SEARCH · Search PubMed

Results for “Phycomyces”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

PubMed1988

Altered expression of chitin synthetase activity and biochemical changes in the cell wall in a developmental mutant of Phycomyces.

The Phycomyces developmental mutant S356 elaborates spores which show a much poorer viability and a higher affinity for Calcofluor White than the wild-type spores. Protease-activated extracts of the mutant spores showed higher levels of chitin synthetase activity than the parental strain-derived spores. High levels of enzyme activity in the mutant extracts, but not in the corresponding wild-type extracts, could be detected in the absence of an exogenous protease. The high basal active chitin synthetase is not the result of activation by endogeneous proteases during cell breakage since protease inhibitors did not reduce, but rather increased, the activity levels. The analysis of cell wall composition in the mutant spores revealed significant changes in the proportion of uronic acids and protein but not in chitin. The mutant phenotype is discussed in relation to the developmental stage at which the alterations connected with cell wall metabolism occurred.

Cell Wall↗

PubMed1996

Prt1, an unusual retrotransposon-like sequence in the fungus Phycomyces blakesleeanus.

This work reports the isolation and structural characterization of Prt1, a 4.7 kb retrotransposon-like sequence from the filamentous fungus Phycomyces blakesleeanus. Two open reading frames are found within Prt1. The first shows no similarity with known genes. The second encodes peptide stretches similar to the reverse transcriptase and RNaseH domains of the Ty3/gypsy family of LTR-retrotransposons. Prt1 lacks long terminal repeats, having instead short (54 bp) terminal inverted repeats. No target site duplication has been found. A single copy of Prt1 was detected in the genome of P. blakesleeanus. Adjacent to this sole copy of Prt1, a cluster of various short sequence repeats, both direct and inverted, is found. These sequences, which are reminiscent of defective, non-retroviral transposable elements, are also represented in other regions of the P. blakesleeanus genome.

Amino Acid Sequence↗

PubMed2003

Analysis of phenomena involved in the apical growth of Phycomyces blakesleeanus.

The effects of the Ca(2+)/H(+) exchanger A23187 and the K(+)/H(+) exchanger nigericin, the electrogenic membrane-potential depleters valinomycin and CCCP, and the calcium channel blockers ruthenium red, nifedipine, and nitrendipine on the apical growth of Phycomyces blakesleeanus were analyzed. While all of the compounds inhibited the growth of germlings in liquid medium, the Ca(2+) channel blockers were the least effective. Chitin synthesis in vivo was also sensitive to the inhibitors; here again, the calcium channel blockers were less efficient, and their effect occurred after a lag phase, in contrast to the electroneutral ionophores whose effects were immediate. The ionophores rapidly inhibited protein secretion, and reduced the number of secretory vesicles and chitosomes in the hyphal apex of P. blakesleeanus. The results suggest that not only tip-to-base calcium gradients but also transmembrane ionic gradients and membrane potential have a role in the apical growth of P. blakesleeanus. They are probably involved in the formation, migration, and/or fusion with the plasmalemma of secretory vesicles and chitosomes.

Calcimycin↗

PubMed1996

Lack of protection by carotenes against gamma-radiation damage in Phycomyces.

Carotenes could protect cells from radiation damage by chemically quenching the free radicals and the activated chemical species originated by the exposure. We tested this hypothesis with strains of the zygomycete Phycomyces blakesleeanus that contained different carotenes (phytoene, lycopene, beta-carotene) or different concentrations of beta-carotene. Pairs of strains were cultured together, exposed to a maximum of 73 Gy gamma-radiation from a Co source, and allowed to recover and grow further together on limited resources. Irradiation did not affect the relative abundance of each strain in the resulting spore crop. Thus, carotenes did not protect the fungal cells against gamma-radiation and did not influence their recovery from damage caused by the exposure.

Carotenoids↗

PubMed2002

Tropisms in Phycomyces: sine law for gravitropism, exponential law for photogravitropic equilibrium.

Sporangiophores of Phycomyces blakesleeanus that are gravitropically stimulated by inclining them relative to the earth's gravitational vector obey the sine law for inclination angles between 0 degrees and 150 degrees. The quantitative relation between gravitropism and phototropism was analyzed for sporangiophores that were kept in balance between opposing gravitational and phototropic stimuli. The gravitropism of inclined sporangiophores was compensated with unilateral light impinging at right angles relative to the axis of the sporangiophore. The fluence rate of unilateral blue light (466 nm) that was required to counteract the negative gravitropism increased exponentially with the sine of the inclination angle of the sporangiophore. The establishment of photogravitropic equilibrium during continuous unilateral irradiation is thus determined by two different laws: the well-known sine law for gravitropism and a novel exponential law of phototropism described in this work. Furthermore, the specific form of the exponential relationship depends on the presence of statoliths (vacuolar protein crystals) and on wavelength.

Gravitropism↗

PubMed2002

Helical growth of stage-IVb sporangiophores of Phycomyces blakesleeanus: the relationship between rotation and elongation growth rates.

An understanding of the relationship between the two components of helical growth (rotation rate and elongation rate) is fundamental to understanding the biophysical and molecular mechanism(s) of cell wall extension in algal cells, fungal cells, and plant stems and roots. Helical growth occurs throughout development of the sporangiophores of Phycomyces blakesleeanus. Previous studies within the growth zone of stage-IVb sporangiophores have reported conflicting conclusions. An implicit assumption in the previous studies [E.S. Castle (1937) J Cell Comp Physiol 9:477-489; R. Cohen and M. Delbruck (1958) J Cell Comp Physiol 52:361-388; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] was that the relationship between rotation rate and elongation rate was independent of the magnitude of the elongation rate. In the present study, for stage-IVb sporangiophores growing at a steady rate, it is shown that the ratio of rotation rate and elongation rate decreases as the elongation rate increases. Previously proposed biophysical and molecular mechanisms cannot account for the observed behavior. The previously postulated fibril-reorientation mechanism [J.K.E. Ortega and R.I. Gamow (1974) J Theor Biol 47:317-332; J.K.E. Ortega et al. (1974) Plant Physiol 53:485-490] is modified to accommodate this new finding. Other experiments were conducted to determine how the ratio of rotation rate and elongation rate behaves during a pressure response (a transient decrease in elongation rate produced by a large step-up in turgor pressure using the pressure probe). Results of these experiments indicate that this ratio increases during the pressure response.

Cell Division↗

PubMed2003

Light-induced fluorescence changes in Phycomyces: evidence for blue light-receptor associated flavo-semiquinones.

Light-induced fluorescence changes (LIFCs) were detected in sporangiophores of the blue-light-sensitive fungus Phycomyces blakesleeanus (Burgeff). The LIFCs can be utilized as a spectrophotometric assay for blue-light photoreceptors and for the in vivo characterization of their photochemical primary reactions. Blue-light irradiation of sporangiophores elicited a transient decrease and subsequent regeneration of flavin-like fluorescence emission at 525 nm. The signals recovered in darkness in about 120 min. In contrast to blue light, near-UV (370 nm) caused an increase in the fluorescence emission at 525 nm. Because the LIFCs were altered in a light-insensitive madC mutant with a defective photoreceptor, the fluorescence changes must be associated with early photochemical events of the transduction chain. Action spectra for the fluorescence changes at 525 nm showed major peaks near 470 and 600 nm. Double-pulse experiments involving two consecutive pulses of either blue and near-UV, blue and red, or near-UV and red showed that the responses depended on the sequence in which the different wavelengths were applied. The results indicate a blue-light receptor with intermediates in the near-UV, blue and red spectral regions. We explain the results in the framework of a general model, in which the three redox states of the flavin photoreceptor, the oxidized flavin (Fl), the flavo-semiquinone (FlH*), and the flavo-hydroquinone (FlH2) are each acting as chromophores with their own characteristic photochemical primary reactions. These consist of the photoreduction of the oxidized flavin generating semiquinone, the photoreduction of the semiquinone generating hydroquinone, and the photooxidation of the flavo-hydroquinone regenerating the pool of oxidized flavins. The proposed mechanism represents a photocycle in which two antagonistic photoreceptor forms, Fl and FlH2, determine the pool size of the biological effector molecule, the flavo-semiquinone. The redox changes that are associated with the photocycle are maintained by redox partners, pterins, that function in the near-UV as secondary chromophores.

Benzoquinones↗

PubMed1998

Reception of far-ultraviolet light in Phycomyces: antagonistic interaction with blue and red light.

Phototropism experiments were done with sporangiophores of the fungus Phycomyces blakesleeanus to characterize the interaction between far-UV, blue and red light. Far-UV light elicits negative phototropism (bending away from the light source) while blue light elicits positive phototropism (bending toward the light source). In contrast, red light above 600 nm is phototropically inert. Phototropism was analyzed with light regimens of bilateral or unilateral irradiation with far-UV and blue light. Under bilateral irradiation, in which the two light sources were facing each other, blue light partially inhibited the far-UV-elicited phototropism. A fluence-response curve for this inhibition showed that blue light was maximally effective at fluence rates which exceeded 3 to 57 times that of the far-UV. Tonic red light, which was given from above, abolished to a large extent the antagonistic action of blue light. With a regimen of unilateral irradiation, i.e. when far-UV and blue light were given from the same side, a phototropic balance could be achieved with approximately equal fluence rates of blue and UV light. Above or below this critical balance point the bending was either negative or positive. In this setup the effect of tonic red light was complex. First, it caused an enhancement of the positive or negative bending, and second, it caused at some fluence rates a sign reversal from positive to negative phototropism. The balance point itself was only marginally affected. The data cannot be explained on the basis of a single photoreceptor and support the previous notion of separate far-UV and blue-light receptors. The antagonism between these two receptors probably occurs on the level of a red-light-absorbing receptor intermediate.

Dose-Response Relationship, Radiation↗

PubMed1999

Gravitropism in Phycomyces: a role for sedimenting protein crystals and floating lipid globules.

To elucidate the graviperception of the unicellular fungus, Phycomyces blakesleeanus, sporangiophores were inspected for intracellular structures which relocate with respect to gravity. Two structures, paracrystalline proteins (so-called octahedral crystals) and an aggregate of lipid globules, were identified which showed redistribution upon reorientation of the sporangiophore. Octahedral crystals occur throughout the sporangiophore, including the apical growing zone, and are localized inside vacuoles in which they reside singly or in clusters of up to 40 loosely associated individuals. Upon a 90 degrees reorientation of sporangiophores, crystal clusters sedimented in approximately 50-200 s from the upper to the lower side, corresponding to a speed of 0.5-2 micrometers s-1. Stage-4 sporangiophores (with sporangium) of three mutants which lack the crystals displayed anormal kinetics of gravitropism and substantially reduced bending angles in comparison to sporangiophores of the wild type. While horizontally placed wild-type sporangiophores reached the vertical position after 10-12 h, the crystal-lacking mutants bent maximally 40 degrees-50 degrees upward. In stage-1 sporangiophores a conspicuous aggregate of lipid globules is positioned about 50 micrometers below the apex. The globules floated upwards when the sporangiophore was placed horizontally forming in this way a cap-like aggregate. It is proposed that both the sedimenting protein crystals and the upward-floating globules are involved in gravisensing.

Crystallization↗

PubMed1983

Ornithine decarboxylase in Phycomyces: in vitro and in vivo properties.

The properties of ornithine decarboxylase from Phycomyces blakesleeanus were examined. Enzyme from mycelial cultures was extracted and purified approximately 70-fold. The apparent molecular weight is 96K. The Michaelis constants with respect to ornithine and pyridoxal 5'-phosphate are 90 and 0.37 microM, respectively. Putrescine is a potent competitive inhibitor with a Ki of 75 microM. Exposure of ornithine decarboxylase to sulfhydryl-modifying reagents resulted in a rapid inhibition of activity. In vivo addition of putrescine produced characteristic decreases in cellular ornithine decarboxylase activity. Light stimulation of dark-adapted mycelial cultures also decreased cellular ornithine decarboxylase activity.

Carboxy-Lyases↗

PubMed1988

Purification of geranylgeranyl diphosphate synthase from Phycomyces blakesleanus.

Geranylgeranyl diphosphate synthase has been purified to homogeneity from the carotene-overproducing strain M1 of Phycomyces blakesleanus. Usually two activity peaks with molecular weights of 60,000 and 30,000 eluted on gel exclusion chromatography, suggesting that the enzyme consists of two subunits, with a tendency to dissociate. With homogeneous protein, a single-staining band with molecular weight of 30,000 appeared on sodium dodecyl sulfate gel electrophoresis, confirming a subunit molecular weight of 30,000. Only isopentenyl diphosphate and farnesyl diphosphate were accepted by this enzyme for geranylgeranyl diphosphate formation. The smaller allylic compounds, dimethylallyl and geranyl diphosphate, were utilized at less than 1/20th the rate of farnesyl diphosphate. Michaelis constants of 9 microM for isopentenyl diphosphate and 60 microM for farnesyl diphosphate were found. The isoelectric point is 4.8.

Dimethylallyltranstransferase↗

PubMed1990

A study of the kinetic mechanism followed by glutathione reductase from mycelium of Phycomyces blakesleeanus.

An investigation of the reaction mechanism of glutathione reductase isolated from the mycelium of Phycomyces blakesleeanus NRRL 1555(-) was conducted. The enzyme showed GSSG concentration-dependent substrate inhibition by NADPH and pH-dependent substrate inhibition by GSSG. At pH 7.5, the kinetic data were consistent with a basic scheme corresponding to the branching mechanism, involving a ping-pong with formation of a dead-end F.NADPH complex and an ordered sequential mechanism. Both pathways have in common the step in which NADPH binds to the free oxidized form (E) of the glutathione reductase. At low concentrations of GSSG the ping-pong mechanism prevails, whereas at high concentrations the ordered mechanism appears to dominate. The data were analyzed on the basis of the limiting ping-pong mechanism with F.NADPH complex formation and of the hybrid mechanism, and the kinetic constants of the model were calculated. The data obtained at acidic pH values do not rule out the possibility that the kinetic model may be more complicated than the basic scheme studied.

Glutathione↗

PubMed1975

Some properties of trehalase from Phycomyces blakesleeanus.

Trehalase (alpha, alpha-trehalase glucohydrolase EC 3.2.1.28) from Phycomyces spores occurs in two different forms which are convertible in vivo: a form with low activity found in dormant spores and an active form after breaking the dormancy. Between the two forms no difference in molecular weight and electrophoretic mobility can be detected. The molecular weight is estimated by gel filtration at about 210 000. The relation between substrate concentration and trehalase activity follows the Michaelis-Menten equation (K-m plus or minus 55 mM) in activated spores whereas in dormant spores trehalase shows a different substrate binding, indicating a negative cooperative effect. They differ further in thermostability and in sensitivity to inhibition by ATP. Other nucleosidephosphates have no inhibiting effect. Heating the spores at different temperatures between 38 and 44 degrees C results in a partial breaking of dormancy of the spore population and a corresponding partial activation of trehalase. This suggests a close connection between breaking dormancy and trehalase activation.

Chromatography, Gel↗

PubMed1976

The subcellular distribution of carotenoids in Phycomyces blakesleeanus C115 car-42 mad-107 (--).

1. Subcellular fractions of the C115 car-42 mad-107(--) strain of Phycomyces blakesleeanus, prepared by differential centrifugation, were irreversibly associated with extraneous lipids. Such contamination was avoided by the use of density gradient centrifugation. 2. The two beta-carotene-containing fractions, a particulate fraction and lipid globules, also contained sterol, phospholipid and alkaline p-nitrophenylphosphatase activity. Both fractions revealed close similarities on amino acid analysis.

Amino Acids↗

PubMed1994

The purification of phytoene dehydrogenase from Phycomyces blakesleeanus.

The carotenogenic enzyme phytoene dehydrogenase has been purified from the C9carR21(-) (lycopene-accumulating) mutant of the filamentous fungus Phycomyces blakesleeanus. Solubilization of the membrane-bound enzyme with 1% Tween-60 was followed by a 250-fold purification to homogeneity using polyethylene glycol precipitation, CM-Sepharose, gel filtration and isoelectric focusing. Multiple peaks of enzymic activity were found in eluates from ion-exchange and gel filtration chromatography, with the lowest molecular weight fraction having an apparent molecular mass of approx. 14 kDa. All active fractions catalyzed the dehydrogenation of 15-cis phytoene into all-trans lycopene, with a cis-trans isomerization occurring at phytofluene. Both NADP+ and FAD were required for the dehydrogenation reaction. The presence of > 0.5% Tween-60 was necessary to maintain enzymic activity, although in its absence lipids restored some activity. The enzyme could be stored for at least 6 weeks at -70 degrees C in the presence of 20% (v/v) glycerol.

Chromatography, Gel↗

PubMed1976

Ribosomal RNA synthesis in the mycelium of Phycomyces blakesleeanus. High molecular weight RNA.

Total RNA was extracted from 24 h old mycelia of Phycomyces blakesleeanus which had been grown in liquid culture. Heavy molecular weight RNA was fractionated on 2.6% polyacrylamide gels. 1. The main cytoplasmic ribosomal RNA fractions had molecular weights of 1.34 and 0.72-16(6). 2. [3H]Uridine pulse labelling of cultures revealed an initial ribosomal RNA precursor of molecular weight 2.5-10(6). 3. An intermediate precursor for the 1.34 - 10(6) dalton peak was found, having a molecular weight of 1.6-10(6). 4. Pulse-chase experiments, using [3H]methionine, showed the flow of synthesis as being (see article). 5. Mature 0.72-10(6) dalton RNA appeared prior to the 1.34-10(6) dalton RNA but no immediate precursor for it was detected.

Electrophoresis, Polyacrylamide Gel↗

PubMed1988

12-O-tetradecanoyl phorbol-13-acetate interferes with germination of Phycomyces blakesleeanus sporangiospores.

The presence of protein kinase C (PKC), a key enzyme in signal transduction, has not been investigated in fungal cells. The phorbol ester TPA, an activator of PKC, may be used as an indicator of the presence and role of PKC in Phycomyces blakesleeanus spores. Activation of spore germination by acetate was prevented by 6 nM TPA. The TPA analog 4 alpha PDD, an ineffective activator of PKC, did not affect spore germination. 3 mM dbcAMP, on the other hand, reversed the inhibition of germination caused by TPA. TPA-stimulated protein kinase activity was detected in spores. The possible relationship between PKC and the increased levels of cAMP that accompany the induction of spore germination is discussed.

Bucladesine↗

PubMed1984

The kinetic mechanism of pyruvate reduction by lactate dehydrogenase from Phycomyces blakesleeanus.

The kinetics of pyruvate reduction by lactate dehydrogenase from Phycomyces blakesleeanus NRRL 1555 (-) have been determined at pH 6.0. Initial rate studies performed in the pyruvate reduction direction suggest that a sequential mechanism is operating. Product inhibition studies with NAD+ and L(+)-lactate are consistent with an ordered sequential mechanism if we considered that NAD+ mimics the NADH that binds cooperatively on the enzyme and also the existence of dead-end complex responsible for substrate inhibition by pyruvate at this pH value.

Fungi↗