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A L Demain

Publications and source records attributed to A L Demain.

At least 109 records · Page 6Linked to original sources
PubMed1985

Germination-initiated spores of Bacillus brevis Nagano retain their resistance properties.

Initiated spores and vegetative cells of the gramicidin S-producing Bacillus brevis Nagano were compared with respect to their resistance to various forms of stress (osmotic shock-starvation, exposure to ethanol, sonic oscillation, and heat). The resistance of initiated spores to all of these stress situations was considerably greater than that of vegetative cells and approached that of dormant spores. The period during which the initiated spores remained resistant to heat was extended by addition of gramicidin S. The antibiotic may therefore be of survival value to the species in nature by slowing down the development of initiated spores in the outgrowth phase of germination, thereby extending the period during which the cells are resistant to environmental stress.

Bacillus↗
PubMed1985

Ammonium repression of cephalosporin production by Streptomyces clavuligerus.

Production of beta-lactam antibiotics took place during growth of Streptomyces clavulgerus in chemically defined medium. The specific activities of isopenicillin N synthetase ("cyclase"), isopenicillin N epimerase, and deacetoxycephalosporin C synthetase ("expandase") increased during the exponential phase of growth. Specific cephalosporin productivity during fermentation followed a similar pattern, reaching a maximum near the end of the growth phase and decaying rapidly in the stationary phase. Ammonium chloride depressed cephalosporin production, presumably as a result of repression of cyclase and expandase formation, but not of epimerase. No inhibitory effects on enzyme activity by ammonium were found. Addition of tribasic magnesium phosphate [Mg3(PO4)2 X 8H2O] prevented the repression of cyclase and markedly stimulated cephalosporin production. Cephamycin C and, in smaller amounts, O-carbamoyldeacetylcephalosporin C were the only cephalosporins detected. Growth with ammonium resulted in lower titers of both compounds, and did not change the relative proportion of each. The correlation found between cephalosporin productivity and cyclase specific activity in different media suggests that formation of this enzyme may be the rate-limiting step in the pathway.

Amino Acid Isomerases↗
PubMed1985

Effect of side-chain substitution of a CH2 group by sulfur on the antimicrobial activity of natural penicillins and cephalosporins.

The S-carboxymethyl-D-cysteine side-chain analogs of cephalosporin C and deacetoxycephalosporin C were found to have markedly increased in vitro activity against Gram-positive and Gram-negative bacteria compared to the natural antibiotics. The S-carboxymethyl-L-cysteine analogs were less active than the S-carboxymethyl-D-cysteine analogs but against most organisms tested, still more active than the natural compounds. The effect of replacement of CH2 with S was less dramatic in the case of penicillin N and isopenicillin N. The S-carboxymethyl-D-cysteine analog of deacetoxycephalosporin C was found to be orally available in rats.

Administration, Oral↗
PubMed1984

Enzymatic approach to syntheses of unnatural beta-lactams.

Four enzymes associated with the transformation of the peptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) into the beta-lactam antibiotic desacetylcephalosporin C have been isolated from the prokaryotic organism Streptomyces clavuligerus and immobilized. Appropriate choice of the cofactors allows continuous and quantitative conversion of the peptide into either penicillins or cephalosporins at room temperature. The overall process includes four oxidations, two ring closures, and one epimerization. In contrast, cell-free transformations with the eukaryotic organism Cephalosporium acremonium do not proceed beyond the oxidation level of penicillin. The amino acids of the natural peptide ACV can be altered by chemical means; several of the resulting peptides are converted into novel antibiotics by the enzymes of Streptomyces clavuligerus.

Anti-Bacterial Agents↗
PubMed1984

A pure enzyme catalyzing penicillin biosynthesis.

Isopenicillin N synthetase (cyclase) has been purified to homogeneity from Cephalosporium acremonium strain C-10. The enzyme has a molecular weight of 40,000 to 42,000 and yields a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The enzyme was purified in 10 percent yield by a combination of protamine sulfate and ammonium sulfate precipitations, gel filtration, and ion-exchange high-performance liquid chromatography. The purified enzyme can be stabilized with sucrose and stored at -20 degrees C for several weeks without any loss in activity.

Acremonium↗
PubMed1984

Dependence of betaine stimulation of vitamin b(12) overproduction on protein synthesis.

The betaine-stimulated differential synthesis of vitamin B(12), i.e., the increase in B(12) per increase in dry cell weight, by Pseudomonas denitrificans was inhibited by rifampin and chloramphenicol but not by benzylpenicillin and carbenicillin at concentrations of antibiotic that inhibit growth. The level of the first enzyme of corrin (and porphyrin) biosynthesis, delta-aminolevulinic acid synthetase, was decreased to a much greater degree by rifampin and chloramphenicol than by the penicillins. These data support the concept that betaine stimulation of B(12) synthesis is a result of its stimulation of synthesis of delta-aminolevulinic acid synthetase, a labile and presumably rate-limiting enzyme of corrin formation requiring continuous induction. In further support of this hypothesis, it was found that chloramphenicol immediately interfered with both vitamin B(12) and delta-aminolevulinic acid synthetase formation, no matter when it was added to the system.

Journal Article↗
PubMed1984

Enzymatic conversion of the unnatural tripeptide delta-(D-alpha-aminoadipyl)-L-cysteinyl-D-valine to beta-lactam antibiotics.

Incubation of the unnatural tripeptide delta-(D-alpha-aminoadipyl)-L-cysteinyl-D-valine (DLD-ACV) with a partially purified extract of Cephalosporium acremonium resulted in the production of deacetoxycephalosporin C. The extract contained isopenicillin N synthetase (cyclase) and deacetoxycephalosporin C synthetase (expandase) but no penicillin epimerase activity, and was incubated aerobically in the presence of the components of the cyclase and expandase reaction mixtures (Fe++, ascorbate, dithiothreitol, alpha-ketoglutarate and ATP). The reaction was sensitive to penicillinase, indicating penicillin N to be an intermediate. However, when ring expansion was prevented by omission of alpha-ketoglutarate and ATP, no penicillin N was detected.

Acremonium↗
PubMed1984

In vitro biological activities of 6-isosteric penicillins and 7-isosteric cephalosporins.

Antibiotic and penicillinase inhibitor activities of various penicillin and cephalosporin analogs are reported. The compounds include C-6 penicillin and C-7 cephalosporin carbon, oxygen and sulfur analogs obtained by replacing the NH of the amide side chains with CH2, O and S, respectively. In almost all cases, analogs were considerably less active than the standard compounds (benzylpenicillin and cephalothin). However, some of the analogs act as penicillinase inhibitors.

Bacteria↗
PubMed1984

Repression of beta-lactam production in Cephalosporium acremonium by nitrogen sources.

A variety of inorganic and organic nitrogen sources were added to fermentation media to determine their regulatory effects on the production of beta-lactam antibiotics by Cephalosporium acremonium. (NH4)2SO4 at concentrations higher than 100 mM (1.3%) strongly inhibited beta-lactam production. L-Asparagine and L-arginine proved to be the best nitrogen sources tested for beta-lactam production. The optimum concentration of asparagine was 1.2%. Higher concentrations led to NH3 accumulation, increase in pH, and lower growth rates. Addition of tribasic magnesium phosphate [Mg3(PO4)2 X 8H2O] to the (NH4)2SO4-containing medium stimulated beta-lactam production markedly and ammonium repression of the ring-expansion enzyme was reversed. It appears that the ring-expansion step is a very sensitive part of beta-lactam biosynthesis in C. acremonium with respect to nitrogen source repression. Other enzymes may also be sensitive in view of the fact that nitrogen source derepression not only led to increases in cephalosporin C but, to a lesser extent, penicillin N and total beta-lactam titers.

Acremonium↗
PubMed1983

New applications of microbial products.

Microbial secondary metabolites are now being used for applications other than as antibacterial, antifungal, and antitumor agents. These applications include use against parasites (coccidia, helminths) and insects as well as for animal and plant growth stimulation, immunosuppression, uterocontraction, and other pharmacological activities. Further applications are possible in various areas of pharmacology and agriculture, a development catalyzed by the use of simple enzyme assays for screening prior to testing in intact animals or in the field.

Cloning, Molecular↗
PubMed1983

Sporulation and spore properties of Bacillus brevis and its gramicidin S-negative mutant.

The function(s) of the peptide antibiotic, gramicidin S, in its producer, Bacillus brevis Nagano, was investigated. Particular attention was paid to the possible role of gramicidin S in sporulation and spore properties. Sporulation was similar in both the gramicidin S-producing parental strain and a gramicidin S-negative mutant of this strain. Mature parental and mutant spores were equally resistant to UV irradiation, solvents (reported previously) and heat. Thus, the lack of gramicidin S synthesis impairs none of these properties. Contrary to results reported by others, we also found no difference in heat resistance between spores of B. brevis ATCC 8185 and its linear gramicidin-negative mutant, Ml.

Bacillus↗
PubMed1983

Studies on the ring-cyclization and ring-expansion enzymes of beta-lactam biosynthesis in Cephalosporium acremonium.

Micrococcus luteus was found to be very sensitive to isopenicillin N and was used as assay organism for purification of the enzyme isopenicillin N synthetase, which cyclizes delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine to isopenicillin N. Purification of the enzyme from the crude extract obtained by sonication of mycelia of Cephalosporium acremonium CW-19 was carried out by ammonium sulfate precipitation, desalting with Sephadex G-25, gel filtration on LKB ultrogel AcA44 or ion-exchange chromatography on DEAE-Sepharose. The cyclization enzyme was separated from the ring-expansion enzyme and was purified considerably more than 50-fold by this procedure. Using the purified enzyme, we found that the disulfide bis-delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine required reduction to delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine in order to behave as a substrate. The enzyme activity was stimulated by FeSO4 and ascorbate, but other cofactors, including alpha-ketoglutarate, were inactive. In addition to delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine, the enzyme converted adipyl-L-cysteinyl-D-valine, N-acetyl-delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine, and glycyl-delta-(L-alpha-aminoadipyl)L-cysteinyl-D-valine to penicillins. All of these latter peptides were competitive inhibitors of the cyclization reaction. The Km of the cyclization enzyme is 10 times higher than that of the ring-expansion enzyme, deacetoxycephalosporin C synthetase. The pH and temperature optima of the two enzymes were rather similar. Phosphate inhibited ring expansion, but not cyclization. Both enzymes appear to be soluble enzymes of about 31 000 molecular weight.

Acremonium↗
PubMed1983

A new era of exploitation of microbial metabolites.

In the past history of the pharmaceutical industry, secondary metabolites have been screened almost exclusively for antimicrobial activities. This biased and narrow view has severely limited the potential application of microbial metabolites. Fortunately, this situation is changing and we are now entering into a new era in which microbial metabolites are being applied to diseases heretofore only subjected to synthetic compounds. This new approach is the application of microbial secondary metabolites to diseases that are not caused by other bacteria or fungi. For years, major drugs such as hypotensive and anti-inflammatory agents that are used for non-infectious diseases have been strictly synthetic products. Similarly, major therapeutics for parasitic diseases in animals (for example, coccidiostats and anthelminthics) resulted strictly from screens of chemically synthesized compounds followed by molecular modification. However, today fermentation products such as monensin and lasalocid dominate the coccidiostat market. The avermectins, another group of streptomycete products, have high activity against helminths and arthropods. Indeed, their activity appears to be an order of magnitude greater than previously discovered anthelminthic agents, the vast majority of which are synthetic compounds. Umezawa's group in Japan has isolated many microbial products with important pharmacological activities by screening with simple enzymic assays. There is much interest in a natural inhibitor of intestinal glucosidase, which is produced by an actinomycete of the genus Actinoplanes. The aim is to decrease hyperglycaemia and triacylglycerol synthesis in adipose tissue, liver and the intestinal wall of patients with diabetes, obesity and type IV hyperlipidaemia. Another natural compound of interest is mevinolin, a fungal product which acts as a cholesterol-lowering agent in animals. Mevinolin is produced by Aspergillus terreus. In its hydroxyacid form (mevinolinic acid), mevinolin is a potent competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase from liver. It is clear that, although the microbe has contributed greatly to the benefit of mankind, we have merely scratched the surface of the potential of microbial activity.

Animals↗
PubMed1982

Germination initiation and outgrowth of spores of Bacillus brevis strain Nagano and its gramicidin S-negative mutant.

Bacillus brevis strain Nagano and its gramicidin S-negative mutant, BI-7, were compared with respect to germination of their spores produced in several media. Germination initiation occurred in the presence of nutrient broth or L-alanine but not with inosine, glucose, glycerol or fructose; the process was activated by heat. Parental and mutant spores behaved similarly in these experiments. During outgrowth, parental spores remained in this phase of germination much longer than did mutant spores, but only when the parental spores had been harvested from a sporulation medium where significant gramicidin S synthesis had occurred. When parental spores were extracted or treated with an enzyme that hydrolyzes gramicidin S, rapid outgrowth occurred. Adding exogenous gramicidin S or the extract from parental spores to mutant spores lengthened the outgrowth in a dose-dependent manner. The uptake of labeled L-alanine by parental spores was delayed compared to mutant spores in the presence or absence of chloramphenicol. These data suggest a mechanism of action for gramicidin S whereby it interferes in membrane function, such as transport or energy metabolism, in outgrowing spores.

Alanine↗
PubMed1982

Saccharification of Complex Cellulosic Substrates by the Cellulase System from Clostridium thermocellum.

True cellulase activity has been demonstrated in cell-free preparations from the thermophilic anaerobe Clostridium thermocellum. Such activity depends upon the presence of Ca and a thiol-reducing agent of which dithiothreitol is the most promising. Under these conditions, native (cotton) and derived forms of cellulose (Avicel and filter paper) were all extensively solubilized at rates comparable with cellulase from Trichoderma reesei. Maximum activity of the Clostridium cellulase was displayed at 70 degrees C and at pH 5.7 and 6.1 on Avicel and carboxymethylcellulose, respectively. In the absence of substrate at temperatures up to 70 degrees C, carboxymethylcellulase was much more unstable than the Avicel-hydrolyzing activity.

Journal Article↗