Influence of cultivation conditions on production of lignocellulolytic enzymes by Ceriporiopsis subvermispora

The aim of this work was to make a survey describing factors that influence the production of extracellular enzymes by white-rot fungus Ceriporiopsis subvermispora responsible for the degradation of lignocellulolytic materials. These factors were: carbon sources (glucose, cellulose, hemicellulose, lignin, maltose and starch), nitrogen sources (ammonium sulphate, potassium nitrate, urea, albumin and peptone), pH, temperature and addition of three different concentrations of Cu²⁺ and Mn²⁺. The cellulase and xylanase activities were similar in medium with different carbon sources and the highest cellulase and xylanase activities were measured in medium with urea and potassium nitrate as nitrogen sources, respectively. The highest laccase activity was observed in medium with lignin and peptone as carbon and nitrogen sources. In other experiments, time course of production of lignocellulolytic enzymes by white-rot fungus C. subvermispora in medium with lignin or glucose as carbon sources was observed.     

Characterization and use of a bacterial lignin peroxidase with an improved manganese-oxidative activity

Peroxidases are well-known biocatalysts produced by all organisms, especially microorganisms, and used in a number of biotechnological applications. The enzyme DypB from the lignin-degrading bacterium Rhodococcus jostii was recently shown to degrade solvent-obtained fractions of a Kraft lignin. In order to promote the practical use, the N246A variant of DypB, named Rh_DypB, was overexpressed in E. coli using a designed synthetic gene: by employing optimized conditions, the enzyme was fully produced as folded holoenzyme, thus avoiding the need for a further time-consuming and expensive reconstitution step. By a single chromatographic purification step, > 100 mg enzyme/L fermentation broth with a > 90% purity was produced. Rh_DypB shows a classical peroxidase activity which is significantly increased by adding Mn²⁺ ions: kinetic parameters for H₂O₂, Mn²⁺, ABTS, and 2,6-DMP were determined. The recombinant enzyme shows a good thermostability (melting temperature of 63–65 °C), is stable at pH 6–7, and maintains a large part of the starting activity following incubation for 24 h at 25–37 °C. Rh_DypB activity is not affected by 1 M NaCl, 10% DMSO, and 5% Tween-80, i.e., compounds used for dye decolorization or lignin-solubilization processes. The enzyme shows broad dye-decolorization activity, especially in the presence of Mn²⁺, oxidizes various aromatic monomers from lignin, and cleaves the guaiacylglycerol-β-guaiacyl ether (GGE), i.e., the Cα-Cβ bond of the dimeric lignin model molecule of β-O-4 linkages. Under optimized conditions, 2 mM GGE was fully cleaved by recombinant Rh_DypB, generating guaiacol in only 10 min, at a rate of 12.5 μmol/min mg enzyme.

     

Peroxidation of linoleic acid during the oxidation of phenols by fungal laccase

A system comprising laccase and a suitable phenol such as 4-hydroxybenzoic acid (HBA) or synthetic lignin (DHP) exhaustively peroxidized linoleic acid in acetate buffer. The presence of phenols in lignin was essential since an exhaustively methylated preparation of the same lignin did not support peroxidation. The peroxidation rate was greatly enhanced by Mn²⁺, which was oxidized to Mn³⁺ by laccase/HBA, whereas H₂O₂ inhibited strongly due to rapid reduction of Mn³⁺ by H₂O₂ with concomitant formation of O₂. When acetate was replaced by Mn³⁺–chelating oxalate or malonate, there was no change in peroxidation rates in the absence of Mn²⁺, whereas strong inhibition was observed in the presence of Mn²⁺. In case of malonate part of the inhibition was due to H₂O₂ formation as a result of Mn³⁺ reduction by malonate. These findings suggest that laccase may contribute to fungal lipid peroxidation in vivo thus expanding its role in the biodegradation of lignin and other recalcitrant aromatic compounds.     

Depolymerization of low-rank coal by extracellular fungal enzyme systems. II. The ligninolytic enzymes of the coal-humic-acid-depolymerizing fungus Nematoloma frowardii b19

The production of ligninolytic enzymes was studied in surface cultures of the South American white-rot fungus Nematoloma frowardii b19 and four other strains of this ecophysiological group (Clitocybula dusenii b11, Auricularia sp. m37a, wood isolates u39 and u45), which are able to depolymerize low-rank-coal-derived humic acids with the formation of fulvic-acid-like compounds. The fungi produced the three crucial enzymes of lignin degradation – lignin peroxidase, manganese peroxidase and laccase. In the case of N. frowardii b19, laccase and the two peroxidases could be stimulated by veratryl alcohol. Manganese (II) ions (Mn²⁺) caused a rapid increase of Mn peroxidase activity accompanied by the complete repression of lignin peroxidase. Under nitrogen-limited conditions the growth as well as the production of ligninolytic enzymes was partly repressed. During the depolymerization process of coal humic acids using solid agar media, gradients of ligninolytic enzyme activities toward 2,2′-azinobis(3-ethylbenzthiazoline-6-sulphonate) and syringaldazine were detectable inside the agar medium. Received: 5 August 1996 / Received revision: 13 November 1996 / Accepted: 15 November 1996     

Identification of DypB from Rhodococcus jostii RHA1 as a lignin peroxidase

Rhodococcus jostii RHA1, a polychlorinated biphenyl-degrading soil bacterium whose genome has been sequenced, shows lignin degrading activity in two recently developed spectrophotometric assays. Bioinformatic analysis reveals two unannotated peroxidase genes present in the genome of R. jostii RHA1 with sequence similarity to open reading frames in other lignin-degrading microbes. They are members of the Dyp peroxidase family and were annotated as DypA and DypB, on the basis of bioinformatic analysis. Assay of gene deletion mutants using a colorimetric lignin degradation assay reveals that a ΔdypB mutant shows greatly reduced lignin degradation activity, consistent with a role in lignin breakdown. Recombinant DypB protein shows activity in the colorimetric assay and shows Michaelis-Menten kinetic behavior using Kraft lignin as a substrate. DypB is activated by Mn(2+) by 5-23-fold using a range of assay substrates, and breakdown of wheat straw lignocellulose by recombinant DypB is observed over 24-48 h in the presence of 1 mM MnCl(2). Incubation of recombinant DypB with a β-aryl ether lignin model compound shows time-dependent turnover, giving vanillin as a product, indicating that C(α)-C(β) bond cleavage has taken place. This reaction is inhibited by addition of diaphorase, consistent with a radical mechanism for C-C bond cleavage. Stopped-flow kinetic analysis of the DypB-catalyzed reaction shows reaction between the intermediate compound I (397 nm) and either Mn(II) (k(obs) = 2.35 s(-1)) or the β-aryl ether (k(obs) = 3.10 s(-1)), in the latter case also showing a transient at 417 nm, consistent with a compound II intermediate. These results indicate that DypB has a significant role in lignin degradation in R. jostii RHA1, is able to oxidize both polymeric lignin and a lignin model compound, and appears to have both Mn(II) and lignin oxidation sites. This is the first detailed characterization of a recombinant bacterial lignin peroxidase.     

Purification and biochemical characterization of two extracellular peroxidases from Phanerochaete chrysosporium responsible for lignin biodegradation

Two extracellular peroxidases from Phanerochaete chrysosporium, namely a lignin peroxidase (LiP) and manganese peroxidase (MnP), were purified simultaneously by applying successively, ultrafiltration, ion-exchange and gel filtration chromatography. LiP and MnP have a molecular mass of 36 and 45 kDa, respectively. The optimal pHs for LiP and MnP activities were 3.0 and 4.5, respectively. Both peroxidases showed maximal activity at 30 °C and moderate thermostability. MnP activity was strongly inhibited by Fe²⁺, Zn²⁺, Mg²⁺ and Hg²⁺, and enhanced by Mn²⁺, Ca²⁺ and Cu²⁺. LiP activity was enhanced by Ca²⁺, Na⁺ and Co²⁺ and it was inhibited in the presence of K⁺, Hg⁺, Fe²⁺, Mg²⁺ and high concentrations of Cu²⁺ and Zn²⁺. The K_m and V_max for LiP toward veratryl alcohol as a substrate were 0.10 mM and 15.2 U mg⁻¹, respectively and for MnP toward Mn²⁺, they were respectively 0.03 mM and 25.5 U mg⁻¹. The two peroxidases were also able to break down rice lignin in a small-scale solid state treatment system. Data suggest these two peroxidases may be considered as potential candidates for the development of enzyme-based technologies for lignin degradation.     

The ligninolytic activities of Lentinus edodes and Phanerochaete chrysosporium

Summary Two important lignin-degrading fungi with existing or potential applications in the production of food, feed and/or fiber products from wood are Lentinus edodes (Berk.; Sing.=Lentinula edodes [Pegler]) and Phanerochaete chrysosporium (Burds). This study discusses their relative ability to degrade lignin and the factors controlling their ligninolytic activity (synthetic ¹⁴C-lignin¹⁴CO₂). Ligninolytic activity in P. chrysosporium is known to develop after the fungus ceases vegetative growth, and to require both O₂ and an exogenous carbon source such as glucose. It has an extracellular ligninase in high titer which is assayed by the oxidation of veratryl alcohol to veratraldehyde. Here, P. chrysosporium was found to have a high capacity for lignin degradation (it was not easily saturated with lignin). Certain inorganic elements, including Fe²⁺, Ca²⁺ and Mo⁶⁺, were found to stimulate its ligninolytic activity. Calcium addition was required, with 40 ppm Ca²⁺ giving the highest activity. As in P. chrysosporium, ligninolytic activity in L. edodes was found to require both O₂ and an exogenous carbon source. However, in contrast to P. chrysosporium, L. edodes was only moderately ligninolytic, had a lower capacity for lignin degradation (was more easily saturated with lignin), and showed maximal activity only during the vegetative growth period. Also in contrast to P. chrysosporium, ligninolytic activity in L. edodes was not stimulated by Ca²⁺. Instead, manganese was required, with 10 ppm Mn²⁺ giving optimal activity. An extracellular ligninase capable of oxidizing veratryl alcohol to veratraldehyde was not detected in L. edodes.     

Lignocellulosic polysaccharides and lignin degradation by wood decay fungi: the relevance of nonenzymatic Fenton-based reactions

The brown rot fungus Wolfiporia cocos and the selective white rot fungus Perenniporia medulla-panis produce peptides and phenolate-derivative compounds as low molecular weight Fe³⁺-reductants. Phenolates were the major compounds with Fe³⁺-reducing activity in both fungi and displayed Fe³⁺-reducing activity at pH 2.0 and 4.5 in the absence and presence of oxalic acid. The chemical structures of these compounds were identified. Together with Fe³⁺ and H₂O₂ (mediated Fenton reaction) they produced oxygen radicals that oxidized lignocellulosic polysaccharides and lignin extensively in vitro under conditions similar to those found in vivo. These results indicate that, in addition to the extensively studied Gloeophyllum trabeum—a model brown rot fungus—other brown rot fungi as well as selective white rot fungi, possess the means to promote Fenton chemistry to degrade cellulose and hemicellulose, and to modify lignin. Moreover, new information is provided, particularly regarding how lignin is attacked, and either repolymerized or solubilized depending on the type of fungal attack, and suggests a new pathway for selective white rot degradation of wood. The importance of Fenton reactions mediated by phenolates operating separately or synergistically with carbohydrate-degrading enzymes in brown rot fungi, and lignin-modifying enzymes in white rot fungi is discussed. This research improves our understanding of natural processes in carbon cycling in the environment, which may enable the exploration of novel methods for bioconversion of lignocellulose in the production of biofuels or polymers, in addition to the development of new and better ways to protect wood from degradation by microorganisms.     

The modifying effect of manganese on the enzymic profiles and pathways of carbohydrate metabolism in rat liver and adipose tissue during development

The effect of Mn²⁺ on the pattern of emergence of enzymes in rat liver and adipose tissue was studied in weaned rats given a milk diet (high fat) or sucrose-casein diet (high carbohydrate) for three weeks. Addition of Mn²⁺ to the high fat diet was associated with induction of key glycolytic, lipogenic and pentose pathway enzymes in both liver and adipose tissue; parallel increases were found in the incorporation of [1-¹⁴C] glucose into lipid and CO₂. Mn²⁺ induced a change in the profile of enzyme activity similar in pattern to that found in rats given a high sucrose diet or that produced by insulin treatment. Mn²⁺ appears partially to overcome the regulatory feed-back mechanisms of the high fat diet and to provide a signal for the coordinated increase of glucose catabolic and lipogenic processes.     

Combined effects of ethanol and manganese on cultured neurons and glia

Manganese is essential for normal development and activity of the nervous tissue. Mn²⁺ ions are involved in protein synthesis and may prevent free radical damage. Since it is now established that alcohol degradation may produce free radicals, we studied the effect of Mn²⁺ on ethanol induced alterations using cultured nerve cells as an experimental model of the central nervous system. Neurons and glial cells were cultured from rat brain cortex; a tumoral rat glial cell line (C6) was also examined. We measured enzymatic markers of nerve cell maturation (enolase, glutamine synthetase) and superoxide dismutase, a scavenger of free radicals; all these enzymes being activated by Mn²⁺ ions. Only for the glial cell types an alcohol antagonizing effect was found when Mn²⁺ was combined with ethanol. Neurons were not sensitive to that Mn²⁺ effect.     

Involvement of ligninolytic enzymes and Fenton-like reaction in humic acid degradation by Trametes sp

Trametes sp. M23, isolated from biosolids compost was found to decompose humic acids (HA). A low N (LN) medium (C/N, 53) provided suitable conditions for HA degradation, whereas in a high N (HN) medium (C/N, 10), HA was not degraded. In the absence of Mn²⁺, HA degradation was similar to that in Mn²⁺-containing medium. In contrast, MnP activity was significantly affected by Mn²⁺. Laccase activity exhibited a negative correlation to HA degradation, while LiP activity was not detected. Thus, ligninolytic enzymes activity could provide only a partial explanation for the HA-degradation mechanism. The decolorization of two dyes, Orange II and Brilliant Blue R250, was also determined. Similar to HA degradation, under LN conditions, decolorization occurred independently of the presence of Mn²⁺. We investigated the possible involvement of a Fenton-like reaction in HA degradation. The addition of DMSO, an OH-radical scavenger, to LN media resulted in a significant decrease in HA bleaching. The rate of extracellular Fe³⁺ reduction was much higher in the LN vs. HN medium. In addition, the rate of reduction was even higher in the presence of HA in the medium. In vitro HA bleaching in non-inoculated media was observed with H₂O₂ amendment to a final concentration of 200 mM (obtained by 50 mM amendments for 4 days) and Fe²⁺ (36 mM). After 4 days of incubation, HA decolorization was similar to the biological treatment. These results support our hypothesis that a Fenton-like reaction is involved in HA degradation by Trametes sp. M23.     

Trypanosoma cruzi phospho enol pyruvate carboxykinase (ATP-dependent) : transition metal ion requirement for activity and sulfhydryl group reactivity

We studied the transition metal ion requirements for activity and sulfhydryl group reactivity in phosphoenolpyruvate carboxykinase (PEP-carboxykinase; ATP:oxaloacetate carboxylase (transphosphorylating), EC 4.1.1.49), a key enzyme in the energy metabolism of the protozoan parasite Trypanosoma (Schizotrypanum) cruzi. As for other PEP-carboxykinases this enzyme has a strict requirement of transition metal ions for activity, even in the presence of excess Mg²⁺ ions for the carboxylation reaction; the order of effectiveness of these ions as enzyme activators was: Co²⁺ > Mn²⁺ > Cd^u2+ > Ni²⁺ ⪢ Fe²⁺ > VO²⁺, while Zn²⁺ and Ca²⁺ had no activating effects. When we investigated the effect of varying the type or concentration of the transition metal ions on the kinetic parameters of the enzyme the results suggested that the stimulatory effects of the transition metal center were mostly associated with the activation of the relatively inert CO₂ substrate. The inhibitory effects of 3-mercaptopicolinic acid (3MP) on the enzyme were found to depend on the transition metal ion activator: for the Mn²⁺ activated enzyme the inhibition was purely non-competitive (K_ii = K_is) towards all substrates, while for the Co²⁺-activated enzyme the inhibitor was much less effective, produced a mixed-type inhibition and affected differentially the interaction of the enzyme with its substrates. The modification of a single, highly reactive, cysteine per enzyme molecule by 5,5′-dithiobis(2-nitro-benzoate) (DTNB) lead to an almost complete inhibition of Mn²⁺-activated T. cruzi PEP-carboxykinase; however, in contrast with the results of previous studies in vertebrate and yeast enzymes, the substrate ADP slowed the chemical modification and enzyme inactivation but did not prevent it. PEP and HCO₃⁻ had no significant effect on the rate or extent of the enzyme inactivation. The kinetics of the enzyme inactivation by DTNB was also dependent on the transition metal activator, being much slower for the Co²⁺-activated enzyme than for its Mn²⁺-activated counterpart. When the bulkier but more hydrophobic reagent N-(7-dimethylamino-4-methylcoumarinyl)maleimide (DACM) was used the enzyme was slowly and incompletely inactivated in the presence of Mn²⁺ and ADP afforded almost complete protection from inactivation; in the presence of Co²⁺ the enzyme was completely resistant to inactivation. Taken together, our results indicate that the parasite enzyme has a specific requirement of transition metal ions for activity and that they modulate the reactivity of a single, essential thiol group, different from the hyperreactive cysteines present in vertebrate or yeast enzymes.     

Genomics and biochemistry investigation on the metabolic pathway of milled wood and alkali lignin-derived aromatic metabolites of <Emphasis Type="Italic">Comamonas serinivorans</Emphasis> SP-35

Background

The efficient depolymerization and utilization of lignin are one of the most important goals for the renewable use of lignocelluloses. The degradation and complete mineralization of lignin by bacteria represent a key step for carbon recycling in land ecosystems as well. However, many aspects of this process remain unclear, for example, the complex network of metabolic pathways involved in the degradation of lignin and the catabolic pathway of intermediate aromatic metabolites. To address these subjects, we characterized the deconstruction and mineralization of lignin with milled wood lignin (MWL, the most representative molecule of lignin in its native state) and alkali lignin (AL), and elucidated metabolic pathways of their intermediate metabolites by a bacterium named Comamonas serinivorans SP-35.

Results

The degradation rate of MWL reached 30.9%, and its particle size range was decreased from 6 to 30 µm to 2–4 µm—when cultured with C. serinivorans SP35 over 7 days. FTIR analysis showed that the C–C and C–O–C bonds between the phenyl propane structures of lignin were oxidized and cleaved and the side chain structure was modified. More than twenty intermediate aromatic metabolites were identified in the MWL and AL cultures based on GC–MS analysis. Through genome sequencing and annotation, and from GC–MS analysis, 93 genes encoding 33 enzymes and 5 regulatory factors that may be involved in lignin degradation were identified and more than nine metabolic pathways of lignin and its intermediates were predicted. Of particular note is that the metabolic pathway to form the powerful antioxidant 3,4-dihydroxyphenylglycol is described for the first time in bacteria.

Conclusion

Elucidation of the β-aryl ether cleavage pathway in the strain SP-35 indicates that the β-aryl ether catabolic system is not only present in the family of Sphingomonadaceae, but also other species of bacteria kingdom. These newly elucidated catabolic pathways of lignin in strain SP-35 and the enzymes responsible for them provide exciting biotechnological opportunities for lignin valorization in future.

     

Biodepolymerization studies of low rank Indian coals

Biodepolymerization of some of the lower rank Indian coals by Pleurotus djamor, Pleurotus citrinopileatus and Aspergillus species were studied in a batch system. The main disadvantage in burning low rank coals is the low calorific values. To get the maximum benefit from the low rank coals, the non fuel uses of coals needs to be explored. The liquefaction of coals is the preliminary processes for such approaches. The present study is undertaken specifically to investigate the optimization of bio depolymerization of neyveli lignite by P. djmor. The pH of the media reached a constant value of about 7.8 by microbial action. The effect of different carbon and nitrogen sources and influence of chelators and metal ions on depolymerization of lignite were also studied. Lignite was solubilized by P. djamor only to a limited extent without the addition of carbon and nitrogen sources. Sucrose was the best suitable carbon source for coal depolymerization by P. djamor and sodium nitrated followed by urea was the best nitrogen source. The Chelators like salicylic acid, TEA and metal ions Mg²⁺, Fe³⁺, Ca²⁺, Cu²⁺, Mn²⁺ has enhanced the lignite solubilization process. The finding of the study showed that, compared to sub-bituminous and bituminous coal, the lignite has higher rate of solubilization activity.     

Characteristics of extracellular proteases produced by Bacillus laterosporus and Flavobacterium sp. isolated from gelatinfactory effluents

Forty bacterial isolates from the effluents of a gelatin factory (Jabalpur, India) were screened for protease activity and the two most potent producers were identified as Bacillus laterosporus and a Flavobacterium sp. The enzymes of both isolates were optimal at pH 8 and 60°C, with maximum activity after 90 min. The enzyme activity of B. laterosporus was suppressed by Fe²⁺, Mg²⁺, Mn²⁺ and Zn²⁺ ions but was enhanced by Ba²⁺ and Ca²⁺. That of Flavobacterium sp. was suppressed by Mg²⁺ and Mn²⁺ ions but enhanced by Ba²⁺, Ca²⁺ and Fe²⁺. The enzyme activity of the former was strongly inhibited by KCN, whereas that of the latter was only slightly inhibited by 8-hydroxyquinoline.     

Manganese‐oxidizing bacteria mediate the degradation of 17α‐ethinylestradiol

Manganese (II) and manganese‐oxidizing bacteria were used as an efficient biological system for the degradation of the xenoestrogen 17α‐ethinylestradiol (EE2) at trace concentrations. Mn²⁺‐derived higher oxidation states of Mn (Mn³⁺, Mn⁴⁺) by Mn²⁺‐oxidizing bacteria mediate the oxidative cleavage of the polycyclic target compound EE2. The presence of manganese (II) was found to be essential for the degradation of EE2 by Leptothrix discophora, Pseudomonas putida MB1, P. putida MB6 and P. putida MB29. Mn²⁺‐dependent degradation of EE2 was found to be a slow process, which requires multi‐fold excess of Mn²⁺ and occurs in the late stationary phase of growth, implying a chemical process taking place. EE2‐derived degradation products were shown to no longer exhibit undesirable estrogenic activity.     

Altered microbial community structure and organic matter composition under elevated CO2 and N fertilization in the duke forest

The dynamics and fate of terrestrial organic matter (OM) under elevated atmospheric CO₂ and nitrogen (N) fertilization are important aspects of long‐term carbon sequestration. Despite numerous studies, questions still remain as to whether the chemical composition of OM may alter with these environmental changes. In this study, we employed molecular‐level methods to investigate the composition and degradation of various OM components in the forest floor (O horizon) and mineral soil (0–15 cm) from the Duke forest free air CO₂ enrichment (FACE) experiment. We measured microbial responses to elevated CO₂ and N fertilization in the mineral soil using phospholipid fatty acid (PLFA) profiles. Increased fresh carbon inputs into the forest floor under elevated CO₂ were observed at the molecular‐level by two degradation parameters of plant‐derived steroids and cutin‐derived compounds. The ratios of fungal to bacterial PLFAs and Gram‐negative to Gram‐positive bacterial PLFAs decreased in the mineral soil with N fertilization, indicating an altered soil microbial community composition. Moreover, the acid to aldehyde ratios of lignin‐derived phenols increased with N fertilization, suggesting enhanced lignin degradation in the mineral soil. ¹H nuclear magnetic resonance (NMR) spectra of soil humic substances revealed an enrichment of leaf‐derived alkyl structures with both elevated CO₂ and N fertilization. We suggest that microbial decomposition of SOM constituents such as lignin and hydrolysable lipids was promoted under both elevated CO₂ and N fertilization, which led to the enrichment of plant‐derived recalcitrant structures (such as alkyl carbon) in the soil.     

On the Divalent Metal Ion Dependence of DNA Cleavage by Restriction Endonucleases of the EcoRI Family

Restriction endonucleases of the PD…D/EXK family need Mg²⁺ for DNA cleavage. Whereas Mg²⁺ (or Mn²⁺) promotes catalysis, Ca²⁺ (without Mg²⁺) only supports DNA binding. The role of Mg²⁺ in DNA cleavage by restriction endonucleases has elicited many hypotheses, differing mainly in the number of Mg²⁺ involved in catalysis. To address this problem, we measured the Mg²⁺ and Mn²⁺ concentration dependence of DNA cleavage by BamHI, BglII, Cfr10I, EcoRI, EcoRII (catalytic domain), MboI, NgoMIV, PspGI, and SsoII, which were reported in co-crystal structure analyses to bind one (BglII and EcoRI) or two (BamHI and NgoMIV) Me²⁺ per active site. DNA cleavage experiments were carried out at various Mg²⁺ and Mn²⁺ concentrations at constant ionic strength. All enzymes show a qualitatively similar Mg²⁺ and Mn²⁺ concentration dependence. In general, the Mg²⁺ concentration optimum (between ∼ 1 and 10 mM) is higher than the Mn²⁺ concentration optimum (between ∼ 0.1 and 1 mM). At still higher Mg²⁺ or Mn²⁺ concentrations, the activities of all enzymes tested are reduced but can be reactivated by Ca²⁺. Based on these results, we propose that one Mg²⁺ or Mn²⁺ is critical for restriction enzyme activation, and binding of a second Me²⁺ plays a role in modulating the activity. Steady-state kinetics carried out with EcoRI and BamHI suggest that binding of a second Mg²⁺ or Mn²⁺ mainly leads to an increase in K_m, such that the inhibitory effect of excess Mg²⁺ or Mn²⁺ can be overcome by increasing the substrate concentration. Our conclusions are supported by molecular dynamics simulations and are consistent with the structural observations of both one and two Me²⁺ binding to these enzymes.     

In vivo biosynthesis of peptidophosphogalactomannan in Penicillium charlesii

Aspergillus nidulans was grown on media with added amounts of manganese ranging from 0–2.5 μM. Manganese deficiency prevented cleistothecium development, although good vegetative growth was retained. Subsequent analysis of the mycelium produced under Mn²⁺ deficient growth revealed that α-1,3 glucan, the main carbon and energy source for fructification, was virtually absent from the cell wall. Several enzymes related to cell wall composition were investigated. β-1,3 glucanase, and very remarkably, α-1,3 glucanase reached about the same activity on the Mn²⁺ deficient and sufficient media, but amylase and protease were about 60 and 75% lower respectively on the Mn²⁺ deficient media and the correlation of these findings is discussed.