Bacteriolytic enzymes from Staphylococcus aureus. Specificity of ction of endo-beta-N-acetylglucosaminidase

CFTR dysfunction leads to defective bacterial eradication on cystic fibrosis airways

Dysfunction of the cystic fibrosis transmembrane conductance regulator (CFTR) anion channel by genetic mutations causes the inherited disease cystic fibrosis (CF). CF lung disease that involves multiple disorders of epithelial function likely results from loss of CFTR function as an anion channel conducting chloride and bicarbonate ions and its function as a cellular regulator modulating the activity of membrane and cytosol proteins. In the absence of CFTR activity, abundant mucus accumulation, bacterial infection and inflammation characterize CF airways, in which inflammation-associated tissue remodeling and damage gradually destroys the lung. Deciphering the link between CFTR dysfunction and bacterial infection in CF airways may reveal the pathogenesis of CF lung disease and guide the development of new treatments. Research efforts towards this goal, including high salt, low volume, airway surface liquid acidosis and abnormal mucus hypotheses are critically reviewed.

Impaired respiration elicits SrrAB-dependent programmed cell lysis and biofilm formation in Staphylococcus aureus

Biofilms are communities of microorganisms attached to a surface or each other. Biofilm-associated cells are the etiologic agents of recurrent Staphylococcus aureus infections. Infected human tissues are hypoxic or anoxic. S. aureus increases biofilm formation in response to hypoxia, but how this occurs is unknown. In the current study we report that oxygen influences biofilm formation in its capacity as a terminal electron acceptor for cellular respiration. Genetic, physiological, or chemical inhibition of respiratory processes elicited increased biofilm formation. Impaired respiration led to increased cell lysis via divergent regulation of two processes: increased expression of the AtlA murein hydrolase and decreased expression of wall-teichoic acids. The AltA-dependent release of cytosolic DNA contributed to increased biofilm formation. Further, cell lysis and biofilm formation were governed by the SrrAB two-component regulatory system. Data presented support a model wherein SrrAB-dependent biofilm formation occurs in response to the accumulation of reduced menaquinone.

DOI:http://dx.doi.org/10.7554/eLife.23845.001

Millions of bacteria live on the human body. Generally these bacteria co-exist with us peacefully, but sometimes certain bacteria may enter the body and cause infections, such as gum disease or a bone infection called osteomyelitis. Many of these infections are thought to occur when the bacteria become able to form complex communities called biofilms. Bacteria living in a biofilm cooperate and make lifestyle choices as a community, so in this way, they behave like a single organism containing many cells.

A sticky glue-like material called the matrix holds the bacteria in a biofilm together. This matrix protects the bacteria in the biofilm from both the human immune system and antibiotics, allowing infections to develop and making them difficult to treat.

Previous research has shown that the supply and level of oxygen in infected tissues decreases as an infection gets worse. One bacterium that typically lives peacefully on our bodies, called Staphylococcus aureus, can sometimes cause serious biofilm-associated infections. S. aureus forms biofilms more readily when oxygen is in short supply, but it was not known how these biofilms form. Understanding how S. aureus forms biofilms could help scientists develop better treatments for bacterial infections.

Most bacterial cells have a cell wall to provide them with structural support. Mashruwala et al. found that, when oxygen levels are low, S. aureus decreases the production of a type of sugar that makes up the cell wall. At the same time, the bacteria produce more of an enzyme that breaks down cell walls. Together, these processes cause some of the bacteria cells to break open. The contents of these broken cells, including their DNA, help form the matrix that will hold together and protect the other bacterial cells in the biofilm. The experiments also identified a protein called SrrAB that switches on the process that ruptures the cells when oxygen is low.

The findings of Mashruwala et al. show how bacteria grown in the laboratory form biofilms when they are starved of oxygen. The next steps following on from this work are to find out whether the same thing happens when bacteria infect animals and whether drugs that block the rupturing of bacterial cells could be used to treat infections.

DOI:http://dx.doi.org/10.7554/eLife.23845.002

SagB Glucosaminidase Is a Determinant of Staphylococcus aureus Glycan Chain Length, Antibiotic Susceptibility, and Protein Secretion

The envelope of Staphylococcus aureus is comprised of peptidoglycan and its attached secondary polymers, teichoic acid, capsular polysaccharide, and protein. Peptidoglycan synthesis involves polymerization of lipid II precursors into glycan strands that are cross-linked at wall peptides. It is not clear whether peptidoglycan structure is principally determined during polymerization or whether processive enzymes affect cell wall structure and function, for example, by generating conduits for protein secretion. We show here that S. aureus lacking SagB, a membrane-associated N-acetylglucosaminidase, displays growth and cell-morphological defects caused by the exaggerated length of peptidoglycan strands. SagB cleaves polymerized glycan strands to their physiological length and modulates antibiotic resistance in methicillin-resistant S. aureus (MRSA). Deletion of sagB perturbs protein trafficking into and across the envelope, conferring defects in cell wall anchoring and secretion, as well as aberrant excretion of cytoplasmic proteins.

IMPORTANCE

Staphylococcus aureus is thought to secrete proteins across the plasma membrane via the Sec pathway; however, protein transport across the cell wall envelope has heretofore not been studied. We report that S. aureus sagB mutants generate elongated peptidoglycan strands and display defects in protein secretion as well as aberrant excretion of cytoplasmic proteins. These results suggest that the thick peptidoglycan layer of staphylococci presents a barrier for protein secretion and that SagB appears to extend the Sec pathway across the cell wall envelope.

msaABCR operon positively regulates biofilm development by repressing proteases and autolysis in Staphylococcus aureus

Staphylococcus aureus is an important human pathogen that causes nosocomial and community-acquired infections. One of the most important aspects of staphylococcal infections is biofilm development within the host, which renders the bacterium resistant to the host's immune response and antimicrobial agents. Biofilm development is very complex and involves several regulators that ensure cell survival on surfaces within the extracellular polymeric matrix. Previously, we identified the msaABCR operon as an additional positive regulator of biofilm formation. In this study, we define the regulatory pathway by which msaABCR controls biofilm formation. We demonstrate that the msaABCR operon is a negative regulator of proteases. The control of protease production mediates the processing of the major autolysin, Atl, and thus regulates the rate of autolysis. In the absence of the msaABCR operon, Atl is processed by proteases at a high rate, leading to increased cell death and a defect in biofilm maturation. We conclude that the msaABCR operon plays a key role in maintaining the balance between autolysis and growth within the staphylococcal biofilm.

Functional and structural analysis of the major amidase (Atl) in Staphylococcus

The cytoplasmic membrane of most bacteria is surrounded by a more or less thick murein layer (peptidoglycan) that protects the protoplast from mechanical damage, osmotic rupture and lysis. When bacteria are dividing processes are initiated stepwise that involve DNA replication, constriction of the membranes, cell growth, biosynthesis of new murein, and finally the generation of two daughter cells. As the daughter cells are still covalently interlinked by the murein network they must be separated by specific peptidoglycan hydrolases, also referred to as autolysins. In staphylococci, the major autolysin (Atl) and its processed products N-acetylmuramoyl-l-alanine amidase (AM) and endo-β-N-acetylglucosaminidase (GL) have been in the research focus for long time. This review addresses phenotypic consequences of atl mutants, impact of Atl in virulence, the mechanism of targeting to the septum region, regulation of atl, the structure of the amidase and the repeat regions, as well as the phylogeny of Atl and its use in Staphylococcus genus and species typing.

Contribution of the Staphylococcus aureus Atl AM and GL murein hydrolase activities in cell division, autolysis, and biofilm formation

The most prominent murein hydrolase of Staphylococcus aureus, AtlA, is a bifunctional enzyme that undergoes proteolytic cleavage to yield two catalytically active proteins, an amidase (AM) and a glucosaminidase (GL). Although the bifunctional nature of AtlA has long been recognized, most studies have focused on the combined functions of this protein in cell wall metabolism and biofilm development. In this study, we generated mutant derivatives of the clinical S. aureus isolate, UAMS-1, in which one or both of the AM and GL domains of AtlA have been deleted. Examination of these strains revealed that each mutant exhibited growth rates comparable to the parental strain, but showed clumping phenotypes and lysis profiles that were distinct from the parental strain and each other, suggesting distinct roles in cell wall metabolism. Given the known function of autolysis in the release of genomic DNA for use as a biofilm matrix molecule, we also tested the mutants in biofilm assays and found both AM and GL necessary for biofilm development. Furthermore, the use of enzymatically inactive point mutations revealed that both AM and GL must be catalytically active for S. aureus to form a biofilm. The results of this study provide insight into the relative contributions of AM and GL in S. aureus and demonstrate the contribution of Atl-mediated lysis in biofilm development.

Innate immunity in the respiratory epithelium

The airway epithelium represents the first point of contact for inhaled foreign organisms. The protective arsenal of the airway epithelium is provided in the form of physical barriers and a vast array of receptors and antimicrobial compounds that constitute the innate immune system. Many of the known innate immune receptors, including the Toll-like receptors and nucleotide oligomerization domain-like receptors, are expressed by the airway epithelium, which leads to the production of proinflammatory cytokines and chemokines that affect microorganisms directly and recruit immune cells, such as neutrophils and T cells, to the site of infection. The airway epithelium also produces a number of resident antimicrobial proteins, such as lysozyme, lactoferrin, and mucins, as well as a swathe of cationic proteins. Dysregulation of the airway epithelial innate immune system is associated with a number of medical conditions that can result in compromised immunity and chronic inflammation of the lung. This review focuses on the innate immune capabilities of the airway epithelium and its role in protecting the lung from infection as well as the outcomes when its function is compromised.

Cloning and expression of a Staphylococcus aureus gene encoding a peptidoglycan hydrolase activity

A gene of Staphylococcus aureus PS47 encoding lytic activity was cloned and expressed in Escherichia coli. Deletion analysis of a recombinant plasmid carrying a 7.4-kilobase-pair fragment (kbp) of S. aureus DNA suggested that the gene was located within a 2.5-kbp EcoRI-XbaI fragment. Analysis of extracts of E. coli harboring recombinant plasmids on denaturing polyacrylamide gels containing purified cell walls of S. aureus showed a clearing zone by a polypeptide of apparent Mr 23,000. The release of dinitrophenylalanine but not reducing groups from purified cell walls by a cell extract of recombinant E. coli suggested that we had cloned an N-acetylmuramyl-L-alanine amidase.

Purification and characterization of three separate bacteriolytic enzymes excreted by Staphylococcus aureus, Staphylococcus simulans, and Staphylococcus saprophyticus

As a further development of previous investigations showing that different staphylococcal species display different bacteriolytic activity patterns (lyogroups), the bacteriolytic enzymes excreted by three different Staphylococcus species, Staphylococcus aureus (lyogroup I), S. simulans (lyogroup II), and S. saprophyticus (lyogroup IV); have been purified and characterized. A representative strain from each species was grown in a preselected medium made of fully dialyzable products. Culture supernatants were collected in the appropriate growth phase. Two different affinity adsorbents were used for enzyme purification. One was obtained by coupling lysozyme-digested pure peptidoglycan from Micrococcus luteus to cyanogen bromide-activated Sepharose 4B. The second affinity adsorbent used was chitin. The S. aureus bacteriolytic enzyme bound to the solubilized peptidoglycan but not to chitin, whereas the opposite was true for the S. simulans enzyme. The bacteriolytic enzyme from S. saprophyticus did not bind to either the Sepharose 4B-peptidoglycan resin or to chitin, and its purification was achieved by two ion-exchange chromatography steps combined with gel filtration. All three enzymes were purified to apparent homogeneity. Their subsequent characterization indicated that all acted as endo-beta-N-acetylglucosaminidases. However, the three glucosaminidases differed significantly in their kinetics of activity and bacteriolytic spectrum against heat-killed cells of a variety of microorganisms. Very different values also resulted from molecular weight determinations: 80,000 for the S. aureus enzyme, 45,000 for the S. simulans enzyme, and 31,000 for the S. saprophyticus enzyme. Other important differences were observed in their stability, optimal pH and ionic strength for their activity, and their responses to temperature and divalent cations. These results confirmed the previous proposal that different staphylococcal species excrete different lytic enzymes.

Stimulation of spreading of trypsinized human fibroblasts by lysozymes from Staphylococcus aureus, hen egg white, and human urine

The effect of lysozyme from three different sources--Staphylococcus aureus, hen egg white, and human urine--on adhesion to substrate and spreading of trypsinized human fibroblasts was studied. Several fibroblast strains were tested under various conditions. It was found that the different cell strains did not show the same capability of spreading and stably attaching to substrates when resuspended in media not containing serum. Some strains did not spread, whereas others spread even in the absence of serum. Cell spreading in these strains did not occur when the cells were pregrown for 5 weeks in media supplemented with 1% fetal bovine serum. Lysozyme from S. aureus allowed stable adhesion to substrate and spreading of all the fibroblast strains unable to elongate in nonsupplemented minimal essential medium. This enzyme accelerated and augmented spreading of the strains capable of elongating in the absence of serum. S. aureus lysozyme also allowed spreading and stable adhesion to substrates of all these strains when they were pregrown for 5 weeks in the presence of 1% fetal bovine serum. Furthermore, hen egg white lysozyme and the lysozyme purified from human urine were both capable of stimulating anchorage to substrate and spreading of trypsinized fibroblasts although their effect was less pronounced than that of the S. aureus lysozyme. Some tentative hypotheses for the mechanism of cell spreading in the presence of lysozyme are made. The possibility that lysozymes, virtually ubiquitous enzymes, may play a specific role in nature in the regulation of cell differentiation and tissue development is finally raised and discussed in light of several previous observations and findings.

Specificity of bacteriolytic enzyme II from a soil amoeba, Hartmannella glebae

Two bacteriolytic enzymes were produced when Hartmanella glebae was grown in the presence of both Enterobacter aerogenes and Alcaligenes faecalis. The identification of enzyme I as N-acetylmuramidase was reported earlier. Enzyme II was purified by gel filtration on a Bio-Gel A column. A recovery of 68.76% with 72.3-fold purification was obtained. It was found that 5 and 10 mM MgCl2 significantly increased the bacteriolytic activity. It is a basic protein. The cell walls of Micrococcus lysodeikticus were lysed by the enzyme, and the products of digestion were purified by Amberlite CG-120 and Sephadex G-15 chromatography to facilitate the detection of amino sugars. After reduction of the oligosaccharides with sodium borohydride and acid hydrolysis, the amino sugars were identified by paper chromatography. It was found that enzyme II cleaved the glycosidic bond between N-acetylmuramic and and N-acetylglucosamine of the peptidoglycan moiety of the cell walls. Thus, the enzyme was identified as endo-beta-N-acetylmuramidase.

Purification and properties of beta-N-acetylhexosaminidase from the mollusc Helicella ericetorum Müller

1. A beta-N-acetylhexosaminidase was purified 330-fold from the digestive gland of the terrestrial mollusc Helicella ericetorum Müller. 2. Its pH optimum is 4.5 for both beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities in two buffer solutions; it is fully stable at 37 degrees C for 2h in the pH range 3.8--4.6 and shows one isoelectric point (pH 4.83). 3. The estimated mol.wt. is between 120,000 and 145,000. 4. The enzyme shows an endo-beta-N-acetylhexosaminidase activity on natural substrates such as ovalbumin, ovomucoid, chondroitin 4-sulphate, chitin and hyaluronic acid. 5. Two forms of the enzyme were separated by preparative polyacrylamide-gel electrophoresis. 6. Km and Vmax. for p-nitrophenyl 2-acetamido-2-deoxy-beta-D-glucopyranoside and p-nitrophenyl 2-acetamide-2-deoxy-beta-D-galactopyranoside are 0.43 mM, 30.1 micronmol of p-nitrophenol/min per mg and 0.19 mM, 8.6 micronmol of p-nitrophenol/min per mg respectively. 7. It is inhibited by Hg2+, Fe3+, acetate, some lactones, N-acetylgalactosamine, N-acetylglucosamine and mannose. 8. Mixed-substrates analysis and Ki values for competitive inhibitors indicated that beta-N-acetylglucosaminidase and beta-N-acetylgalactosaminidase activities are catalysed by the enzyme at the same active site.

Effect of leukocyte hydrolases on bacteria. X. The role played by leukocyte factors, cationic polyelectrolytes, and by membrane-damaging agents in the lysis of Staphylococcus aureus: relation to chronic inflammatory processes

A heat-stable factor present in extracts of human blood leukocytes is capable of lysing young Staphylococcus aureus at pH 5.0. Lysis is characterized by breakdown of cell-wall components as judged by electron microscopic and biochemical analysis. The leukocyte extracts can be replaced by a variety of agents known to injure cell membranes, e.g., leukocyte cationic protein histone, polymyxin B, colimycin, phospholipase A, and lysolecithin. The mechanisms by which all these agents bring about the degradation of the staphylococcal walls was studied. By using 14C-labeled cell walls devoid of cytoplasmic structures, it was demonstrated that none of the above-mentioned agents had a direct lytic effect on purified cell walls. On the other hand, when any of these agents first interacted with intact staphylococci, a factor (presumably an autolysin) was generated that directly lysed the cell walls. Lysis of cell walls in the presence of intact staphylococci used as a source of autolysin was strongly inhibited by a variety of anionic polyelectrolytes such as heparine and liquoid. The possible role played by bacterial autolysins in the generation of microbial cell-wall components capable of triggering chronic inflammation is discussed.

The immunochemistry of peptidoglycan. Antibodies against a synthetic immunogen cross-reacting with an interpeptide bridge of peptidoglycan

An albumin-peptide conjugate was synthesized, which carries pentaglycine peptides with C-terminal glycine residues as found in the interpeptide bridges of the peptidoglycan of many staphylococci. Immunization of rabbits with this synthetic immunogen yielded antisera containing predominantly antibodies against the peptide moiety of the conjugate. The quantitative precipitin and the Ouchterlony agar gel reaction with several synthetic protein-peptide-conjugates, immunoaffinity chromatography of the antisera on Sepharose-(Gly-Gly-Gly-Gly-Gly)n and hapten inhibition studies with several synthetic peptides and peptide derivatives demonstrated that the antibodies were highly specific for oligoglycine peptides with C-terminal glycine. These antibodies also reacted strongly with staphylococcal peptidoglycans with an interpeptide bridge composed of pentaglycine peptides or of pentaglycine peptides in which part of the glycine residues were replaced by L-serine. In contrast, all the peptidoglycans lacking interpeptide bridges composed of glycine residues gave no precipitin reaction at all. The final proof for identical determinant groups of albumin-(CH2CO-Gly-Gly-Gly-Gly-Gly)31 and the staphylococcal peptidoglycans applied in the precipitin reaction was furnished by double gel diffusion studies and by hapten inhibition of the precipitin reaction between antisera to albumin-(CH2CO-Gly-Gly-Gly-Gly-Gly)31 and the corresponding peptidoglycans. For rapid screening of the different peptidoglycans, a latex agglutination test was elaborated. Purified antibodies were adsorbed to latex particles, and the titers with the particular peptidoglycans were then determined. The test was highly sensitive, in that 10 nanograms of peptidoglycan could still be detected.

Bacteriolytic activity in staphylococci

The bacteriolytic activity of Staphylococcus aureus and Staphylococcus albus strains was tested with various media. Whereas S. aureus strains were found to be active under all conditions, the percentage of active S. albus strains was significantly influenced by the composition of the medium. Ionic strength and concentration of the organic nitrogen source were found to be the main factors affecting the expression of bacteriolytic activity of straphylococci. Virtually all of 318 S. aureus and 603 S. albus strains were active on a medium containing 3% peptone, 0.3% glucose, 0.2% yeast extract, 0.1% disodium phosphate, 2.2% sodium chloride and 0.9% agar. The optimal conditions for the bacteriolytic activity of S. aureus strains were different from those of most S. albus strains. Within S. albus, optimal conditions differed also from strain to strain. It is suggested that further studies on this subject may prove useful for the identification and taxonomy of staphylococci. A possible relationship between the production of extracellular bacteriolytic enzymes and pathogenic properties of staphylococci is also considered.

The purification and properties of extracellular glycosidases of the cellular slime mould Dictyostelium discoideum

The purification of beta-N-acetylhexosaminidase, alpha-glucosidase, alpha-mannosidase and beta-glucosidase from the spent growth medium of Dictyostelium discoideum strain Ax-2 myxamoebae is described. beta-N-Acetylhexosaminidase and alpha-glucosidase were obtained in high yield and as homogeneous preparations whereas the alpha-mannosidase preparation consisted of two electrophoretically distinct isoenzymes. The physical, chemical and kinetic properties of these enzymes are described.

Control of the production of exo-beta-N-acetylglucosaminidase by Bacillus subtilis B

1. The control of exo-beta-N-acetylglucosaminidase (EC 3.2.1.30) production by Bacillus subtilis B growing on a chemically defined medium was studied. 2. The enzyme was repressed during exponential growth by those carbon sources that enter the glycolytic pathway above the level of phosphoenolpyruvate. When exponential growth ceased as a result of low concentrations of the nitrogen, carbon or metal ion components of the medium, the enzyme was formed and its amount could be increased by the addition of cell-wall fragments as inducer. 3. The enzyme was de-repressed and could be induced during exponential growth on non-glycolytic compounds metabolized directly into pyruvate, acetyl-CoA or tricarboxylic acid cycle intermediates. 4. The major difference in the metabolism of the organism utilizing these two groups of compound was the existence of high activities of phosphoenolpyruvate carboxylase required for gluconeogenesis. 5. It is concluded that the de-repression of glucosaminidase occurs when the only principal change detected in the intermediary metabolism of the organism was the presence of high activities of phosphoenolpyruvate carboxylase. 6. When the organism was grown on media containing repressing compounds, the enzyme was only de-repressed on entry of the cells into the initial stages of sporulation, where phosphoenolpyruvate carboxylase activity, even in the presence of excess of glucose, increased in parallel with glucosaminidase, neutral proteinase and alkaline phosphatase activities. 7. These results suggest a strong link, at the level of the tricarboxylic acid cycle, between the control of phosphoenolpyruvate carboxylase and the control of the de-repression of glucosaminidase and sporulation.

Partial purification and properties of a beta-N-acetylglucosaminidase from the fungus Sclerotinia fructigena

1. As cultures of the fungus Sclerotinia fructigena autolysed, the filtrates contained increasing quantities of a beta-N-acetylglucosaminidase. 2. The enzyme was purified up to 42-fold by a combination of isoelectric focusing and gel filtration. 3. It ran as a single band in cellulose acetate strip electrophoresis and in isoelectric focusing (pI3.76). 4. The enzyme did not readily hydrolyse chitin or a glycopeptide with terminal N-acetylglucosamine residues, but rapidly degraded the N-acetylglucosamine dimer NN'-diacetylchitobiose; the monomer was readily utilized by the fungus as a nitrogen source. The K(m) value for hydrolysis of p-nitrophenyl beta-2-acetamido-2-deoxy-d-glucopyranoside at 37 degrees C was 2.0mm. The Sclerotinia enzyme was generally less susceptible to inhibition by 2-acetamido-2-deoxygluconolactone and other related sugars than the corresponding enzyme from other sources. Inhibition by excess of substrate was observed. 5. The culture filtrate also contained N-acetylgalactosaminidase activity; conflicting evidence was obtained as to whether the same enzyme was responsible for both hexosaminidase activities.

Bacteriolytic enzymes from Staphylococcus aureus. Purification of an endo-beta-N-acetylglucosaminidase

On cultivation of Staphylococcus aureus in a complex liquid medium, bacteriolytic activity is found extracellularly. The maximal amount was found at the end of the exponential growth phase in batch culture, but in continuous culture run under similar conditions the yield was doubled. Isoelectric focusing of dialysed crude culture supernatants showed that the bacteriolytic activity of all four strains studied (M18, 524, Wood 46 and Duncan) was heterogeneous. The most alkaline peak of activity (isoelectric point 9.5+/-0.1) was assayed against Micrococcus lysodeikticus turbidimetrically. This bacteriolytic activity was purified more than 70-fold after continuous dialysis by adsorption on CM-Sephadex, precipitation with ethanol, heat purification, isoelectric focusing and Sephadex G-100 chromatography. The purified enzyme (isoelectric point 9.6+/-0.1) was found to give a single band on polyacrylamide-gel and cellulose acetate electrophoresis and was devoid of all 14 staphylococcal enzymes and toxins assayed for. The molecular weight is 70000+/-5000 as estimated by Sephadex G-100 and G-200 chromatography. The marked instability of the partially and highly purified enzyme was investigated. The mode of action and some properties of this enzyme are given in the following papers (Wadström & Hisatsune, 1970; Wadström, 1970). These results indicate that this extracellular enzyme which is produced by several strains of S. aureus is not a ;lysozyme' (endo-beta-N-acetylmuramidase) as previously suggested, but an endo-beta-N-acetylglucosaminidase.

Bacteriolytic enzymes from Staphylococcus aureus. Properties of the endo-beta-N-acetylglucosaminidase

An extracellular bacteriolytic endo-beta-N-acetylglucosaminidase has been purified and its specificity of action has been investigated (Wadström & Hisatsune, 1970a,b). Some enzymic properties, such as optimum pH for enzyme activity on whole cells and cell walls of Micrococcus lysodeikticus and Staphylococcus aureus and optimum pH for stability, have been studied. The activity was maximum in 0.05m-tris-hydrochloric acid buffer, pH7.0. A higher ionic strength inhibited cell-wall hydrolysis. Since the crude and purified enzymes were found to be unstable on storage, the stabilizing and inhibiting effects of several compounds were investigated. Several heavy metal ions inactivated the enzyme at very low concentrations. Thiol compounds stabilized and thiol-reacting compounds partly inhibited the activity. Crude and purified glucosaminidase was found to be heat-stable at acidic pH and unstable at alkaline pH as previously found for several lysozymes (endo-beta-N-acetylmuramidases). Other properties of the staphylococcal enzyme and hen's-egg-white lysozyme have been compared, since the modes of action of the two are quite similar (Wadström & Hisatsune, 1970b).