Crude aminoacylase from aspergillus sp. is a mixture of hydrolases

A range of cross-linked enzyme aggregates (CLEAs) was prepared from commercially available aminoacylase I. Results from three test reactions showed that aminoacylase does not possess aminolysis or alcoholysis activity, both previously ascribed to this enzyme. This result was confirmed using aminoacylase purified by chromatographic techniques, which leads us to conclude that the previously observed acylations of esters and amines is due to other enzymes present as impurities in the crude aminoacylase I.     

Further characterization of porcine kidney aminoacylase I reveals close similarity to 'renal dipeptidase'

We present data indicating that aminoacylase I (EC 3.5.1.14) from porcine kidney and 'renal dipeptidase' (EC 3.4.13.11) are closely related. We show that, in situ, a considerable fraction of aminoacylase activity ist attached to membranes. Incubation of washed microsomal membranes with phospholipase C from B. cereus results in the rapid solubilization of aminoacylase I, suggesting that aminoacylase--as shown for renal dipeptidase before--bears a glycolipid 'membrane anchor'. In agreement with this assumption, purified aminoacylase was found to contain myo-inositol, a characteristic component of phosphatidylinositol-anchored membrane proteins. A reexamination of the molecular mass of purified aminoacylase yielded values (46,000 +/- 2,000 Da by SDS polyacrylamide electrophoresis, 98,000 +/- 5,000 Da by sedimentation equilibrium centrifugation) similar to those reported for renal dipeptidase. The enzymes coelute during most of the procedures applied in the purification of aminoacylase or renal dipeptidase, but can be separated by hydrophobic interaction chromatography. A survey of the literature revealed a series of additional features of aminoacylase I and renal dipeptidase (amino-acid composition, isoelectric points, metal dependence, and more) that are strikingly similar.     

Aminoacylase I deficiency: a novel inborn error of metabolism

This is the first report of a patient with aminoacylase I deficiency. High amounts of N-acetylated amino acids were detected by gas chromatography-mass spectrometry in the urine, including the derivatives of serine, glutamic acid, alanine, methionine, glycine, and smaller amounts of threonine, leucine, valine, and isoleucine. NMR spectroscopy confirmed these findings and, in addition, showed the presence of N-acetylglutamine and N-acetylasparagine. In EBV transformed lymphoblasts, aminoacylase I activity was deficient. Loss of activity was due to decreased amounts of aminoacylase I protein. The amount of mRNA for the aminoacylase I was decreased. DNA sequencing of the encoding ACY1 gene showed a homozygous c.1057 C>T transition, predicting a p.Arg353Cys substitution. Both parents were heterozygous for the mutation. The mutation was also detected in 5/161 controls. To exclude the possibility of a genetic polymorphism, protein expression studies were performed showing that the mutant protein had lost catalytic activity.     

Aminoacylase I is not a glycolipid-anchored ectoenzyme in pig kidney.

Subcellular fractionation of pig kidney cortex revealed that aminoacylase I (EC 3.5.1.14, N-acyl-L-amino-acid aminohydrolase) is predominantly a soluble enzyme with only 0.5% of the total activity being recovered in the membrane fraction. The aminoacylase I activity associated with the membrane preparations displayed neither rapid release following incubation with phosphatidylinositol-specific phospholipase C from Bacillus thuringiensis nor the distinctive differential pattern of detergent solubilization which was seen with glycosyl-phosphatidylinositol-anchored proteins (renal dipeptidase, alkaline phosphatase). When fractionated by phase separation in Triton X-114, integral membrane proteins of kidney microvillar membranes partitioned predominantly (greater than 90%) into the detergent-rich phase. In contrast, only 3.7% of aminoacylase I activity associated with microvillar membranes partitioned into the detergent-rich phase. Aminoacylase I activity of pig kidney would therefore appear to be a hydrophilic protein in nature and is not, as suggested previously, a G-PI-anchored integral membrane protein.     

Nuclear magnetic relaxation studies of the role of the metal ion in Mn2(+)-substituted aminoacylase I

Substitution of the essential Zn2+ ions of porcine kidney aminoacylase I (EC 3.5.1.14) by Mn2+ did not markedly affect the kinetic properties of the enzyme. Using Mn2+ as a paramagnetic probe, we were able to study the conformations of bound ligands by measuring the enhancement of ligand proton relaxation in 1H NMR. In addition, the effects of inhibitors on the paramagnetic enhancement of water proton relaxation rates were examined. The results of both approaches, in agreement with kinetic evidence, suggest that the metal center of aminoacylase I is too distant from the ligand binding site to allow direct participation of the metal in substrate binding or catalysis. We, therefore, propose that the metal ion of aminoacylase I plays a purely structural role.     

Catalysis by hog-kidney aminoacylase does not involve a covalent intermediate

Hog kidney aminoacylase (N-acylamino acid amidohydrolase; acylase I) is shown to catalyze the exchange of acetate oxygens with water at a significant rate only when alanine is present simultaneously. These studies, conducted using the 18O-isotope induced shift on 13C-NMR spectra, provide evidence in favor of a linear kinetic mechanism as opposed to a 'ping-pong' double-displacement mechanism. At pH values above neutrality, aminoacylase I also catalyzes the exchange of alanine oxygens with those of water. Ionic strength and pH effects on the kinetics of aminoacylase I are examined and the results are interpreted in terms of a model of the enzyme active site.     

Gene cloning, sequence analysis, purification, and characterization of a thermostable aminoacylase from Bacillus stearothermophilus.

A genomic DNA fragment encoding aminoacylase activity of the eubacterium Bacillus stearothermophilus was cloned into Escherichia coli. Transformants expressing aminoacylase activity were selected by their ability to complement E. coli mutants defective in acetylornithine deacetylase activity, the enzyme that converts N-acetylornithine to ornithine in the arginine biosynthetic pathway. The 2.3-kb cloned fragment has been entirely sequenced. Analysis of the sequence revealed two open reading frames, one of which encoded the aminoacylase. B. stearothermophilus aminoacylase, produced in E. coli, was purified to near homogeneity in three steps, one of which took advantage of the intrinsic thermostability of the enzyme. The enzyme exists as homotetramer of 43-kDa subunits as shown by cross-linking experiments. The deacetylating capacity of purified aminoacylase varies considerably depending on the nature of the amino acid residue in the substrate. The enzyme hydrolyzes N-acyl derivatives of aromatic amino acids most efficiently. Comparison of the predicted amino acid sequence of B. stearothermophilus aminoacylase with those of eubacterial acetylornithine deacylase, succinyldiaminopimelate desuccinylase, carboxypeptidase G2, and eukaryotic aminoacylase I suggests a common origin for these enzymes.     

氨基酰化酶Ⅰ的必需半胱氨酸巯基

本文用DTNB和IAM修饰了猪肾氨基酰化酶Ⅰ的半胱氨酸巯基,用Koshland和邹承鲁作图法定量处理的结果都表明,酶分子中有二个巯基为酶的必需巯基。     

An improved method for determination of N-acetyl-L-glutamate by its function as an activator of carbamoyl phosphate synthetase I

N-Acetyl-L-glutamate has been examined with regard to its ability to activate carbamoyl phosphate synthetase I (EC 6.3.4.16). Substance(s) inhibitory to carbamoyl phosphate synthetase, present even in the partially purified preparation of rat liver extracts, interfered with the measurement of acetylglutamate. In the experiments using chelating agents, metals were apparently involved in this inhibition. When the partially purified preparation of liver extract was placed on a Chelex 100 column, the inhibitor was eliminated and accurate measurements of acetylglutamate content could be made. Evidence supporting the validity of this improved method is given. A significant difference was observed between acetylglutamate levels determined by the present method and by the one using aminoacylase I (N-acylamino acid amidohydrolase, EC 3.5.1.14) to hydrolyze acetylglutamate followed by assay of the glutamate generated. We searched for the presence of glutamate derivatives other than acetylglutamate. When impure tissue preparations containing acetylglutamate were treated with a commercial preparation of aminoacylase, there was an excess amount of glutamate apparently derived from compounds other than acetylglutamate. This can lead to an overestimation of the tissue levels of acetylglutamate.     

Reactivities of sulfhydryl groups in native and metal-free aminoacylase I

Aminoacylase I from porcine kidney (EC 3.5.1.14) contains seven cysteine residues per subunit. Three sulfhydryl groups are accessible to modification by 4-hydroxymercuribenzoate (p-MB). The kinetics of the reaction suggest that only one of these groups affects acylase activity when modified by p-MB. Its reaction rate increases 2-3-fold when the essential metal ion of aminoacylase is removed. Modification of metal-free apoenzyme by N-ethylmaleimide (NEM) abolishes its activity without impairing Zn2+ binding. This indicates that the sulfhydryl group reacting with NEM is not directly coordinated to the metal. DTNB (5,5'-Dithio-bis(2-nitrobenzoate), Ellman's reagent) also modifies three sulfhydryl groups per subunit. In this case, the reactivities of native aminoacylase and apoenzyme are not significantly different. N-Hydroxy-2-aminobutyrate, a strong aminoacylase inhibitor, substantially increases the reactivity of the slowest reacting sulfhydryl in both native enzyme and metal-free aminoacylase. It appears that binding of the inhibitor or removal of the metal ion induces conformational changes of the amino-acylase active site that render a buried sulfhydryl group more accessible to modification.     

Isolation and characterization of N-long chain acyl aminoacylase from Pseudomonas diminuta

N-Long chain acyl aminoacylase II (Enzyme II) catalyzing the hydrolysis of N-long chain acyl amino acids was purified about 2,000-fold from the cell extracts of Pseudomonas diminuta with 1.8% of activity yield. The purified enzyme was homogeneous on polyacrylamide gel electrophoresis and the molecular weight was 220,000. Enzyme II differed from N-long chain acyl aminoacylase I (Enzyme I) in molecular weight, in substrate specificity, and in behavior toward temperature and pH. Enzyme II showed broader substrate specificity than Enzyme I and catalyzed the hydrolysis of lipoamino acids containing various amino acid residues, although Enzyme I was almost specific to the lipoamino acids containing L-glutamate. The extent of hydrolysis by Enzyme II reaction varied depending on the kinds of lipoamino acids and were: 100% for palmitoyl-L-glutamate, 91% for myristoyl-L-glutamate, 85% for lauroyl-L-glutamate, 54% for lauroyl-L-aspartate, 28% for stearoyl-L-glutamate and 17.5% for lauroyl-glycine.     

Application of immobilized aminoacylase from Micrococcus agilis for isolation of D-phenylglycine from its racemic mixture

The procedure for isolation of D -phenylglycine from its racemic mixture by enzymatic hydrolysis of L -enantiomer of N-acetyl-D ,L -phenylglycine is described. For this hydrolysis. aminoacylase from Micrococcus agilis immobilized by sorption of DEAE-cellulose was applied. As is also shown, the course of enzymatic reaction can be directly controlled by spectrophotometric method.     

Aminoacylase pellets.

Aminoacylase was immobilized on the mycelium pellets of Aspergillus ochraceus by using albumin and glutaraldehyde. No difference in the optimum pH was observed between native aminoacylase and aminoacylase pellets. The aminoacylase pellets were stable in pH 4-8 but they were unstable in alkaline conditions. The aminoacylase pellets were more stable against heavy metal ions and inhibitors than native aminoacylase. However, the degree of the activation of aminoacylase with cobalt ion decreased with the immobilization. It was suggested that most of aminoacylase was covalently coupled to the mycelium with glutaraldehyde.     

The molecular basis of aminoacylase 1 deficiency

Aminoacylase 1 is a zinc-binding enzyme which hydrolyzes N-acetyl amino acids into the free amino acid and acetic acid. Deficiency of aminoacylase 1 due to mutations in the aminoacylase 1 (ACY1) gene follows an autosomal-recessive trait of inheritance and is characterized by accumulation of N-acetyl amino acids in the urine. In affected individuals neurological findings such as febrile seizures, delay of psychomotor development and moderate mental retardation have been reported. Except for one missense mutation which has been studied in Escherichia coli, mutations underlying aminoacylase 1 deficiency have not been characterized so far. This has prompted us to approach expression studies of all mutations known to occur in aminoacylase 1 deficient individuals in a human cell line (HEK293), thus providing the authentic human machinery for posttranslational modifications. Mutations were inserted using site directed mutagenesis and aminoacylase 1 enzyme activity was assessed in cells overexpressing aminoacylase 1, using mainly the natural high affinity substrate N-acetyl methionine. Overexpression of the wild type enzyme in HEK293 cells resulted in an approximately 50-fold increase of the aminoacylase 1 activity of homogenized cells. Most mutations resulted in a nearly complete loss of enzyme function. Notably, the two newly discovered mutations p.Arg378Trp, p.Arg378Gln and the mutation p.Arg393His yielded considerable residual activity of the enzyme, which is tentatively explained by their intramolecular localization and molecular characteristics. In contrast to aminoacylase 1 variants which showed no detectable aminoacylase 1 activity, aminoacylase 1 proteins with the mutations p.Arg378Trp, p.Arg378Gln and p.Arg393His were also detected in Western blot analysis. Investigations of the molecular bases of additional cases of aminoacylase 1 deficiency contribute to a better understanding of this inborn error of metabolism whose clinical significance and long-term consequences remain to be elucidated.     

Butylmalonate is a transition state analogue for aminocylase I

Butylmalonate (butyl propanedioic acid) is a slow-binding inhibitor of porcine renal aminoacylase I (EC 3.5.1.14), causing transients of activity with half-times of more than 10 min. At 25°C and pH 7.0, the dissociation rate of the complex is approximately 6 × 10⁻⁴ s⁻¹, while the rate constant of complex formation is in the order of 20 M⁻¹·s⁻¹. In good agreement with these data, steady-state kinetics yield an estimated inhibition constant around 100 μM. Molecular mechanics calculations showed that conformation and charge distribution of butylmalonate are strikingly similar to those of the putative transition state of aminoacylase catalysis.     

Immobilized Aminoacylase on Porous Glass Beads

The preparation and properties of immobilized aminoacylase on porous glass by covalent binding [Porous glass-CVB-aminoacylase] and the continuous enzymatic reactions using such preparations are described.

Two types of porous glass-CVB-aminoacylase were prepared. One was aminoacylase covalently bound to alkylaminosilane derivative of porous glass with glutaraldehyde as a coupling agent [Alkylamino-porous glass-CVB-aminoacylase], and the other was aminoacylase covalently bound to arylaminosilane derivative of porous glass with nitrous acid as a coupling agent [Arylamino-porous glass-CVB-aminoacylase]. The enzyme activities of such immobilized aminoacylases were 3.2~13.0 units/ml glass for the former and 1.9~6.8 units/ml glass for the latter. Especially, alkylamino porous glass-CVB-aminoacylase showed excellent stability at pH 6~9 and temperature below 50°C, and was able to be stored for more than six months without appreciable loss of the activity.

The continuous enzyme reaction using the alkylamino porous glass-CVB-aminoacylase packed in a column was operated for 54 days at 37°C, and the half-life of the immobilized enzyme was calculated to be 78 days. From these results, it was recognized that such an immobilized aminoacylase on porous glass would be applicable in an industrial preparation of various l-amino acids from their dl-forms.     

Role of osmolytes as chemical chaperones during the refolding of aminoacylase.

The refolding and reactivation of aminoacylase is particularly difficult because of serious off-pathway aggregation. The effects of 4 osmolytes--dimethylsulphoxide, glycerol, proline, and sucrose--on the refolding and reactivation of guanidine-denatured aminoacylase were studied by measuring aggregation, enzyme activity, intrinsic fluorescence spectra, 1-anilino-8-naphthalenesulfonate (ANS) fluorescence spectra, and circular dichroism (CD) spectra. The results show that all the osmolytes not only inhibit aggregation but also recover the activity of aminoacylase during refolding in a concentration-dependent manner. In particularly, a 40% glycerol concentration and a 1.5 mol/L sucrose concentration almost completely suppressed the aminoacylase aggregation. The enzyme activity measurements revealed that the influence of glycerol is more significant than that of any other osmolyte. The intrinsic fluorescence results showed that glycerol, proline, and sucrose stabilized the aminoacylase conformation effectively, with glycerol being the most effective. All 4 kinds of osmolytes reduced the exposure of the hydrophobic surface, indicating that osmolytes facilitate the formation of protein hydrophobic collapse. The CD results indicate that glycerol and sucrose facilitate the return of aminoacylase to its native secondary structure. The results of this study suggest that the ability of the various osmolytes to facilitate the refolding and renaturation of aminoacylase is not the same. A survey of the results in the literature, as well as those presented here, suggests that although the protective effect of osmolytes on protein activity and structure is equal for different osmolytes, the ability of osmolytes to facilitate the refolding of various proteins differs from case to case. In all cases, glycerol was found to be the best stabilizer and a folding aid.     

Trichloroacetic acid-induced molten globule state of aminoacylase from pig kidney

The trichloroacetic acid (TCA)-induced unfolding of aminoacylase was investigated by measurement of aggregation, enzyme activity, intrinsic fluorescence, 8-anilino-1-naphthalene sulfonate (ANS) binding, circular dichroism, and native polyacrylamide gel electrophoresis. The results showed that TCA caused inactivation and unfolding of aminoacylase. Intrinsic fluorescence results demonstrated that the TCA-induced transition of aminoacylase was characterized by two distinct stages during which the fluorescence emission maxima first redshifted to 338 nm and then blueshifted to 332 nm, close to that of native protein. ANS binding measurements revealed that TCA-denatured aminoacylase had a large hydrophobic area for TCA concentration near 2 mM. Comparison of the relative changes in wavelength shift and in the ANS intensity suggested the formation of a stable molten globule state of aminoacylase with a slightly disrupted tertiary structure and more hydrophobic surface than the native protein. Far-UV circular dichroism results provided further support that TCA induced the formation of two partially folded intermediates each with an enhanced native-like secondary structure. The results collectively suggest that a TCA-induced molten globule state is formed and stabilized during unfolding of aminoacylase and that association of the molten globule state may account for precipitation of the protein when denatured by TCA.     

Properties of acylase preparations from an actinomycete culture

A comparative study of some physico-chemical properties of high-purified preparations of extracellular penicillin-V-acylase and aminoacylase, isolated from the actinomycete Streptoverticillium No 62, revealed the difference in pH and temperature optima, in the sensitivity to the ionic composition of buffer solutions, in the enzyme stability during storage. As for the aminoacylase preparation, its thermostability was studied at different pH values, as well as the effect of specific compounds was tested. Similar to other fungal enzymes, the aminoacylase possesses a wide substrate specificity, and by its stereospecificity can be related to L-aminoacylases, while penicillin-V-acylase is a high-specific enzyme, active against phenoxymethylpenicillin.