Advances in phytase research

Since its discovery in 1907, a complex of technological developments has created a potential $500 million market for phytase as an animal feed additive. During the last 30 years, research has led to increased use of soybean meal and other plant material as protein sources in animal feed. One problem that had to be overcome was the presence of antinutritional factors, including phytate, in plant meal. Phytate phosphorus is not digested by monogastric animals (e.g., hogs and poultry), and in order to supply enough of this nutrient, additional phosphate was required in the feed ration. Rock phosphate soon proved to be a cost-effective means of supplying this additional phosphorus, and the excess phytin phosphorus could be disposed of easily with the animals' manure. However, this additional phosphorus creates a massive environmental problem when the land's ability to bind it is exceeded. Over the last decade, numerous feed studies have established the efficacy of a fungal phytase, A. niger NRRL 3135, to hydrolyze phytin phosphorus in an animal's digestive tract, which benefits the animal while reducing total phosphorus levels in manure. The gene for phytase has now been cloned and overexpressed to provide a commercial source of phytase. This monomeric enzyme, a type of histidine acid phophatase (HAP), has been characterized and extensively studied. HAPs are also found in other fungi, plants, and animals. Several microbial and plant HAPs are known to have significant phytase activity. A second A. niger phytase (phyB), a tetramer, is known and, like phyA, has had its X-ray crystal structure determined. The model provided by this crystal structure research has provided an enhanced understanding of how these molecules function. In addition to the HAP phytase, several other phytases that lack the unique HAP active site motif RHGXRXP have been studied. The best known group of the non-HAPs is phytase C (phyC) from the genus Bacillus. While a preliminary X-ray crystallographic analysis has been initiated, no enzymatic mechanism has been proposed. Perhaps the pivotal event in the last century that created the need for phytase was the development of modern fertilizers after the Second World War. This fostered a transformation in agriculture and a tremendous increase in feed-grain production. These large quantities of cereals and meal in turn led to the transition of one segment of agriculture into "animal agriculture," with their its animal production capability. The huge volumes of manure spawned by these production units in time exceeded both the capacity of their crops and crop lands to utilize or bind the increased amount of phosphorus. Nutrient runoff from this land has now been linked to a number of blooms of toxin-producing microbes. Fish kills associated with these blooms have attracted public and governmental concern, as well as greater interest in phytase as a means to reduce this phosphorus pollution. Phytase research efforts now are focused on the engineering of an improved enzyme. Improved heat tolerance to allow the enzyme to survive the brief period of elevated temperature during the pelletization process is seen as an essential step to lower its cost in animal feed. Information from the X-ray crystal structure of phytase is also relevant to improving the pH optimum, substrate specificity, and enzyme stability. Several studies on new strategies that involve synergistic interactions between phytase and other hydrolytic enzymes have shown positive results. Further reduction in the production cost of phytase is also being pursued. Several studies have already investigated the use of various yeast expression systems as an alternative to the current production method for phytase using overexpression in filamentous fungi. Expression in plants is underway as a means to commercially produce phytase, as in biofarming in which plants such as alfalfa are used as "bioreactors," and also by developing plant cultivars that would produce enough transgenic phytase so that additional supplementation of their grain or meals is not necessary. Ultimately, transgenic poultry and hogs may produce their own digestive phytase. Another active area of current phytase research is expanding its usage. One area that offers tremendous opportunity is increasing the use of phytase in aquaculture. Research is currently centered on utilizing phytase to allow producers in this industry to switch to lower-cost plant protein in their feed formulations. Development of a phytase for this application could significantly lower production costs. Other areas for expanded use range from the use of phytase as a soil amendment, to its use in a bioreactor to generate specific myo-inositol phosphate species. The transformation of phytase into a peroxidase may lead to another novel use for this enzyme. As attempts are made to widen the use of phytase, it is also important that extended exposure and breathing its dust be avoided as prudent safety measures to avoid possible allergic responses. In expanding the use of phytase, another important consideration has been achieved. Conservation of the world's deposits of rock phosphate is recognized as important for future generations. Phosphorus is a basic component of life like nitrogen, but, unlike nitrogen, phosphorus does not have a cycle to constantly replenish its supply. It is very likely that the use of phytase will expand as the need to conserve the world's phosphate reserves increases.

Phytase activity in Aspergillus fumigatus isolates

Extracellular phytase from Aspergillus fumigatus isolates was characterized and their genes were cloned and sequenced. Based on their banding pattern in SDS-PAGE all phytases were found to be glycosylated and have similar molecular mass. A correlation between lower optimum pH (4.0) and a higher optimum temperature (70 degrees C) was found in these enzymes. All enzymes characterized displayed a lower specific activity for phytic acid and were more susceptible to proteolytic degradation than the Aspergillus niger phytase that is now commercially available. DNA sequencing established almost no sequence variation in any of the genes and no correlation is evident between a specific amino acid sequence and any physicochemical and catalytic properties of the enzymes. Despite two of the isolates having identical deduced amino acid sequence, characterization of the enzymes encoded by these two identical genes revealed differences in both pH and temperature optimum. This suggests that differences in pH and temperature optimum in these four isolates of A. fumigatus may be due in part to subtle differences in posttranslational modification.

Biochemical characterization of cloned Aspergillus fumigatus phytase (phyA)

The gene for Aspergillus fumigatus phytase (phyA) was cloned and expressed in Pichia pastoris. The enzyme expressed was purified to near homogeneity using sequential ion-exchange chromatography and was characterized biochemically. Although A. fumigatus phytase shows 66.2% sequence homology with A. ficuum phytase, the most widely studied enzyme, the cloned phytase showed identical molecular weight and temperature optima profile to the benchmark phytase. The pH profile of activity and kinetic parameters, however, differed from A. ficuum phytase. The cloned enzyme contains the septapeptide RHGARYP motif, which is also identical to the active site motif of A. ficuum phytase. Chemical probing of the active site Arg residues using both cyclohexanedione and phenylglyoxal resulted in the inactivation of phytase. The cloned A. fumigatus phytase, however, was more resistant to phenylglyoxal-induced inactivation. Both cloned A. fumigatus and A. ficuum phytases were identically affected by cyclohexanedione. Both the thermal characterization data and kinetic parameters of cloned and expressed A. fumigatus phytase indicate that this biocatalyst is not superior to the benchmark enzyme. The sequence difference between A. fumigatus and A. ficuum phytase may explain why the former enzyme catalyzes poorly compared to the benchmark enzyme. In addition, differential sensitivity toward the Arg modifier, phenylglyoxal, indicates a different chemical environment at the active site for each of the phytases.

Conjugation and modeled structure/function analysis of lysozyme on glycine esterified cotton cellulose-fibers

The antimicrobial activity of lysozyme covalently bound to glycine-derivatized cotton cellulose was assessed in a 96-well format. Lysozyme was immobilized on glycine-bound cotton through a carbodiimide reaction. The attachment to cotton fibers was made through both a single glycine and a glycine dipeptide esterified to cotton cellulose. Higher levels of lysozyme incorporation were evident in the diglycine-linked cotton cellulose samples. The antibacterial activity of the lysozyme-conjugated cotton cellulose against Bacillus subtilis was assessed as a suspension of pulverized cotton fibers in microtiter wells. Inhibition of B. subtilis growth was observed to be optimal within a range of 0.14-0.3 mM (equivalent to 4-20 mg of lysozyme-bound cotton/mL) of lysozyme. Enhancement of activity over soluble lysozyme may result from the solid-phase protection afforded by the cellulose linkage of the glycoprotein against proteolytic lysis. Computational models of lysozyme based on its crystal structure attached through aspartate, glutamate, and COOH-terminal residues to cellopentaose-(3) Gly-O-6-glycyl-glycine ester were constructed. The models demonstrate no steric constraints to the active-site cleft from the glycine-conjugated cellulose chain when lysozyme is bound at the carboxylates of Asp-87, Glu-7, Asp-119, Asp-18, and COOH-terminal Leu-129. The more robust antibacterial activity of the enzyme when bonded to cotton fibers suggests good potential for biologically active enzymes on cotton-based fabrics.

Characterization of recombinant fungal phytase (phyA) expressed in tobacco leaves

The phyA gene from Aspergillus ficuum coding for a 441-amino-acid full-length phytase was expressed in Nicotiana tabacum (tobacco) leaves. The expressed phytase was purified to homogeneity using ion-exchange column chromatography. The purified phytase was characterized biochemically and its kinetic parameters were determined. When the recombinant phytase was compared with its counterpart from Aspergillus ficuum for physical and enzymatic properties, it was found that catalytically the recombinant protein was indistinguishable from the native phytase. Except for a decrease in molecular mass, the overexpressed recombinant phytase was virtually the same as the native fungal phytase. While the temperature optima of the recombinant protein remain unchanged, the pH optima shifted from pH 5 to 4. The results are encouraging enough to open the possibility of overexpressing phyA gene from Aspergillus ficuum in other crop plants as an alternative means of commercial production of this important enzyme.

Identification of a histidine acid phosphatase (phyA)-like gene in Arabidopsis thaliana

A close examination of the protein sequence encoded by the Arabidopsis thaliana gene F21M12.26 reveals the gene product to be a phosphomonoesterase, acid optimum (EC 3.1.3.2). A subclass of this broad acid phosphatase is also known as 'histidine acid phosphatase. ' This is the first sequence-based evidence for a 'histidine acid phosphatase' in a dicotyledon. One important member of this class of enzymes is Aspergillus niger (ficuum) phytase, which came into prominence for its commercial application as a feed additive. The putative protein from A. thaliana gene F21M12.26 shares many important features of Aspergillus phytase, namely, size, active-site sequence, catalytic dipeptide and ten cysteine residues located in the key areas of the molecule, but lacks all nine N-glycosylation sites.

Myo-inositol hexasulfate is a potent inhibitor of Aspergillus ficuum phytase

Myo-inositol hexasulfate (MIHS), a structural analog of the substrate myo-inositol hexaphosphate, is a potent competitive inhibitor of both phyA and phyB enzymes. The Ki of inhibition for the phyA and phyB proteins were estimated to be 4.6 and 0.2 microM, respectively. Thus, the phyB protein is 23-fold more sensitive to MIHS inhibition than the phyA protein. The active-site geometry of phyB protein is presumed to be very different from the phyA protein as deduced by chemical probing of the enzymes by Arg-specific modifiers, i.e., 1,2-cyclohexanedione and phenylglyoxal. Probing the catalytic site of the same proteins by this newly developed specific inhibitor also gives a similar conclusion.

Conservation of the active site motif in Aspergillus niger (ficuum) pH 6.0 optimum acid phosphatase and kidney bean purple acid phosphatase

Aspergillus niger (ficuum) and the kidney bean purple acid phosphatases retained all the essential amino acids in the active site despite a low degree of total sequence homology. This high degree of homology in the sequence motif of A. niger fungal acid phosphatase (Apase6) active site with Kidney bean metallo phosphoesterase (KBPAP) and the absence of the RHG-XRXP sequence motif indicates Apase6 to be a metallophosphoesterase rather than a histidine acid phosphatase.

Differences in the active site environment of Aspergillus ficuum phytases

While Aspergillus ficuum phytaseA (phyA) was rapidly inactivated by 1,2-cyclohexanedione and phenylglyoxal, both specific modifiers of arginine, phytaseB (phyB) showed a markedly different behavior. First, phyB was totally insensitive to 1,2-cyclohexanedione even in the presence of 0.2 M guanidinium hydrochloride; second, the enzyme showed a great deal of resistance to inactivation by phenylglyoxal. Taken together, these results indicate that the chemical environment of the active site of phyB is very different from that of the active site of phyA. Despite sequence similarities of the active site region in these two proteins, their differential behavior to arginine modifiers indicates that other parts of the protein play a role in the active site formation. We expected some differences in the structure since the proteins have dissimilar kinetic parameters and pH optima.

Disulfide bonds are necessary for structure and activity in Aspergillus ficuum phytase

The function of disulfide bonds in Aspergillus ficuum phytase was elucidated by unfolding studies, using guanidinium hydrochloride (Gu.HCl) as denaturant. Although the enzyme is totally inactivated by 0.8 M Gu.HCl, at pH 5.0, the active conformation is instantaneously restored by 0.6 M Gu.HCl, at pH 5.0. Conditions which would permit refolding of phytase are completely negated by 10 mM beta-mercaptoethanol and causes its catalytic demise at pH 7.5. Assay of free thiols using Ellman's reagent indicates that none of the thiols in the ten cysteines in phytase are free; five disulfide bonds were predicted for the enzyme. Sequence comparison of mold phytases and yeast acid phosphatases indicates four conserved cysteines. Thus, disulfide bonds play an important role in the folding of fungal phytase; any perturbation of the process of its formation causes an altered three-dimensional structure that is inconsistent with catalytic activity.

Phytase

Of all the sources of phytase that have been studied (plant, animal, and microorganisms), the highest yields are produced by a wild-type strain A. niger NRRL 3135 (12.7 mg P/hr/ml = 6.8 microns P/ml/min = 113.9 nKat/ml) in a mineral salt medium in which total phosphate (4 mg %) is limiting for growth and cornstarch and glucose are the carbon sources. Synthesis of the enzyme is repressed by phosphate in the wild-type strain. Aspergillus niger NRRL 3135 produces two phytases one with pH optima at 2.5 and 5.5 (phyA) and one with an optimum at pH 2.0 (phyB). It also produces a pH 6.0 optimum phosphatase that has no phytase activity. These three glycoproteins have been purified to homogeneity, characterized, sequenced, and cloned. The sequences have been compared to each other, other phytases, and to known phosphatases. Their homology has been determined. The active sites of phytases show remarkable homology to the active site residues of the members of a particular class of acid phosphatase (histidine phosphatase). The most conserved sequence is RHGXRXP. Phytase has been covalently immobilized on Fractogel TSK HW-75 F and glutaraldehyde-activated silicate. It has been immobilized on agarose. Losses of activity have been noted on immobilization but these may be minimized by future research. It should be possible to commercially produce and recover penta-, tetra-, tri-, di-, and monoinositol phosphates using immobilized phytase if markets develop for those products. Phytase (phyA) from A. niger NRRL 3135 has been cloned into an A. niger glucoamylase producing strain CBS 513.88 using a construct that has a glucoamylae promoter and an A. niger NRRL 3135 leader sequence, and that is devoid of phosphate repression. The yield of the secreted enzyme was increased 52-fold above that of wild-type A. niger NRRL 3135. The bioengineered organism produces 270 microns P/ml/min (4500 nKat/ml) which is approximately 7.9 g/liter in the medium. The yield of the secreted enzyme was increased 1440-fold above that of wild type CBS 513.88. Commercial preparations of the cloned enzyme are available. Phytase (phyA) has been cloned into tobacco and canola. The enzyme is localized in the seed and expressed at high levels. Feeding of the seed to animals has made the phytin-P in the commercial diets available to the animals. The efficacy of feeding phytase to monogastric animals (poultry and swine) has been established. The amount of enzyme that is necessary to be added to commercial diets has been titred for broilers, layers, turkeys, ducks, and swine. The units of enzyme required are related to the phytin-P content in the diet. The use of the enzyme as a feed additive has been cleared in 22 countries. If phytase were used in the diets of all of the monogastric animals reared in the U.S., it would release phosphorus that has a value of $1.68 x 10(8) per year. The FDA has approved the enzyme preparation as GRAS. The effect of feeding phytase to animals enables assimilation of the P found in feed ingredients and diminishes the amount of phosphate in the manure and subsequently entering the environment. The effect of feeding phytase to animals on pollution has been quantitatively determined. If phytase were used in the diets of all of the monogastric animals reared in the United States, it would preclude 8.23 x 10(7) kg P from entering the environment.

The Aspergillus niger (ficuum) aphA gene encodes a pH 6.0-optimum acid phosphatase

We have used the Aspergillus niger (An) aphA gene as a probe and cloned the A. ficuum (Af) SRRC 265 gene encoding an extracellular pH 6.0-optimum acid phosphatase (APase6) from a genomic library. The identity of the Af aphA gene was confirmed and its nucleotide (nt) sequence verified by comparing its deduced amino acid (aa) sequence to that of purified Af APase6. A comparison of the nt sequences of the An and Af genes suggested that errors were made in the previously reported An aphA sequence. Several regions of the An aphA were resequenced and the mistakes corrected. With its nt sequence corrected, the An aphA is nearly identical to the cloned Af gene encoding APase6, and in 90.4% agreement in the coding regions. Both genes have three conserved introns and when translated, both nt sequences code for a polypeptide of 614 aa. There is now evidence that the two cloned genes are homologous and code for acid phosphatases that are 96% identical.

Purification and some properties of inositol 1,3,4,5,6-Pentakisphosphate 2-kinase from immature soybean seeds

Inositol 1,3,4,5,6-pentakisphosphate 2-kinase was purified from immature soybean seeds harvested approximately 5 weeks post-anthesis. A crude extract was clarified using polyethyleneimine and purified by chromatography on DEAE-cellulose, Cibacron Blue 3GA-agarose, Toyopearl DEAE 650M, and Toyopearl phenyl 650M columns. The enzyme had a relative molecular mass, M(r), of 52,000 as determined by sodium dodecyl sulfate-poly-acrylamide gel electrophoresis and retained 50% of its activity after 6 weeks at 0 degrees C. The Km values for inositol 1,3,4,5,6-pentakisphosphate and MgATP, respectively, were 2.3 microM and 8.4 microM, and the Vmax was 243 nmol/min/mg. The pH and temperature optima, respectively, were 6.8 and 42 degrees C. Maximum activity was obtained when the magnesium ion concentration was 4 mM. The kinase specifically phosphorylated the 2-position on the inositol ring and could also utilize D-inositol 1,4,5,6-tetrakisphosphate as a substrate. The K for the reaction was 14, indicating that the enzyme may be involved in both inositol hexakisphosphate formation in maturing seeds and ATP resynthesis in germinating seeds. Substrate concentrations in mature seeds were favorable for ATP formation, whereas additional factors appeared to drive the accumulation of inositol hexakisphosphate in maturing seeds.

An acid phosphatase from Aspergillus ficuum has homology to Penicillium chrysogenum PhoA

Three secreted acid phosphatases had previously been characterized from Aspergillus ficuum grown under conditions of limited phosphate. One of these could not be readily separated from AFPhyB, a pH 2.5 optimum acid phosphatase with phytase activity. From extensive protein sequence analysis and subsequent cloning of the gene, we have shown that the AFPhyB protein fraction contains a fourth secreted acid phosphatase (AFPhoA) that has 64% homology to a phosphate-repressible acid phosphatase from Penicillium chrysogenum. Garnier plot analysis revealed that the putative phosphate catalytic domain of AFPhoA at His215Asp216 is similar to those of other acid phosphatases, but that AFPhoA lacks the phosphate-binding motif RHGXRXP of known histidine phosphatases.

The complete primary structure elucidation of Aspergillus ficuum (niger), pH 6.0, optimum acid phosphatase by Edman degradation

The primary structure of the Aspergillus ficuum (niger) NRRL 3135 extracellular, pH 6.0, optimum acid phosphatase (E.C.3.1.3.2) was elucidated by gas phase sequencing. It was deduced by sequence overlap of peptides obtained from trypsin, chymotrypsin, clostripain, and cyanogen bromide digests of the pyridylethylated protein. The mature, active protein is composed of 583 amino acids, including 13 glycosylated Asn residues. The unglycosylated protein has a MW of 64,245-KDa and a pI of 4.97. Two putative metal binding sites were identified in the molecule. This enzyme may represent a special class of high molecular weight acid phosphatase, since it lacks the active site sequence RHGXRXP and shows no significant homology with known acid phosphatases containing this active site. Homology to human type 5 and A.niger APases was detected, however.

Identification and cloning of a second phytase gene (phyB) from Aspergillus niger (ficuum)

An Aspergillus niger (ficuum) genomic DNA lambda EMBL3 library was probed with a 354-bp DNA fragment obtained by polymerase chain reaction of A. niger DNA with oligonucleotides based on partial amino acid sequence of a pH 2.5 optimum acid phosphatase. A clone containing a 1605 bp segment (phyB) encoding the 479 amino acid enzyme was isolated and found to contain four exons. Global alignment revealed 23.5% homology to Aspergillus niger phytase (PhyA); four regions of extensive homology were identified. Some of these regions may contain catalytic sites for phosphatase function.

Identification of active-site residues in Aspergillus ficuum extracellular pH 2.5 optimum acid phosphatase

Primary structure elucidation of peptides generated by cyanogen bromide, endoproteinase Glu-C, and clostripain cleavage of an Aspergillus ficuum extracellular pH optimum 2.5 acid phosphatase identified a region which contains the active site of the enzyme. The 23-residue segment contains the fragment RHGXRXP, which is homologous to acid phosphatase from Saccharomyces spp., Aspergillus ficuum, mammals, and bacteria. Homologous or conservative substitutions are observed in the 10-amino acid fragment preceding this region.

Aspergillus ficuum phytase: complete primary structure elucidation by chemical sequencing

The primary structure of Aspergillus ficuum phytase was deduced from overlaps in peptide sequences. The unglycosylated enzyme is a 441 residue protein with a molecular mass of 48.5-KDa, as calculated from the total covalent structure. The estimated pl of the protein is about 4.76. Of the 19 Asn residues, 9 were found to be glycosylated. The phytase consists of 37% non-polar, 42% polar, 11.5% acidic, and 9.5% basic amino acids. The putative active site of the enzyme containing the sequence RHG is located at the N-terminal region of the molecule and shows homology to the active site of both microbial and mammalian acid phosphatases, and phosphoglycerate mutase.

Purification of a 40-kilodalton methyltransferase active in the aflatoxin biosynthetic pathway

The penultimate step in the aflatoxin biosynthetic pathway of the filamentous fungi Aspergillus flavus and A. parasiticus involves conversion of sterigmatocystin to O-methylsterigmatocystin. An S-adenosylmethionine-dependent methyltransferase that catalyzes this reaction was purified to homogeneity (> 90%) from 78-h-old mycelia of A. parasiticus SRRC 163. Purification of this soluble enzyme was carried out by five soft-gel chromatographic steps: cell debris remover treatment, QMA ACELL chromatography, hydroxylapatite-Ultrogel chromatography, DEAE-Spherodex chromatography, and Octyl Avidgel chromatography, followed by MA7Q high-performance liquid chromatography. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the protein peak from this step on silver staining identified a single band of approximately 40 kDa. This purified protein was distinct from the dimeric 168-kDa methyltransferase purified from the same fungal strain under identical growth conditions (D. Bhatnagar, A. H. J. Ullah, and T. E. Cleveland, Prep. Biochem. 18:321-349, 1988). The chromatographic behavior and N-terminal sequence of the 40-kDa enzyme were also distinct from those of the 168-kDa methyltransferase. The molar extinction coefficient of the 40-kDa enzyme at 278 nm was estimated to be 4.7 x 10(4) M-1 cm-1 in 50 mM potassium phosphate buffer (pH 7.5).

Positive identification of a lambda gt11 clone containing a region of fungal phytase gene by immunoprobe and sequence verification

As the initial step in a project to provide a more cost-effective source of the phytase enzyme, this paper reports on the use of a polyclonal antibody raised to phytase purified from an isolate of Aspergillus niger (A. ficuum) to screen an A. niger lambda gt11 expression library and the use of amino acid sequencing to identify a clone containing part of the fungal phytase gene. The described use of amino acid sequence fragments to verify the cloning of a gene has potential applications in other cloning projects.

Cyclohexanedione modification of arginine at the active site of Aspergillus ficuum phytase

Reaction of Aspergillus ficuum phytase with the arginine specific modifier 1,2-cyclohexanedione causes a rapid loss of activity. The inactivation can be partially reversed by 0.2 M hydroxylamine and exhibits pseudo-first order kinetics. The reaction order and second order rate constant of inactivation were 0.87 and 6.72 M-1 Min-1, respectively. Amino acid analysis of modified phytase indicates that about 7 arginine of the total 19 were modified. While the chymotryptic maps of treated and untreated phytase wer virtually identical, the tryptic maps had 4 peaks of altered mobility. An Arg containing tripeptide was identified in the phytase which is also present in other phosphohydrolases and may represent one of the labile Arg involved in the formation of the active site.

Extracellular alpha galactosidase (E.C. 3.2.1.22) from Aspergillus ficuum NRRL 3135 purification and characterization

Extracellular alpha-galactosidase, a glycoprotein from the extracellular culture fluid of Aspergillus ficuum grown on glucose and raffinose in a batch culture system, was purified to homogeneity in five steps by ion exchange and hydrophobic interaction chromatography. The molecular mass of the enzyme was 70.8 Kd by SDS polyacrylamide gel electrophoresis and 74.1 Kd by gel permeation HPLC. On the basis of a molecular mass of 70.7 Kd, the molar extinction coefficient of the enzyme at 279 nm was estimated to be 6.1 X10(4) M-1 cm-1. The purified enzyme was remarkably stable at 0 degrees C. It had a broad temperature optimum and maximum catalytic activity was at 60 degrees C. It retained 33% of its activity after 10 min. at 65 degrees C. It had a pH optimum of 6.0. It retained 62% of its activity after 12 hours at pH 2.3. The Kms for p-nitrophenyl-alpha-D-galactopyranoside, o-nitrophenyl-alpha-D-galactopyranoside and m-nitrophenyl-alpha-D-galactopyranoside are: 1462, 839 and 718 microM. The enzyme was competitively inhibited by mercury (19.8 microM), silver (21.5 microM), copper (0.48 mM), zinc (0.11 mM), galactose (64.0 mM) and fructose (60.3 mM). It was inhibited non-competitively by glucose (83.2 mM) and uncompetitively by mannose (6.7 mM).

High-performance liquid chromatography separation of nikkomycins X and Z

A reversed-phase, C-18 HPLC method for separation, with baseline resolution, of the chitin synthase inhibitors nikkomycin X and Z is described. This permits, for the first time, satisfactory identification of nikkomycin X and Z contained in a mixture. The use of 30 mM ammonium formate (pH 4.7) containing the ion-pair agent heptanesulfonic acid (1 mM) was critical for the successful separation of these fungicides.

Aspergillus ficuum phytase: partial primary structure, substrate selectivity, and kinetic characterization

Purified Aspergillus ficuum phytase's partial primary structure and amino acid and sugar composition were elucidated. Determination of kinetic parameters of the enzyme at different pH values and temperatures indicated no significant alteration of the Km for phytate while the Kcat was affected. The enzyme was able to release more than 51% of the total available Pi from phytate in a 3.0 hr assay at 58 degrees C, but the Kcat dropped to 15% of the initial rate. Substrate selectivity studies revealed phytate to be the preferred substrate. The pH optima of phytase was 5.0, 4.0, and 3.0 for phytate, ATP, and polyphosphate, respectively. The enzyme had varied sensitivity towards cations. While Ca++ and Fe++ produced no effect on the catalytic rate of the enzyme, Cu+, Cu++, Zn++, and Fe were found to be inhibitory. Mn++ was observed to enhance enzyme activity by 33% at 50 microM. Known inhibitors of acid phosphatases e.g. L (+)-tartrate, phosphomycin, and sodium fluoride had no effect on enzyme activity.

Immobilization of Aspergillus ficuum phytase: product characterization of the bioreactor

Aspergillus ficuum phytase was covalently immobilized on Fractogel TSK HW-75 containing 2-oxy-l-alkylpyridinium salts. A packed-bed bioreactor was constructed with the immobilized phytase. An HPLC ion-exchange method was used to analyze the enzymatic products of the bioreactor. Immobilized fungal phytase was able to hydrolyze myo-inositol Hexa-, penta-, tetra-, tri-, and diphosphates. When the substrate solution was recirculated for 5 hr in the bioreactor about 50% inorganic orthophosphate was released and myo-inositol-diphosphate and mono-phosphate were the only remaining products.

Production, rapid purification and catalytic characterization of extracellular phytase from Aspergillus ficuum

A rapid purification scheme utilizing three chromatographic steps resulted in 6 fold purification of Aspergillus ficuum phytase (myo-inositol-hexakisphosphate 3-phosphohydrolase, EC 3.1.3.8). At pH 5.0 and 60 degrees C the enzyme performed acceptably for 2.0 hr with only 30% diminished catalytic rate at the end. Substrate concentration exceeding 2mM was inhibitory. The inorganic orthophosphate, the product and a weak inhibitor, exhibited a Ki of 1.9 x 10(-3)M. The extracellular phytase has the potential for industrial use since it can be over produced, easily purified, remain catalytically active for a longer period and is not subjected to severe product inhibition.

Extracellular PH 2.5 optimum acid phosphatase from Aspergillus ficuum: immobilization on modified fractogel

Aspergillus ficuum pH 2.5 optimum acid phosphatase (orthophosphoric monoesters phosphohydrolase, E.C.3.1.3.2) was covalently immobolized on 2-fluoro-1-methylpyridinium toluene-4-sulfonate (FMP)-activated Fractogel TSK HW-50F. The catalytic parameters and stability of the immobilized enzyme were compared with those of the free enzyme. While the Km and the temperature optima were unchanged, the Ki for orthophosphate was changed from 185 microM to 422 microM and greater stability was observed against heat treatment.

Mutation affecting peptide bond formation in nikkomycin biosynthesis

Nikkomycin, a nucleoside-peptide analog of UDP-N-acetylglucosamine, is a potent chitin synthase inhibitor produced by the bacterium Streptomyces tendae. The HPLC profile of fermentation products in culture broths of a non-producing mutant, Nik 15, was compared with nikkomycin standards. Nikkomycin C and D, the glycone and aglycone moieties, respectively, of nikkomycin Z accumulated. This indicates the mutation affects the capacity to form a peptide bond between nikkomycin C and D, which is here proposed to be the terminal step in the synthesis of the biologically active nikkomycin Z. This is also the first documented case of a mutation affecting a specific step in nikkomycin biosynthesis.

Purification and characterization of a methyltransferase from Aspergillus parasiticus SRRC 163 involved in aflatoxin biosynthetic pathway

A five step scheme has been developed for the purification of a methyltransferase (MT) from mycelia of 3-day old Aspergillus parasiticus (SRRC 163), which catalyzes one step in the aflatoxin biosynthetic pathway. The S-adenosylmethionine (SAM) requiring MT activity is essential for the conversion of sterigmatocystin (ST) to O-methylsterigmatocystin (OMST) prior to being converted to aflatoxin B1. The purification of the MT was carried out from cell-free extracts by CDR (Cell Debris Remover, a cellulosic weak anion exchanger, Whatman) treatment, QMA ACELL, Hydroxylapatite-Ultrogel, PBE 94 chromatofocusing and FractoGel TSK HW-50F filtration chromatography. The purified enzyme was only about 0.1% of the total extractable proteins. The pI of the protein was about 5.0 as judged by chromatofocusing. Results of gel filtration chromatography indicated the approximate molecular mass of the native protein to be 160-KDa. SDS-polyacrylamide gel electrophoresis revealed two protein subunit bands of molecular masses approximately 110-KDa and 58-KDa. The molar extinction coefficient of the enzyme at 280 nm was estimated to be 7.87 X 10(4) M-1 cm-1 in 50 mM potassium phosphate buffer (pH 7.5). The reaction catalyzed by the MT was optimum at pH 7.5 and between 25-35 degrees C. The Km of the enzyme for ST and SAM was determined to be 1.8 microM and 42 microM, respectively with an estimated turnover number of the enzyme for ST of 2.2 X 10(-2) per sec.

Purification and characterization of an endonuclease (E.C. 3.1.30.1) from Streptomyces tendae

A single-strand-specific endonuclease which converted negatively supercoiled DNA to open-circular and linear DNA was purified to homogeneity with Hb-Sepharose 4B, DEAE Trisacryl M, HA-Ultrogel and PBE-94 chromatofocusing from extracts of Streptomyces tendae ATCC 31160. Bio-Gel P-200 chromatography and electrophoresis in SDS-PAGE indicated the native protein was a monomer with a molecular weight of approximately 40-kDa. This enzyme did not hydrolyze double-stranded linear DNA but digested RNA and circular single-strand DNA. Sequence specificity for nicking of negatively supercoiled DNA was not detected.

Aspergillus ficuum extracellular pH 6.0 optimum acid phosphatase: purification, N-terminal amino acid sequence, and biochemical characterization

An extracellular acid phosphatase, pH optimum 6.0 from crude culture filtrate of Aspergillus ficuum was purified to homogeneity using cation exchange chromatography and chromatofocusing steps. SDS-PAGE of the purified enzyme exhibited two stained bands at approximately 82-KDa and 70-KDa. The mobility of the active enzyme in gel permeation chromatography indicated the molecular mass to be about 85-KDa. In the concentrated form the enzyme appeared to be purple, the visible absorption spectrum shows a lambda max at 580 nm. On the basis of molecular mass of 82-KDa, the molar extinction coefficient of the enzyme at 280 nm and 580 nm was estimated to be 1.2 x 10(5) M-1 cm-1 and 1.3 x 10(3) M-1 cm-1 respectively. Judging by chromatofocusing, the isoelectric point of the enzyme was about 4.9. The purified enzyme was unstable at 70 degrees C. The enzyme was catalytically very active from 55 degrees to 65 degrees C with a maximum activity at 63 degrees C. The Michaelis constant of the enzyme for p-nitrophenylphosphate was 200 microM with a computed Kcat of 260 per sec. Although the enzyme was insensitive to fluoride, tartrate, and N-ethylmaleimide (NEM), it was competitively inhibited by phosphomycin (Ki = 1.00 mM) and inorganic orthophosphate (Ki = 165 microM). While the enzyme was relatively insensitive to Mn++, Cu++ and Zn++ inhibited the activity 540 fold at a concentration of 100 microM. The enzyme showed positive PAS staining and hence is a glycoprotein (28% glycosylation); the sugar composition suggests the presence of N-linked high mannose-oligosaccharides and galactose. A partial N-terminal amino acid sequence up to the thirty-fourth residue was elucidated.

Purification and characterization of phytase from cotyledons of germinating soybean seeds

Soybean phytase (myo-inositol-hexakisphosphate phosphohydrolase; EC 3.1.3.8) was purified from 10-day-old germinating cotyledons using a four-step purification scheme. Phytase was separable from the major acid phosphatase present, and stained as a minor band of the three acid phosphatases detectable by activity staining after gel electrophoresis. The purified enzyme exhibited two closely migrating bands on sodium dodecyl sulfate-polyacrylamide gel electrophoresis of approximately 59 and 60 KDa. The molar extinction coefficient of the enzyme at 280 nm was estimated to be 7.5 X 10(4) M-1 cm-1. The isoelectric point of phytase, as judged by the elution profile on chromatofocusing, was about 5.5. The enzyme was totally absorbed to a Procion Red HE3B column and eluted as a single protein component at a salt concentration of 250-300 mM. The enzyme possessed a high affinity for phytic acid (apparent Km = 48 microM), and was strongly inhibited by phosphate (apparent Ki = 18 microM), vanadate, and fluoride. Characteristic of other plant phytases, the pH and temperature optima were 4.5-4.8 and 55 degrees C, respectively.

Purification and characterization of acid phosphatase from cotyledons of germinating soybean seeds

Soybean acid phosphatase (orthophosphoric-monoester phosphohydrolase, EC 3.1.3.2) was completely separated from phytase (EC 3.1.3.8) isolated from cotyledons of germinating seeds and purified to homogeneity. A four-step purification regimen consisting of ammonium sulfate fractionation, and ion-exchange, affinity, and chromatofocusing gel chromatographies was employed to achieve a homogeneous preparation. Acid phosphatase activity appeared as a major band of the three forms of acid phosphatase identified on native gels. The purified enzyme had a molecular weight of 53,000 when electrophoresed on 8% sodium dodecyl sulfate-polyacrylamide gel electrophoresis and a molecular weight of 53,000 from its mobility in a Fracto-gel TSK HW-50F gel permeation column. The molar extinction coefficient of the enzyme at 278 nm was estimated to be 4.2 X 10(4) M-1 cm-1. The isoelectric point of the protein, as revealed by chromatofocusing, was about 6.7. The optimal pH for activity, like other plant acid phosphatases, was 5.0. While the enzyme failed to accommodate phytate as a substrate, the enzyme did exhibit a broad substrate selectivity. The affinity of the enzyme for p-nitrophenyl phosphate was high (Km = 70 microM), and activity was competitively inhibited by orthophosphate (Ki = 280 microM). The estimated catalytic turnover number (Kcat) of the enzyme for p-nitrophenyl phosphate was about 430 per second. Although the purified enzyme was stable at 0 degrees C and exhibited maximum catalytic activity at 60 degrees C, thermal inactivation studies indicated that the enzyme lost 100% activity after treatment at 68 degrees C for 10 min.

Purification, N-terminal amino acid sequence and characterization of pH 2.5 optimum acid phosphatase (E.C. 3.1.3.2) from Aspergillus ficuum

An acid phosphatase from crude culture filtrate of Aspergillus ficuum was purified to homogeneity using three ion exchange chromatographic steps. SDS-PAGE of the purified enzyme gave a single stained band at approximately 68-KDa. The mobility of the native enzyme in gel filtration chromatography, however, indicated that the molecular mass to be about 130-KDa implying the active form to be a dimer. On the basis of a molecular mass of 68-KDa, the molar extinction coefficient of the enzyme at 280 nm was estimated to be 3.4 x 10(5) M-1 cm-1. The isoelectric point of the enzyme, as judged by chromatofocusing, was about 4.0. The purified enzyme is highly stable at 0 degree C. Thermal inactivation studies have indicated that the enzyme is unstable at 70 degrees C. The enzyme, however, exhibited a broad temperature optima with a maximum catalytic activity at 63 degrees C. The Km of the enzyme for p-nitrophenylphosphate is about 270 microM with an estimated turnover number of 2550 per sec. The enzyme is a glycoprotein as evidenced by the positive PAS staining; the sugar composition suggests the presence of N-linked high mannose-oligosaccharides. A partial N-terminal amino acid sequence up to the twenty-third residue was obtained. The enzyme was inhibited competitively by inorganic orthophosphate (Ki = 185 microM) and non-competitively by phosphomycin (Ki = 600 microM).

Extracellular phytase (E.C. 3.1.3.8) from Aspergillus ficuum NRRL 3135: purification and characterization

Extracellular phytase from Aspergillus ficuum, a glycoprotein, was purified to homogeneity in 3 column chromatographic steps using ion exchange and chromatofocusing. Results of gel filtration chromatography and SDS-polyacrylamide gel electrophoresis indicated the approximate molecular weight of the native protein to be 85-100-KDa. On the basis of a molecular weight of 85-KDa, the molar extinction coefficient of the enzyme at 280 nm was estimated to be 1.2 X 10(4) M-1 cm-1. The isoelectric point of the enzyme, as deduced by chromatofocusing, was about 4.5. The purified enzyme is remarkably stable at 0 degree C. Thermal inactivation studies have shown that the enzyme retained 40% of its activity after being subjected to 68 degrees C for 10 minutes, and the enzyme exhibited a broad temperature optimum with maximum catalytic activity at 58 degrees C. The Km of the enzyme for phytate and p-nitrophenylphosphate is about 40 uM and 265 uM, respectively, with an estimated turnover number of the enzyme for phytate of 220 per sec. Enzymatic deglycosylation of phytase by Endoglycosidase H lowered the molecular weight of native enzyme from 85-100-KDa to about 76-KDa; the digested phytase still retained some carbohydrate as judged by positive periodic acid-Schiff reagent staining of the electrophoresed protein. Immunoblotting of the phytase with monoclonal antibody 7H10 raised against purified native enzyme recognized not only native but also partially deglycosylated protein.

Purification and characterization of Bacillus subtilis methyl-accepting chemotaxis protein methyltransferase II

A Bacillus subtilis methyltransferase capable of methylating membrane-bound methyl-accepting chemotaxis proteins (MCPs) of a chemotaxis mutant was purified to homogeneity. MCPs are normally unmethylated in this strain. Results of gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis indicate that the enzyme is a 30,000 molecular weight monomer. The enzyme transfers methyl groups from S-adenosylmethionine to glutamate residues of the substrates. The enzyme is activated by divalent cations and has a Km for S-adenosylmethionine of about 5 microM. It is competitively inhibited by S-adenosylhomocysteine, with a Ki of about 0.2 microM, and exhibits an in vitro assay pH optimum of 6.9. This methyltransferase is very different from another methyltransferase from B. subtilis, described previously (Ullah, A. H. J., and Ordal, G. W. (1981) Biochem. J. 199, 795-805).

Purification and characterization of methyl-accepting chemotaxis protein methyltransferase I in Bacillus subtilis

A methyltransferase that methylates one of the proteins involved in chemotactic adaptation to sensory stimuli in Bacillus subtilis was purified to homogeneity. The enzyme utilizes S-adenosylmethionine as donor for a methyl group that is transferred to a glutamate residue in a 69 000-mol.wt. membrane protein and also to a protein of 19 000 mol.wt. The molecular weights of the denatured enzyme by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis and of the native enzyme by gel-filtration chromatography both show the protein to be a 44 000-mol.wt. monomer. Isoelectric focusing of the purified methyltransferase showed the protein to be a single species with isoelectric point pI 5.4. On the basis of a molecular weight of 44 000, the molar absorption coefficient at 262 nm of the enzyme is 10.9 x 10(4) M-1 . cm-1. The Km of the enzyme for S-adenosylmethionine is about 2 microM. The Ki for S-adenosylhomocysteine is about 0.2 microM. Ca2+ is a competitive inhibitor of methylation, with a Ki of 0.065 microM. The enzyme methylates membranes from the wild-type more efficiently than membranes isolated from a mutant strain defective in chemotaxis. The enzyme is unable to methylate Escherichia coli membranes.

In vivo and in vitro chemotactic methylation in Bacillus subtilis

Two doublets of Bacillus subtilis membrane proteins with molecular weights of 69,000 and 71,000 and of 30,000 and 30,800, were labeled by C3H3 transfer in the absence of protein synthesis. In addition, there was intense methylation of several low-molecular-weight substances. Both doublets were missing in a chemotaxis mutant. The equivalent proteins in Escherichia coli and Salmonella typhimurium are believed to be the methyl-accepting chemotaxis proteins. The higher-molecular-weight doublet bands were increased in degree of methylation upon addition of attractant to the bacteria. A methyltransferase from B. subtilis that methylates the wild-type membrane significantly better than the mutant membrane, using S-adenosylmethionine, has been partly purified. The methylated product was alkali labile and is probably a gamma-glutamyl methyl ester, as in E. coli and S. typhimurium. Ca2+ ion inhibited the methyltransferase, with a Ki of about 80 nM. Analysis of the in vitro methylation product showed labeling of the 69,000-dalton methyl-accepting chemotaxis protein and a low-molecular-weight protein, using wild-type membrane. Labeling of the low-molecular-weight protein but not of the 69,000 dalton protein was observed when the mutant membrane was used. The chemotaxis mutant tumbled much longer than the wild type when diluted away from attractant.

Mycoplasma phosphoenolpyruvate-dependent sugar phosphotransferase system: purification and characterization of the phosphocarrier protein

The Mycoplasma phosphoenolpyruvate-dependent sugar phosphotransferase system consists of three components: a membrane-bound enzyme II, a soluble enzyme I, and a soluble phosphocarrier protein, HPr. The HPr has been purified to homogeneity by a combination of ammonium sulfate precipitations, gel filtration and diethylaminoethyl, carboxymethyl Bio-Gel A, and hydroxylapatite column chromatography. The purified protein is relatively heat stable (ca. 50% activity survives 30 min of boiling) and has a molecular weight of ca. 10,000 (determined by sodium dodecyl sulfate-gel electrophoresis and amino acid analysis). It contains a single histidine residue per molecule and can be totally inactivated by photooxidation with Rose Bengal dye. Although the mycoplasma HPr is very similar to that of Escherichia coli, it shows no significant association with antiserum produced against E. coli HPr.