Novel chromophore substrates of aspartyl proteinases

Chromophore substrates Dnp-Ala-Glu-Phe-Ala-Arg-NH2 and Dnp-Ala-Ala-Phe-Nle-Ala-Arg-NH2 of aspartic proteases were synthesized by a combination of chemical and enzymic methods. The kinetic parameters of their hydrolysis with pepsin, aspergyllopepsin, and chymosin were determined. The introduction of Nle in the P1' position gives stable enzyme-substrate complexes with pepsin and chymosin. A Glu residue at the P2 position contributes significantly to an increase in kcat for the chymosin hydrolysis.     

Direct modifications of the cyclic peptide Polymyxin B leading to analogues with enhanced in vitro antibacterial activity

Synthetic modifications have been made directly to the cyclic peptide core of polymyxin B, enabling the further understanding of structure activity relationships of this antimicrobial peptide. Such modified polymyxins are also substrates for enzymic hydrolysis, enabling the synthesis of a variety of semi-synthetic analogues, resulting in compounds with increased in vitro antibacterial activity.     

Synthesis of choline and ethanolamine phospholipids with thiophosphoester bonds as substrates for phospholipase C.

Spectrophotometric assays of esterases are sensitive, rapid, and quite specific when thioester substrates are used. Glycerophospholipids with thiophosphoester bonds may be useful as substrates for phospholipase C (EC 3.1.4.3). These have been made from mercaptoglycerol and mercaptoethanol. The thiols were oxidized to disulfides, acylated, and reduced with dithiothreitol. Phosphocholine derivatives were made by the classical methods for oxyphosphoesters. The phosphatidyl choline analogue was converted to the phosphatidyl ethanolamine analogue by transphosphatidylation with cabbage phospholipase D and ethanolamine. Structures were proved with enzymic hydrolysis, infrared spectra, TLC behavior, and elemental analyses. The synthesized compounds were rac-1-S-phosphocholine-2,3-O-didecanoyl-1-mercapto-2,3-propanediol, 1-S-phosphoethanolamine-2,3-O-didecanoyl-1-mercapto-2,3-propanediol, and 1-S-phosphocholine-2-O-hexadecanoyl-1-mercapto-2-ethanol.     

The study of hydrolysis of new lipid-like substrates and trilaurin in monolayers catalyzed with the lipase from Pseudomonas fluorescens

A simple method for determining the enzymic hydrolysis parameters of lipid-like substrates and trilaurin assembled in monolayers at the water-air interface was suggested. At a surface pressure of 10 mN/m, the initial rates of lipolysis were found to be proportional to the decrease in area of the substrate monolayer caused by the enzymic hydrolysis in a single-compartment Langmuir balance. The kinetic parameters for the hydrolysis of trilaurin and three 1,3-dilaurylpseudoglycerides acetylated in position 2 with an amino acid (phenylalanine, leucine, or valine) catalyzed with lipase from Pseudomonas fluorescens were determined. Unlike models of enzymic hydrolysis that neglect the thickness of the substrate monolayer, our method allows the determination of kinetic parameters in standard dimensions. The values of kcat for the synthetic pseudoglycerides were found to be significantly higher than that for trilaurin, while the values of Km(app) were close. This may be due to the presence of positively charged primary amino groups in the molecules of pseudoglycerides.     

The hydrolysis of new lipid-like substrates and trilaurin in monolayers catalyzed with the lipase fromPseudomonas fluorescens

A simple method for determining the enzymic hydrolysis parameters of lipid-like substrates and trilaurin assembled in monolayers at the water-air interface was suggested. At a surface pressure of 10 mN/m, the initial rates of lipolysis were found to be proportional to the decrease in area of the substrate monolayer caused by the enzymic hydrolysis in a single-compartment Langmuir balance. The kinetic parameters for the hydrolysis of trilaurin and three 1,3-dilaurylpseudoglycerides acetylated in position 2 with an amino acid (phenylalanine, leucine, or valine) catalyzed with lipase fromPseudomonas fluorescens were determined. Unlike models of enzymic hydrolysis that neglect the thickness of the substrate monolayer, our method allows the determination of kinetic parameters in standard dimensions. The values ofk _cat for the synthetic pseudoglycerides were found to be significantly higher than that for trilaurin, while the values ofK _m(app) were close. This may be due to the presence of positively charged primary amino groups in the molecules of pseudoglycerides.     

Silicon compounds as substrates and inhibitors of acetylcholinesterase

Several trimethylsilyl derivatives were found to be ligands of acetylcholinesterase (acetylcholine acetylhydrolase, EC 3.1.1.7): trimethylsilylethyl acetate (III) and trimethylsilylmethyl acetate (V) are substrates of the enzyme, whereas trimethylsilylethanol (VIII) is a competitive inhibitor. The silicon compounds have kinetic parameters similar to those of their carbon analogues, except for trimethylsilylmethyl acetate, which is a substrate of acetylcholinesterase, whereas its carbon analogue is not susceptible to enzymic hydrolysis.     

Kinetic parameters from progress curves of competing substrates. Application to beta-lactamases.

The use of two substrates, one of them a reporter substrate, is often convenient. The time course of an enzymic reaction with competing substrates is given explicitly in the present paper. Kinetic parameters can be readily obtained. The method is applied to the hydrolysis of benzylpenicillin, with cephalosporin C as the reporter substrate, catalysed by a Pseudomonas beta-lactamase.     

Thionesters as a probe for electrophilic catalysis in the serine protease mechanism

Specific and nonspecific thionester substrates for alpha-chymotrypsin and subtilisin Carlsberg have been synthesized and the kinetic parameters for their enzyme-catalyzed hydrolyses measured. Despite equal nonenzymic reactivities of ester-thionester pairs, each thionester is considerably less reactive toward enzymic hydrolysis, the difference being greatest for the specific substrates. The data support the operation of electrophilic catalysis by a hydrogen bond network at the carbonyl oxygen adjacent to the scissile bond of the substrate. The free energy of stabilization is 19 kJ mol-1 for a specific thionester substrate and will be higher for oxygen esters and amides. Chymotrypsin binds esters and thionesters about equally well, whereas subtilisin binds thionesters more tightly. This is consistent with continuous hydrogen bonding in the chymotrypsin mechanism and with a differential hydrogen bonding mechanism for subtilisin. A comparison of the relative rates of enzyme-catalyzed hydrolysis of ester and thionester substrates with their relative reactivities toward amines does not support an acyl histidine intermediate in the serine protease mechanism.     

Phytase from Wheat Bran

myo-Inositol mono-, di-, tri-, tetra-, and pentaphosphate were prepared by enzymic hydrolysis of myo-inositol hexaphosphate with a 1,500-fold purified phytase preparation from wheat bran and the subsequent Dowex 1 column chromatography. Relative initial rates of hydrolysis of these inositol phosphates by phytase were nearly the same each other and the activation energy of hydrolysis was about 11,000 cal. per mole for all these substrates. Km values did not vary widely with the substrates. The hydrolysis of inositol phosphates proceeded in a complicated way, except inositol monophosphate, where the reaction was of the first order. The enzyme hydrolyzed the substrates in the manner that removed phosphate group of them one by one. When mixed substrate was used the enzyme showed a preferential attack on the highest member of the phosphates present. From the mixed substrate test, it was concluded that wheat bran phytase is a single enzyme.     

Mechanism of action of dialkylaminoethylthiol derivatives of pyrimidine and quinazoline

A study was made of acute toxicity and radioprotective efficiency of some heterocyclic isothiuronium analogues and their ability to change the oxygen uptake by the organism. The rate of hydrolysis of the preparations in vitro was determined. A correlation was found between the above-mentioned indices. On the basis of the data obtained it was concluded that aminothiol, formed as the result of enzymic digestion in the organism, was responsible for the radioprotective effect of the compounds under study since it reduced the oxygen uptake by the organism.     

Kinetics of enzymic hydrolysis of malto-oligosaccharides: A comparison with acid hydrolysis

The hydrolysis of malto-oligosaccharides G₃-G₆ catalysed by porcine pancreatic alpha-amylase was investigated kinetically at 25°. Kinetic parameters corresponding to different positions of enzymic attack were determined and product inhibition was evaluated. The enzymic hydrolysis was compared in terms of reaction rate and pattern of action with hydrolysis in 0.1m H₂SO₄ at 70°. Mathematical models for the mechanism of hydrolysis were developed and a good rationalisation of the experimental results was achieved.     

Enzymic mechanisms involving concomitant transfer and hydrolysis reactions

The kinetic parameters of ten different enzymic mechanisms in which bimolecular transfer reactions occur concomitantly with the hydrolysis of the donor molecule have been studied. The usefulness of these parameters for making a choice of mechanism is discussed. The analysis has been extended to the use of alternative substrates in bimolecular transfer reactions that proceed without the hydrolysis of the donor molecule.     

Characteristics of substrate hydrolysis by endopeptidases from the hepatopancreas of the king crab

Kinetic parameters of hydrolysis of peptide and protein substrates by psychrophilic endopeptidases from hepatopancreas of the king crab Paralithodes camtschaticus (PC), in particular, by trypsin, collagenolytic protease, and metalloprotease, were measured at different temperatures. The PC trypsin was shown to hydrolyze Bz-Arg-pNA in the temperature range studied (4-37 degrees C) 19 times more effectively than bovine trypsin. The rate constants of hydrolysis of Glp-Ala-Ala-Leu-pNA by the PC collagenolytic protease increased approximately by one order of magnitude along with temperature decrease, while Km decreased by 3.5 times. The effective values of Km for the hydrolysis of azocasein by the metalloprotease insignificantly depend on temperature. We proposed that electrostatic interactions of negative charges around the cavity of active site are critical for the effective hydrolysis of substrates by endopeptidases of the PC hepatopancreas.     

Action of beta-galactosidase on novel synthetic macromolecular substrates. A processive enzymic reaction controlled by coulombic interactions

Macromolecular beta-galactosidase substrates were prepared by attaching o-nitrophenyl-beta-galactoside to carboxymethyldextran with positively charged linking groups. Almost all of the substituents were susceptible to enzymic hydrolysis by two distinct pathways. Under some conditions, there was random reaction to give a soluble product. In other conditions, in the initial stages of the reaction, most of the substituents of some, but not all, of the substrate polymers were hydrolyzed to give a product which precipitated as a second aqueous phase. Kinetics of hydrolysis were studied with respect to charge and molecular weight of both the enzyme and substrate. Factors that caused a decrease in Km favored formation of the second phase product. The reaction has similarities to the processive catalytic reactions found in naturally occurring enzyme systems with polymeric charged substrates.     

[3H]Indole-3-Acetyl-myo-Inositol Hydrolysis by Extracts of Zea mays L. Vegetative Tissue

[³H]Indole-3-acetyl-myo-inositol was hydrolyzed by buffered extracts of acetone powders prepared from 4 day shoots of dark grown Zea mays L. seedlings. The hydrolytic activity was proportional to the amount of extract added and was linear for up to 6 hours at 37°C. Boiled or alcohol denatured extracts were inactive. Analysis of reaction mixtures by high performance liquid chromatography demonstrated that not all isomers of indole-3-acetyl-myo-inositol were hydrolyzed at the same rate. Buffered extracts of acetone powders were prepared from coleoptiles and mesocotyls. The rates of hydrolysis observed with coleoptile extracts were greater than those observed with mesocotyl extracts. Active extracts also catalyzed the hydrolysis of esterase substrates such as α-naphthyl acetate and the methyl esters of indoleacetic acid and naphthyleneacetic acid. Attempts to purify the indole-3-acetyl-myo-inositol hydrolyzing activity by chromatographic procedures resulted in only slight purification with large losses of activity. Chromatography over hydroxylapatite allowed separation of two enzymically active fractions, one of which catalyzed the hydrolysis of both indole-3-acetyl-myo-inositol and esterase substrates. With the other fraction enzymic hydrolysis of esterase substrates was readily demonstrated, but no hydrolysis of indole-3-acetyl-myo-inositol was ever detected.     

The influence of glucose and ethanol on enzymic hydrolysis of steam-exploded bagasse

summary The rate of enzymic hydrolysis of steam-exploded bagasse was found to decrease linearly with increasing concentration of glucose and ethanol, with complete cessation of reaction predicted in the presence effects of glucose and ethanol were found to be additive. The significantly greater tolerance of the enzyme to ethanol can be utilised in the simultaneous hydrolysis and fermentation of bagasse cellulose to improve hydrolysis rate.     

The acid and enzymic hydrolysis of O-acetylated sialic acid residues from rabbit Tamm–Horsfall glycoprotein

Rabbit Tamm-Horsfall glycoprotein and bovine submaxillary glycoprotein were both found to contain sialic acid residues which are released at a slow rate by the standard conditions of acid hydrolysis. These residues are also resistant to neuraminidases from Vibrio cholerae and Clostridium perfringens. This behaviour was attributed to the presence of O-acetylated sialic acid, since the removal of O-acetyl groups by mild alkaline treatment normalized the subsequent release of sialic acid from rabbit Tamm-Horsfall glycoprotein by acid and by enzymic hydrolysis. Determination of the O-acetyl residues in rabbit Tamm-Horsfall glycoprotein indicated that on average two hydroxyl groups of sialic acid are O-acetylated, and these were located on the polyhydroxy side-chain of sialic acid or on C-4 and C-8. These findings confirm the assumption that certain O-acetylated forms of sialic acid are not substrates for bacterial neuraminidases. Several explanations have been suggested to explain the effect of O-acetylation of the side-chain on the rate of acidcatalysed hydrolysis of sialic acid residues.     

Comparison of the N-acetylhexosaminidase components in the ram testis and epididymis by isoelectric focusing

1. Several enzymic components, with both N-acetyl-beta-glucosaminidase and N-acetyl-beta-galactosaminidase activity, have been demonstrated in the ram testis and epididymis by isoelectric focusing. 2. The component (I), which predominates in the testis and caput of the epididymis, is isoelectric at pH6.2+/-0.1, whereas the predominant component (II) in the epididymal isthmus and cauda is isoelectric at pH7.0+/-0.1. 3. The total activity and the relative proportions of the enzymic components vary in the different sections of the epididymis. 4. Although their pH optima are slightly different, the appropriate K(m) values for components I and II for the hydrolysis of 4-methylumbelliferyl-N-acetyl-beta-glucosaminide and N-acetyl-beta-galactosaminide and the ratios of the maximal velocities towards the two substrates are very similar.     

Rat small-intestinal β-galactosidases. Kinetic studies with three separated fractions

1. Three fractions of beta-galactosidase activity from the rat small-intestinal mucosa were separated chromatographically. Two of these fractions had an acid pH optimum at 3-4, and the third one had a more neutral pH optimum at 5.7. 2. The two ;acid' beta-galactosidase fractions had considerably lower K(m) values for hetero beta-galactosides than for lactose. The V(max.) values were similar for all the substrates used (lactose, phenyl beta-galactoside, o-nitrophenyl beta-galactoside, p-nitrophenyl beta-galactoside and 6-bromo-2-naphthyl beta-galactoside). No difference could be detected between the two ;acid' fractions with respect to their enzymic properties (pH optimum, K(m) for the different substrates, K(i) for lactose as an inhibitor of the hydrolysis of hetero beta-galactosides, K(i) for phenyl beta-galactoside as an inhibitor of the hydrolysis of lactose, and relative V(max.) for the hydrolysis of different substrates). These two fractions probably represent different forms of the same enzyme. 3. The ;neutral' fraction had similar K(m) values for all the substrates hydrolysed, but with lactose as substrate the V(max.) was much higher than with the hetero beta-galactosides. This fraction did not split phenyl beta-galactoside or 6-bromo-2-naphthyl beta-galactoside at a measurable rate. 4. Lactose was a competitive inhibitor of the hetero beta-galactosidase activities of all the three fractions, and K(i) for lactose as an inhibitor in each case was the same as K(m) for the lactase activity. Phenyl beta-galactoside was a competitive inhibitor of the lactase activity of all the three fractions. These facts strongly indicate that in all the three fractions lactose is hydrolysed by the same active sites as the hetero beta-galactosides. 5. Human serum albumin stabilized the separated enzymes against inactivation by freezing and thawing.     

Lipase-mediated hydrolysis of blackcurrant oil

Four commercially available lipases, both free and immobilized, were tested for their ability to catalyze hydrolysis of blackcurrant (Ribes nigrum) oil using two different approaches. The lipase from Mucor miehei was studied free and immobilized in two different ways. The former series of enzymic reactions were performed in tap water at 40 degrees C, but the latter series of enzymic processes were carried out in mixtures of isooctane and phosphate buffer (in a typical 2/1 ratio of the components) at 30 degrees C. These conditions were optimized to increase and/or to maximize the yields of the products, which were priority targets in this study. A rate of hydrolysis and a selective preference of the hydrolytic enzymes towards fatty acids, with a special focus on enrichment of alpha-linolenic acid and/or gamma-linolenic acid, were studied. Higher rates of hydrolysis of the blackcurrant oil in the former series of reactions were observed with the immobilized lipase from Pseudomonas cepacia used as biocatalyst. In the latter approach, the most favorable results of the rate of hydrolysis of the target blackcurrant oil were achieved with the immobilized lipase from Mucor miehei employed as biocatalyst. Only three lipases, selected from a series of lipases tested during this investigation, displayed specificity towards alpha-linolenic acid and gamma-linolenic acid, i.e. the immobilized lipase from P. cepacia, lipase from M. miehei and lipase from P. fluorescens.