ratio of Leu to Phe in the proteins. In the postabsorptive state, whole body protein synthesis (expressed as mg. kg(-1). min(-1)) was similar between Leu and Phe-Tyr tracers irrespective of the precursor pool used. After the meal, Leu Ox, Phe Hy, and body protein synthesis increased (P < or = 0.01 vs. basal). With the use of intracellular precursor pools, the increase of protein synthesis with Phe-Tyr (+0.51 +/-0.21 mg. kg(-1). min(-1)) and Leu tracers (+0.57 +/- 0.14) were similar (P = not significant). In contrast, with plasma pools the increase of protein synthesis was more than twofold greater with Phe-Tyr (+1.17 +/- 0.19 mg. kg(-1). min(-1)) than that with Leu (0.50 +/- 0.13 mg. kg(-1). min(-1), P < 0.01). Direct correlations were found between Leu and Ox [using both plasma and intracellular pools (r < or = 0.65, P < or = 0.01)] but not between Phe and either plasma or intracellular Hy. In conclusion, 1) Phe-Tyr and Leu tracers yield comparable estimates of body protein synthesis postprandially, provided that intracellular precursor pools are used; 2) both Leu Ox and Phe Hy are stimulated by a mixed meal; 3) Phe does not correlate with Hy, which might be better related to the (unknown) portal Phe.     

Purification and characterization of the neutral endopeptidase from human kidney

The presence of an endopeptidase hydrolyzing succinyl trialanine-p-nitroanilide [Suc(Ala)3-pNA] to Suc(Ala)2 and Ala-pNA in human kidney and its partial characterization have been reported (Ishida et al. (1981) Biochem. Int. 3, 239-246). This neutral metallo-endopeptidase was separated into two fractions (A and B) on Sephacryl S-300 and fraction B was further purified to an electrophoretically pure state. The fraction B enzyme had a molecular weight of 100,000 and was inhibited by metal chelators such as EDTA, o-phenanthroline and phosphoramidon, but not by serine protease inhibitors. The enzyme was found to hydrolyze peptide bonds preferentially at the amino sides of hydrophobic amino acids such as Leu and Phe, when its specificity was studied using insulin B chain and angiotensin I. Fraction A seems to be a tetramer of fraction B, judging from its molecular weight, pI, substrate specificity and immunological properties.     

Identification of coding polymorphisms in human circadian rhythm genes PER1, PER2, PER3, CLOCK, ARNTL, CRY1, CRY2 and TIMELESS in a multi-ethnic screening panel.

STUDY OBJECTIVE: In this study, the exonic regions of the circadian rhythm genes PER1, PER2, PER3, CLOCK, ARNTL, CRY1, CRY2 and TIMELESS were re-sequenced and coding changes identified in a panel of 95 individuals varying in ethnicity. STUDY PARTICIPANTS: DNA screening panel consisting of 95 DNA samples (17 American Caucasians, 17 African Americans, 8 Ashkenazi Jews, 8 Chinese, 8 Japanese, 5 Mexican Indians, 8 Mexicans, 8 Northern Europeans, 8 Puerto Ricans, and 8 South Americans) selected from the Coriell Institute Human Variation Panel. RESULTS: In addition to coding changes already identified in the database dbSNP, novel coding changes were identified, including PER1: Pro37Ser, Pro351Ser, Gln988Pro, Ala998Thr; PER2: Leu83Arg, Leu157Leu, Thre174Ile, Phe400Phe, Pro822Pro, Ala828Thr, Ala861Val, Phe876Leu, Val883Met, Val903Ile, Ala923Pro; PER3: Pro67Pro, Val90Ile, His638His, Ala820Ala, Leu929Leu; ARNTL: Arg166Gln, Ser459Phe; CLOCK: Ala34Ala, Ser208Cys, Phe233Phe, Ser632Thr, Ser816Ser; TIMELESS: Met870Val and CRY2: His35His. No coding polymorphisms were identified in CRY1. CONCLUSIONS: Considerable genetic variation occurs within the coding region of the genes regulating circadian rhythm. Many of the non-synonymous coding polymorphisms could affect protein structure/function with the potential to affect molecular regulation of the sleep/wake cycle. Many of the potential functional effects could be ethnic group specific.     

Chemical replacement of P1' arginine residue at the first reactive site of peanut protease inhibitor B-III

The contribution of the P1' residue at the first reactive site of peanut protease inhibitor B-III to the inhibition was analyzed by replacement of the P1' Arg(11) with other amino acids (Arg, Ser, Ala, Leu, Phe, Asp) after selective modification of the second reactive site. The Arg derivative had the same trypsin inhibitory activity as the native inhibitor (Ki = 2 X 10(-9) M). The Ser derivative inhibited more weakly (Ki = 2 X 10(-8) M). The Ala and Leu derivatives inhibited trypsin very weakly (Ki = 2 X 10(-7) M and 4 X 10(-7) M, respectively), and the Phe and Asp derivatives not at all. These results suggest that the P1' arginine residue is best for inhibitory activity at the first reactive site of B-III, although it has been suggested that a P1' serine residue at the reactive site is best for inhibitory activity of Bowman-Birk type inhibitors.     

Isolation and properties of serine proteinase from Aspergillus oryzae

A serine proteinase having an activity optimum at pH 6.7-8.2 has been isolated from amylorisine P-10x (a mixture of Aspergillus oryzae enzymes) by chromatography on DEAE-Sephadex A-50 and bacitracin Sepharose 4B. The proteinase is fully inactivated by phenylmethylsulfonylfluoride and diisopropylfluorophosphonate, the specific inhibitors of the enzyme, and has a pI at pH 7.5. The molecular mass of serine proteinase is 30000 Da; its amino acid composition appears as: Met2, Asp33, Thr18, Ser29, Glu21, Pro9, Glu32, Ala38, Val24, Ile16, Leu15, Tyr8, Phe8, His8, Lys18, Arg4, Trp6. The N-terminal sequence of the serine proteinase: Gly-Leu-Thr-Thr-Gln-Lys-Ser-Ala-Pro-Trp-Gly-Leu-Gly-Ser-Ile-Ser-Xaa-Lys- Gly-Gln-Gln-Ser-Thr-Asp-Tyr-Ile-Tyr, which coincides practically completely with the corresponding sequence of alkaline proteinase of A. oryzae, ATCC20386, has been determined. Similar to subtilisin, the enzyme catalyzes the condensation of leucine and alanine p-nitroanilides with N-benzyloxycarbonyl-alanyl-alanine and glycyl-alanine methyl esters.     

A novel site-directed mutant of myoglobin with an unusually high O2 affinity and low autooxidation rate.

Mutants of sperm whale myoglobin were constructed at position 29 (B10 in helix notation) to examine the effects of distal pocket size on the rates of ligand binding and autooxidation. Leu29 was replaced with Ala, Val, and Phe using the synthetic gene and Escherichia coli expression system of Springer and Sligar (Springer, B. A., and Sligar, S. G. (1987) Proc. Natl. Acad. Sci. U. S. A. 84, 8961-8965). Structures of the ferric forms of Val29 and Phe29, and the oxy form of Phe29 myoglobin were determined to 1.7 A by x-ray crystallography. The ferric mutant proteins are remarkably isomorphous with the wild type protein except in the immediate vicinity of residue 29. Thus, the protein structure in the distal pocket of myoglobin can accommodate either a large "hole" (i.e. Ala or Val) or a large side chain (i.e. Phe) at position 29 without perturbation of tertiary structure. Phe29 oxymyoglobin is also identical to the native oxy protein in terms of overall structure and interactions between the bound O2 and His64, Val68, Phe43, and Ile107. The distance between the nearest side chain atom of residue 29 and the second atom of the bound oxygen molecule is 3.2 A in the Phe29 protein and 4.9 A in native myoglobin. The equilibrium constants for O2 binding to Ala29, Val29, and Leu29 (native) myoglobin are the same, approximately 1.0 x 10(6) M-1 at 20 degrees C, whereas that for the Phe29 protein is markedly greater, 15 x 10(6) M-1. This increase in affinity is due primarily to a 10-fold decrease in the O2 dissociation rate constant for the Phe29 mutant and appears to be the result of stabilizing interactions between the negative portion of the bound O2 dipole and the partially positive edge of the phenyl ring. Increasing the size of residue 29 causes large decreases in the rate of autooxidation of myoglobin: k(ox) = 0.24, 0.23, 0.055, and 0.005 h-1 for Ala29, Val29, Leu29 (native), and Phe29 myoglobin, respectively, in air at 37 degrees C. Thus, the Leu29----Phe mutation produces a reduced protein that is remarkably stable and is expressed in E. coli as 100% MbO2. The selective pressure to conserve Leu29 at the B10 position probably represents a compromise between reducing the rate of autooxidation and maintaining a large enough O2 dissociation rate constant to allow rapid oxygen release during respiration.     

Structure-activity relationship of endothelin: importance of charged groups

Endothelin (ET)-related peptides including ET-1 (1-39) were synthesized, and their constricting activity in rat pulmonary artery rings and pressor activity in unanesthetized rat were measured to elucidate their structure-activity relationship. The vasoconstrictor activities of ET-2, ET-3 and sarafotoxin S6b were one-half, one-60th and one-third that of ET-1, respectively. Such differences in biological activities should mainly arise from sequence heterogeneity at the N-terminal portion, especially at positions 4 to 7. All of the blocked ETs at the amino or carboxyl termini showed greatly decreased activities. A monocyclic analog, in which Cys3 and Cys11 were replaced by Ala, showed one-third the activity of ET-1; however, its deamino dicarba analog was almost completely inactive. Significant activities were retained even with replacement of amino acids at positions Ser4, Ser5, Leu6, Met7, Lys9, Tyr13, and Trp21 by Ala, Ala, Gly, Met(0), Leu, Phe, and Tyr or Phe, respectively. On the other hand, replacement of Asp8, Glu10 and Phe14 by Asn, Gln and Ala, respectively, resulted in complete loss of the biological activity. These results indicated that two disulfide bonds in ET molecule were not essential for the expression of vasoconstricting activity. Both terminal amino and carboxyl groups, carboxyl groups of Asp8 and Glu10, and the aromatic group of Phe14 seemed to be contributing, more or less, to the expression of the biological activities.     

Kinetics of dipeptidyl peptidase IV proteolysis of growth hormone-releasing factor and analogs.

The kinetics and selectivity of proteolysis of synthetic human growth hormone-releasing factor and analogs by purified human placental dipeptidyl peptidase IV (DPP IV) were studied by HPLC. The initial rates of Ala2-Asp3 cleavage (pH 7.8, 37 degrees C, So = 0.15 mM) were all approx. 5 mumol min-1 mg-1 for the parent hormone, GRF(1-44)-NH2, and the fragments, GRF(1-29)-NH2 and GRF(1-20)-NH2. Lower activities observed for GRF(1-11)-OH, GRF(1-3)-OH, and cyclic lactam analogs indicate S1'-Sn' binding. Assays of [Trp6]-GRF(1-29)-NH2 versus [D-Trp6]-GFR(1-29)-NH2 indicate an S4' binding cavity. Peptides with D-configuration at P2, P1 or P1' and desNH2Tyr1 and N-MeTyr1 analogs of GRF were not cleaved. Catalytic parameters for the P1-substituted analogs [X2,Ala15]-GRF(1-29)-NH2 were found to vary with X as follows, Km: Abu less than Ala less than Pro less than Val less than Ser less than Gly much less than Leu; kcat: Pro greater than Ala greater than Abu greater than Ser greater than Gly much greater than Leu greater than Val; kcat/Km: Abu greater than Pro greater than Ala much greater than Ser greater than Gly = Val much greater than Leu. Km is at a minimum and kcat/Km at a maximum, for a hydrophobic P1 side-chain of about 0.25 nm in length, i.e., the ethyl side-chain of alpha-aminobutyric acid (Abu) is very close to optimal. These results further define the S1 selectivity of DPP IV and may be useful in the design of DPP IV resistant GRF analogs that can be produced by recombinant DNA methods and the design of DPP IV inhibitors.     

Effect of terminal achiral and chiral residues on the conformational behaviour of poly Δ(z)Phe and analysis of various interactions

Conformational properties of the peptides containing (Δ(Z)Phe)6 with achiral (ΔAla, Gly) and chiral (Ala, Leu) residues at both the N- and C-terminal positions have been studied with a view to design a peptide with desired helical screw sense. In all the peptides, the lowest energy conformational state corresponds to Φ = 0° and Ψ = + 90° or - 90° or both +/- 90°. These structures are characterized by rise per residue of 1.94 ?; rotation per residue of 114° and 3.12 residues per turn and are stabilized by: (i) carbonyl-carbonyl interactions with the carbonyl oxygen of ith residue and carbonyl carbon atom of the carbonyl group of ith+1 residue; and (ii) N-H....π interactions between the amino group of Δ(Z)Phe and its own aromatic moiety. The Ala/Leu residues at the N-terminus further stabilized the structure, through C-H....π interactions with the farthest edge of the aromatic ring of ith+3 Δ(Z)Phe residue. For peptides Ac-L-Ala/L-Leu-(Δ(Z)Phe)6-NHMe, the low energy left handed helical structure (approximately 2.5 Kcalmol?1 higher in energy) state corresponds to Φ = -30°, Ψ = 120° for L-residue and Φ = Ψ = 30° for Δ(Z)Phe residues and is in good agreement with the X-ray crystallography results for the peptide Boc-L-Ala-(Δ(Z)Phe)4-NHMe crystals grown from acetonitrile/ethanol mixture. Computational results suggest that the peptides Ac-DAla/D-Leu-(Δ(Z)Phe)6-NHMe adopt a right handed helical structure in polar solvents with Φ = 30°, Ψ = -120° for D-residues and Φ = Ψ = -30° for Δ(Z)Phe residues. Both in the left handed and right handed structures, the carbonyl oxygen of acetyl group is involved in 10-membered hydrogen bonded ring formation with NH of 3rd Δ(z)Phe residue whereas Δ(Z)Phe residues backbone adopts a 3?? helix structure. Computational results also suggest that the conformational state with Φ = 0° and Ψ = 90° can be realized by keeping D-Ala or D-Leu at the C-terminal. There is hardly any effect of achiral residues Gly/ΔAla on the conformational behaviour of poly-Δ(Z)Phe.     

Factor VIII light chain contains a binding site for factor X that contributes to the catalytic efficiency of factor Xase

Factor (F) VIII functions as a cofactor in FXase, markedly accelerating the rate of FIXa-catalyzed activation of FX. Earlier work identified a FX-binding site having μM affinity within the COOH-terminal region of the FVIIIa A1 subunit. In the present study, surface plasmon resonance (SPR), ELISA-based binding assays, and chemical cross-linking were employed to assess an interaction between FX and the FVIII light chain (A3C1C2 domains). SPR and ELISA-based assays showed that FVIII LC bound to immobilized FX (K(d) = 165 and 370 nM, respectively). Furthermore, active site-modified activated protein C (DEGR-APC) effectively competed with FX in binding FVIII LC (apparent K(i) = 82.7 nM). Western blotting revealed that the APC-catalyzed cleavage rate at Arg(336) was inhibited by FX in a concentration-dependent manner. A synthetic peptide comprising FVIII residues 2007-2016 representing a portion of an APC-binding site blocked the interaction of FX and FVIII LC (apparent K(i) = 152 μM) and directly bound to FX (K(d) = 7.7 μM) as judged by SPR and chemical cross-linking. Ala-scanning mutagenesis of this sequence revealed that the A3C1C2 subunit derived from FVIII variants Thr2012Ala and Phe2014Ala showed 1.5- and 1.8-fold increases in K(d) for FX, whereas this value using the A3C1C2 subunit from a Thr2012Ala/Leu2013Ala/Phe2014Ala triple mutant was increased >4-fold. FXase formed using this LC triple mutant demonstrated an ~4-fold increase in the K(m) for FX. These results identify a relatively high affinity and functional FX site within the FVIIIa A3C1C2 subunit and show a contribution of residues Thr2012 and Phe2014 to this interaction.     

Anionic inhibitors of pancreatic and leukocyte elastase. Alkylamides of 3-carboxypropionyl- and 4-carboxybutyrylalanine peptides

Low-molecular inhibitors of pancreatic and leukocyte elastase were synthesized of the general formula X-[Ala]n-A [X = Suc and Glt, A = ethylamide, n = 1, 2, 3 and 4; for n = 2 X = H and A = (2-phenylethyl)amide] and of the formula X-[Ala]3-A (X = H, Suc and Glt, A = methyl-, ethyl-, propyl-, isopropyl-, butyl-, isobutyl-, (2-phenylethyl)- and diethylamide; for A = ethylamide, X = maleyl or acetyl). Inhibition constants Ki of these pancreatic and leukocyte elastase inhibitors were determined using the chromogenic substrates Suc-[Ala]4-Nan or Glt-[Ala]4-Nan and Glt-[Ala]3-Val-Nan, respectively. The series of anionic inhibitors containing three alanine residues has the best inhibitory properties. Of the acyl groups, 4-carboxybutyryl appears most advantageous, propylamide is the most suitable of alkylamides for pancreatic elastase, and isobutylamide for leukocyte elastase. Peptides containing a free amino group show an inhibition for pancreatic elastase lower by one order than that of the corresponding acylated derivatives. Glt-[Ala]3-NH-Pr is the best inhibitor of pancreatic elastase with Ki = 0.003mM and Suc-[Ala]3-NH-iBu is the best inhibitor of leukocyte elastase with Ki = 0.7mM.     

Substrate specificity of cucumisin on synthetic peptides

The substrate specificity of cucumisin [EC 3.4.21.25] was identified by the use of the synthetic peptide substrates Leu(m)-Pro-Glu-Ala-Leu(n) (m = 0-4, n = 0-3). Neither Pro-Glu-Ala-Leu (m = 0) nor Leu-Pro-Glu-Ala (n = 0) was cleaved by cucumisin, however other analogus peptides were cleaved between Glu-Ala. The hydrolysis rates of Leu(m)-Pro-Glu-Ala-Leu increased with the increase of m = 1 to 2 and 3, but was however, essentially same with the increase of m = 3 to 4. Similarly, the hydrolysis rates of Leu-Leu-Pro-Glu-Ala-Leu(n) increased with the increase of n = 0 to 1 and 2, but was essentially same with the increase of n = 2 to 3. Then, it was concluded that cucumisin has a S5-S3' subsite length. In order to identify the substrate specificity at P1 position, Leu-Leu-Pro-X-Ala-Leu (X; Gly, Ala, Val, Leu, Ile, Pro, Asp, Glu, Lys, Arg, Asn, Gln, Phe, Tyr, Ser, Thr, Met, Trp, His) were synthesized and digested by cucumisin. Cucumisin showed broad specificity at the P1 position. However, cucumisin did not cleave the C-terminal side of Gly, Ile, Pro, and preferred Leu, Asn, Gln, Thr, and Met, especially Met. Moreover, the substrates, Leu-Leu-Pro-Glu-Y-Leu (Y; Gly, Ala, Ser, Leu, Val, Glu, Lys, Phe) were synthesized and digested by cucumisin. Cucumisin did not cleave the N-terminal side of Val but preferred Gly, Ser, Ala, and Lys especially Ser. The specificity of cucumisin for naturally occurring peptides does not agree strictly with the specificity obtained by synthetic peptides at the P1 or P1' position alone, but it becomes clear that the most of the cleavage sites on naturally occurring peptides by cucumisin contain suitable amino acid residues at P1 and (or) P1' positions. Moreover, cucumisin prefers Pro than Leu at P2 position, indicating that the specificity at P2 position differs from that of papain.     

Peptide synthesis catalyzed by subtilisin-72 in organic solvents

The solubility, stability, and activity of native subtilisin 72 and of its complex with SDS were comparatively studied in a number of polar organic solvents. Subtilisin was found to catalyze peptide bond formation when suspended in acetonitrile or solubilized as a complex with SDS in ethanol and isopropanol. Tripeptide Z-Ala-Ala-Leu-pNA, tetrapeptides A-Ala-Ala-P1-P1'-B, where A = Z or Abz; P1 = Leu, Phe, Met, Trp, Ile, Tyr, Phe(NO2), or Glu(OMe), P1' = Leu, Phe, Glu, Ala, Ile, Val, or Arg; B = NH2, pNA, or 2-(2,4-dinitrophenyl)aminoethylamine residue (Ded); pentapeptides Z-Ala-Ala-Leu-Ala-Ala-pNA and Z-Ala-Ala-Leu-Ala-Phe-pNA; and hexapeptide Abz-Val-Ala-Phe-Phe-Ala-Ala-Ded were synthesized using the SDS-subtilisin complex. The complex also efficiently catalyzed the oligomerization of tripeptide H-Phe-Ala-Leu-OCH3 in ethanol, which resulted in a 63:37 mixture of trioligomer and tetraoligomer. It was demonstrated that SDS-subtilisin is a much more efficient catalyst than the suspension of native enzyme.     

Sequences of tryptic peptides containing the five cysteinyl residues of ribulosebisphosphate carboxylase/oxygenase from Rhodospirillum rubrum

Tryptic peptides which account for all five cysteinyl residues in ribulosebisphosphate carboxylase/oxygenase from Rhodospirillum rubrum have been purified and sequenced. Collectively, these peptides contain 94 of the approximately 500 amino acid residues per molecule of subunit. Due to one incomplete cleavage at a site for trypsin and two incomplete chymotryptic-like cleavages, eight major radioactive peptides (rather than five as predicted) were recovered from tryptic digests of the enzyme that had been carboxymethylated with [³H]iodoacetate. The established sequences are: GlyTyrThrAlaPheValHisCys¹Lys TyrValAspLeuAlaLeuLysGluGluAspLeuIleAla GlyGlyGluHisValLeuCys¹AlaTyr AlaGlyTyrGlyTyrValAlaThrAlaAlaHisPheAla AlaGluSerSerThrGlyThrAspValGluValCys¹ ThrThrAsxAsxPheThrArg AlaCys¹ThrProIleIleSerGlyGlyMetAsnAla LeuArg ProPheAlaGluAlaCys¹HisAlaPheTrpLeuGly GlyAsnPheIleLys In these peptides, radioactive carboxymethylcysteinyl residues are denoted with asterisks and the sites of incomplete cleavage with vertical wavy lines. None of the peptides appear homologous with either of two cysteinyl-containing, active-site peptides previously isolated from spinach ribulosebisphosphate carboxylase/oxygenase.     

New fluorescent substrates for metalloendopeptidases with internal quenching of fluorescence

p-Nitroanilides of antranyloyltripeptides of the general structure Abz-Ala-Ala-P'1-pNA (P'1 = Phe, Leu, Ile, Val) containing intramolecularly quenched fluorescent groups (Abz is a fluorogenic group and pNA is a quencher of fluorescence) were prepared by combination of chemical and enzymatic methods. Thermolysin and metalloproteinases from Legionella pneumophila and Thermoactinomyces species were shown to hydrolyse Ala-P'1 bond of the peptides with simultaneous 4-7 fold increase in fluorescence. Kinetic parameters for enzymatic hydrolysis of the substrates were determined. Metalloendopeptidases can be assayed in the presence of serine proteinases (of the subtilisin type) using Abz-Ala-Ala-Ile-pNA or Abz-Ala-Ala-Val-pNA.