Glycerol catabolism in Aspergillus nidulans

Glycerol is catabolized in Aspergillus nidulans by glycerol kinase and a mitochondrial FAD-dependent sn-glycerol 3-phosphate dehydrogenase. The levels of both enzymes are controlled by carbon catabolite repression and by specific induction. Biochemical and genetical analyses show that dihydroxyacetone and D-glyceraldehyde are converted into glycerol and then catabolized by the same pathway. D-Glyceraldehyde can be reduced by NADP(+)-dependent glycerol dehydrogenase or by alcohol dehydrogenase I, while dihydroxyacetone is only reduced by the first enzyme. Three new glycerol non-utilizing mutants have been found. These three mutations define three hitherto unknown loci, glcE, glcF and glcG. The mutation in glcG leads to a greatly decreased sn-glycerol-3-phosphate dehydrogenase activity.

Neoglycoproteins as carriers for antiviral drugs: synthesis and analysis of protein-drug conjugates

In order to investigate whether neoglycoproteins can potentially act as carriers for targeting of antiviral drugs to certain cell types in the body, various neoglycoproteins were synthesized using thiophosgene-activated p-aminophenyl sugar derivatives. These neoglycoproteins were conjugated with the 5'-monophosphate form of the antiviral drug AZT. For a proper characterization of these preparations, both protein and drug content have to be determined. Comparison of the Lowry and the Bio-Rad protein assays revealed that for both the neoglycoprotein carriers themselves and the AZTMP conjugates, the Lowry assay yielded the most reliable and reproducible results. It was demonstrated that both the reagent used for drug conjugation (ECDI) as well as the introduction of phenyl-sugar groups in the protein interfered with the analysis of bound nucleotide as based on spectral differences between protein and protein-drug conjugate. Therefore, we developed a rapid HPLC system for determination of the drug-protein coupling ratio through acid hydrolysis of the covalently bound nucleotide. With the ECDI-mediated conjugation of 5'-monophosphate drug derivatives to neoglycoproteins, products with molar ratios of drug to protein ranging from 1.2 to 5.6 were obtained. The drug-neoglycoprotein conjugates appeared to be fairly stable during storage, in lyophilized form, at -20 degrees C. The anti-HIV-1 activity of the neoglycoprotein-drug conjugates, as determined in vitro in MT-4 cells, was shown to be dependent on glycosylation of the albumin and also on the kind of sugar present in the neoglycoprotein. The anti-HIV-1 activity of the AZTMP-mannose-albumin conjugate exceeded that of the parent drug by more than 4 times.

Genetic localization of a series of genes affecting glucose oxidase levels in Aspergillus niger

A number of mutants of Aspergillus niger, affected in glucose oxidase (GOX) expression, are described. The overproducing mutants could be classified into seven complementation groups whereas two glucose oxidase-negative complementation groups were recognized. These nine gox loci were assigned to linkage groups using master strains with marked chromosomes. Three gox loci are in linkage group II, one is in III, two are in V and two are in linkage group VII. One weak glucose oxidase-overproducing mutant could not be assigned to one of the linkage groups. These genetically well characterized mutants will be used in a strain improvement program based on genetic recombination.

The pharmacokinetics of beta-cyclodextrin and hydroxypropyl-beta-cyclodextrin in the rat

Hydroxypropyl-beta-cyclodextrin was analyzed by HPLC using postcolumn complexation with phenolphthalein and negative colorimetric detection, with a detection limit of 20 micrograms/ml. The pharmacokinetics of beta-cyclodextrin and of hydroxypropyl-beta-cyclodextrin were studied after intravenous administration to permanently cannulated rats. The pharmacokinetic behavior of both cyclodextrins was similar to that of inulin, showing rapid distribution over extracellular fluids. Elimination occurred through glomerular filtration. When a dose of 200 mg/kg beta-cyclodextrin was administered the elimination rate was decreased, probably as a result of nephrotoxicity of beta-cyclodextrin. Within 24 hr after administration most of the cyclodextrin dose was recovered unchanged in urine. After oral administration, only insignificant amounts of intact beta-cyclodextrin were absorbed from the gastrointestinal tract.

Molecular cloning, nucleotide sequence and expression of the gene encoding prepro-polygalacturonaseII of Aspergillus niger

PolygalacturonaseII of Aspergillus niger was fragmented using CNBr and the NH2-terminal fragment and another fragment were partially sequenced. The polygalacturonaseII (pgaII) gene was then isolated by using an oligonucleotide mixture based on the internal amino acid sequence as a probe. The nucleotide sequence of the pgaII structural gene was determined. It was found that polygalacturonaseII is synthesized as a precursor having an NH2-terminal prepro-sequence of 27 amino acids. The cloned gene was used to construct polygalacturonaseII over-producing A. niger strains. PolygalacturonaseII was isolated from one such strain and was determined to be correctly processed and to be fully active.

Cloning and expression of a second Aspergillus niger pectin lyase gene (pelA): indications of a pectin lyase gene family in A. niger

Using the previously cloned Aspergillus niger N756 pectin lyase D gene as a probe, the corresponding pelD gene has been isolated from a genomic library of the laboratory strain A. niger N400. This gene encodes PLD, previously described as PLI, which is one of the two major pectin lyases isolated from the commercial pectinase preparation Ultrazym. Heterologous hybridization of the A. niger N400 genomic library with the pelD gene led to the isolation of another five genes: pelA, B, C, E, and F. These genes differ in their hybridization patterns with probes containing either the entire pelD gene, or 5' or 3' parts thereof. By partial sequencing, and expression in an A. niger transformant containing multiple copies of the pelA gene, we show that this gene, which hybridizes strongest with the pelD gene, encodes the other major pectin lyase from Ultrazym, PLII.

A translocation activating the cryptic nitrogen regulation gene areB inactivates a previously unidentified gene involved in glycerol utilisation in Aspergillus nidulans

The chromosome VIII translocation breakpoint of the areB-404 translocation, selected for its ability to activate the cryptic nitrogen metabolism regulatory gene areB, and the mutation glcD-100 both lead to loss of mitochondrial FAD-dependent sn-glycerol-3-phosphate dehydrogenase in Aspergillus nidulans. These two lesions therefore define glcD, a second gene (in addition to glcB) where mutation can result in loss of this enzyme. The glcD gene has been localised to a centromere-proximal region of the right arm of chromosome VIII. Although all six known areB-activating mutations involve chromosomal rearrangements and presumably therefore gene fusions, areB-404 is the first such rearrangement where the gene involved in an areB fusion has been identified.

Characterization of a glycerol kinase mutant of Aspergillus niger

A glycerol-kinase-deficient mutant of Aspergillus niger was isolated. Genetic analysis revealed that the mutation is located on linkage group VI. The phenotype of this mutant differed from that of a glycerol kinase mutant of Aspergillus nidulans in its ability to utilize dihydroxyacetone (DHA). The weak growth on glycerol of the A. niger glycerol kinase mutant showed that glycerol phosphorylation is an important step in glycerol catabolism. The mutant could still grow normally on DHA because of the presence of a DHA kinase. This enzyme, probably in combination with an NAD(+)-dependent glycerol dehydrogenase, present only in the mutant, is responsible for the weak growth of the mutant on glycerol. Enzymic analysis of both the mutant and the parental strain showed that at least three different glycerol dehydrogenases were formed under different physiological conditions: the NAD(+)-dependent enzyme described above, a constitutive NADP(+)-dependent enzyme and a D-glyceraldehyde-specific enzyme induced on D-galacturonate. The glycerol kinase mutant showed impaired growth on D-galacturonate.

The development of a heterologous transformation system for the cellulolytic fungus Trichoderma reesei based on a pyrG-negative mutant strain

Six uridine auxotroph mutants of Trichoderma reesei QM 9414 were isolated by resistance to 5-fluoroorotic acid and one strain was identified as OMP-decarboxylase negative (pyr-) by a radiometric enzyme assay. Transformation to uridine prototrophy was achieved with the pyr4 gene of Neurospora crassa (up to 1500 transformants/micrograms) and with pyrA of Aspergillus niger (700-800 transformants/micrograms). In many transformants the PYR+ function seems to be present as extrachromosomal DNA. There is evidence for a correlation between the stability of transformants and integration of the vector in the genome whereas unstable transformants are obtained when autonomous replication of the plasmid occurs.

Screening method for large numbers of dye-adsorbents for enzyme purification

A method is described by means of which 96 different dye-adsorbents can be tested simultaneously for their ability to bind enzymes and to test their biospecific elution. Small amounts of cell-free extract are applied to dye-adsorbents which are packed in a 96-well transplate cartridge. After biospecific elution, the amount of the eluted enzyme is tested in a microtitre plate assay. The method is illustrated by the purification of glycerol dehydrogenase (E.C. 1.1.1.72), 6-phosphogluconate dehydrogenase (E.C. 1.1.1.44) and glucose-6-phosphate dehydrogenase (E.C. 1.1.1.49) from the hyphal fungus Aspergillus nidulans.

Purification and properties of NADP(+)-dependent glycerol dehydrogenases from Aspergillus nidulans and A. niger

Glycerol dehydrogenase, NADP(+)-specific (EC 1.1.1.72), was purified from mycelium of Aspergillus nidulans and Aspergillus niger using different purification procedures. Both enzymes had an Mr of approximately 38,000 and were immunologically cross-reactive, but had different amino acid compositions and isoelectric points. For both enzymes, the substrate specificity was limited to glycerol and erythritol for the oxidative reaction and to dihydroxyacetone (DHA), diacetyl, methylglyoxal, erythrose and D-glyceraldehyde for the reductive reaction. The A. nidulans enzyme had a turnover number twice that of the A. niger enzyme at pH 6.0, whereas inhibition by NADP+ was less (Ki = 45 microM vs 13 microM). It is proposed that both enzymes catalyse in vivo the reduction of DHA to glycerol and that they are regulated by the anabolic reduction charge.

Isolation and structure of the pectin lyase D-encoding gene from Aspergillus niger

The filamentous fungus, Aspergillus niger, produces a number of extracellular pectin-degrading enzymes. We present here the isolation and the complete nucleotide sequence of the gene, pelD, coding for a pectin lyase D (PLD), which was previously described as pectin lyase I (Van Houdenhoven, Ph.D. Thesis, Wageningen, 1975). The deduced amino acid (aa) sequence corresponds to 373 aa residues including a signal peptide of 19 aa. The coding region is interrupted by four short introns (57-65 bp). The nucleotide sequence of the 5'- and 3'-flanking regions is also presented and shows no unusual features. By comparing the deduced aa sequences of the A. niger PLD and a number of bacterial pectate lyases, short regions of homology were found despite the different substrate specificities (high methoxyl-pectin versus low methoxyl-pectin or polygalacturonate) of these enzymes.

Purification and characterization of polygalacturonases produced by the hyphal fungus Aspergillus niger

Five endo-polygalacturonases (poly(1,4-alpha-D-galacturonide) glycanohydrolase, EC 3.2.1.15) and one exo-polygalacturonase (poly(1,4-alpha-D-galacturonide) galacturonohydrolase, EC 3.2.1.67) were isolated from a commercial pectinase preparation derived from Aspergillus niger. All five endo-enzymes could be purified to homogeneity by affinity chromatography on cross-linked alginate, ion-exchange chromatography, chromatofocusing, and gel permeation chromatography. The exo-polygalacturonase was only partially purified but free from endo-polygalacturonase activity. The two most abundant endo-polygalacturonases (endo-I and endo-II), with molecular masses of 55 and 38 kDa, respectively, are quite different with respect to their isoelectric point, specific activity, mode of action on oligomeric substrates, and amino acid composition. The physicochemical properties of the other three endo-polygalacturonases (endo-IIIA, endo-IIIB, and endo-IV), present in low amounts, are quite similar to those of the endo-I type. The pH optima of all these endo-polygalacturonases are in the range of 4.3-4.9.

The influence of pH on rectal absorption of sodium benzoate studied in man by rectal lumen perfusion

The influence of pH on rectal absorption of sodium benzoate in man was studied by means of a rectal lumen perfusion method and compared with in vitro measurements on diffusional transport of sodium benzoate across an octanol/water interface. For nonbuffered solutions of benzoate in vitro, it was shown that mass flux across an octanol/water interface occurs in agreement with the pH-partition model. In vivo however, mass flux increases less with decreasing pH of unbuffered perfusate than is anticipated on the basis of the pH-partition model. Probably an alkaline flow across the rectal mucosa into the lumen is present as a physiological neutralization mechanism. In contrast, buffered solutions of benzoate show a linear relationship between mass flux and decreasing pH in vitro as well as in vivo. The effect of buffer on the concentration profile of benzoic acid is qualitatively explained. It is shown that an alkaline flow across the rectal mucosa only slightly influences absorption of benzoic acid from strongly buffered solutions in the rectal lumen. It is concluded that the use of strong buffers in rectal solutions induces a drastic effect on the pH of the boundary layer, an effect not seen for unbuffered solutions. This phenomenon does not invalidate the pH-partition hypothesis but can be explained by it.

Rhizosphere Acidification by Iron Deficient Bean Plants: The Role of Trace Amounts of Divalent Metal Ions: A Study on Roots of Intact Plants with the Use of C- and P-NMR

Rhizosphere acidification by Fe-deficient bean (Phaseolus vulgaris L.) plants was induced by trace amounts of divalent metal ions (Zn, Mn). The induction of this Fe-efficiency reaction was studied by (14)CO(2) and (11)CO(2) fixation experiments, and with (31)P-NMR on roots of whole plants. The starting and ending of an acidification cycle was closely coupled to parallel changes in CO(2) fixation, within the maximal resolution capacity of 20 min. (31)P-NMR experiments on intact root systems showed one peak which was ascribed to vacuolar free phosphate. At the onset of proton extrusion this peak shifted, indicating increase of pH in the cells. Proton extrusion was inhibited, with a lag period of 2 hours, by the protein synthesis inhibitors cycloheximide and hygromycin. It is assumed that Zn and Mn induce proton extrusion in Fe-deficient bean roots by activating the synthesis of a short-living polypeptide; the NMR data suggest a role for this peptide in the functioning of a proton pumping ATPase in the plasma membrane.

A study on the buffering activity of the human rectum. In vivo demonstration of HCO3- and H+ secretion after rectal application of fluids with an unphysiological pH

The buffering activity of the human rectum was evaluated in various pilot studies, using a rectal lumen perfusion method. Quantitative alkaline and acid secretion was measured, respectively, by direct titration according to the pH-stat method. The change in composition of the perfusate with regard to the test drug benzoate and the concentration HCO3- was detected. The pilot studies suggest that rectal mucosa is capable of neutralizing a pH deviating from the physiological value within a remarkably short time. In the acid region, at least a part of the alkalizing activity is the result of HCO3- secretion. It has been shown that this process is stimulated by the H+ as well as Cl- ions. In the basic region neutralization very likely occurs by means of H+ secretion.

Structure of the Aspergillus nidulans pyruvate kinase gene

The complete nucleotide sequence of the Aspergillus nidulans pyruvate kinase gene, including its flanking sequences, is presented. The gene has a 1,578 bp coding sequence that encodes a protein of 526 amino acids; the latter is strongly homologous to the pyruvate kinases found in Saccharomyces cerevisiae (66%) and mammals (53%). The gene is interrupted by seven introns, three of which are in a conserved position compared to those present in the mammalian pyruvate kinase genes sequenced thus far. A fourth intron within the mononucleotide binding fold domain is in a conserved position with respect to the position of an intron within the NAD+ binding region of maize ADH I. The transcription start site has been determined; a major site of transcription was found 80 bp before the translation initiation codon. The promoter region of the A. nidulans pyruvate kinase gene contains no direct homologies with the TATA or CCAAT sequences in the expected region (30-70 bp) before the transcription initiation site. However, extended CT-enriched regions are found in the promotor region, similar to what has been observed in genes that are highly expressed in Saccharomyces cerevisiae and filamentous fungi.

A rapid purification procedure for pyruvate kinase from the hyphal fungus Aspergillus nidulans

Pyruvate kinase was purified from the filamentous fungus Aspergillus nidulans with a 45-55% yield. The procedure involved dye-affinity chromatography and fast protein liquid chromatography, resulting in highly active and pure enzyme in milligram quantities within 2 days. The purified enzyme, a tetramer with a subunit molecular weight of 65,000 and an isoelectric point of 4.7, was used to determine the amino acid composition.

Isolation and transformation of the pyruvate kinase gene of Aspergillus nidulans

The Aspergillus nidulans pyruvate kinase gene was isolated by heterologous hybridization using the corresponding yeast gene as a probe. A 2.9 kb EcoRI/BamHI fragment, which exclusively hybridized to the yeast gene, was subcloned in pBR322. This clone was used to transform an A. nidulans pkiA deletion mutant to PKI+. The analysis of transformants with respect to the kind of integration revealed about 80% homologous integration--55% by a double cross-over event (type III integration), 25% by a single cross-over event (type I integration). Type II transformants (20%) that arise by non-homologous integration have not been further characterized with respect to the sites of integration. A direct correlation between the number of copies of the gene integrated into the genome and the measured pyruvate kinase activity was found after growth ona glycolytic carbon source. From this, it was concluded that the 2.9 kb EcoRI/BamHI fragment contains the complete pyruvate kinase structural gene, including the promoter region. However, after growth on a gluconeogenic carbon source, the regulation of gene expression was found to be disturbed. On acetate an increase in activity per gene copy (0.2 IU) was found in the transformants, as compared with wild-type levels. It is suggested that the pyruvate kinase gene is regulated by negative control, and that some sequences involved in this regulation are missing in the cloned fragment.