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Biomedical subjects

N H Horowitz

Publications and source records attributed to N H Horowitz.

At least 19 recordsLinked to original sources
PubMed1981

Cellular and extracellular siderophores of Aspergillus nidulans and Penicillium chrysogenum.

Aspergillus nidulans and Penicillium chrysogenum produce specific cellular siderophores in addition to the well-known siderophores of the culture medium. Since this was found previously in Neurospora crassa, it is probably generally true for filamentous ascomycetes. The cellular siderophore of A. nidulans is ferricrocin; that of P. chrysogenum is ferrichrome. A. nidulans also contains triacetylfusigen, a siderophore without apparent biological activity. Conidia of both species lose siderophores at high salt concentrations and become siderophore dependent. This has also been found in N. crassa, where lowering of the water activity has been shown to be the causal factor. We used an assay procedure based on this dependency to reexamine the extracellular siderophores of these species. During rapid mycelial growth, both A. nidulans and P. chrysogenum produced two highly active, unidentified siderophores which were later replaced by a less active or inactive product--coprogen in the case of P. chrysogenum and triacetylfusigen in the case of A. nidulans. N. crassa secreted coprogen only. Fungal siderophore metabolism is varied and complex.

Aspergillus nidulans↗
PubMed1976

Isolation and identification of the conidial germination factor of Neurospora crassa.

The germination-essential substance (germination factor [GF]) that is lost from conidia of Neurospora crassa on exposure to solutions of low water activity has been isolated and identified as a group of iron-transport compounds, or siderochromes. The principal siderochrome of conidia is ferricrocin, a cyclic hexapeptide. A closely related substance, ferrichrome C, is tentatively identified as a minor constituent. The same substances are also present in extracts of mycelium along with small amounts of a third siderochrome, which has not been identified. The GF activity of culture filtrates is due to coprogen, the only siderochrome previously identified with N. crassa.

Chemical Phenomena↗
PubMed1974

Membrane permeability and the loss of germination factor from Neurospora crassa at low water activities.

Neurospora crassa conidia incubating in buffer at low water activities (a(w)) release a germination-essential component as well as 260-nm absorbing and ninhydrin-positive materials, regardless of whether an electrolyte or non-electrolyte is used to reduce a(w). Chloroform and antibiotics known to increase cell-membrane permeability have a similar effect. This suggests that membrane damage occurs in media of low a(w) and that an increase in permeability is responsible for the release of cellular components. The damage caused in media of low a(w) is nonlethal in most cases, and the conidia recover when transferred to nutrient medium.

Cell Membrane Permeability↗
PubMed1971

Germination and growth of neurospora at low water activities.

When the water activity (a(w)) of the medium is lowered by the addition of NaCl or nonelectrolytes, an inhibition of germination, growth rate, and total growth is observed in Neurospora crassa. Inhibition of conidial germination is separable from the other effects and is caused, in large measure, by the loss from conidia in media of low water activity of a substance that is essential for their germination. The substance is detectable in the medium and is also extractable from cultures. It is dialysable and thermostable, and it appears to be highly active. It is not detectable in complete medium.

Journal Article↗
PubMed1971

Photocatalytic Production of Organic Compounds from CO and H(2)O in a Simulated Martian Atmosphere.

[(14)C]CO(2) and [(14)C]organic compounds are formed when a mixture of [(14)C]CO and water vapor diluted in [(12)C]CO(2) or N(2) is irradiated with ultraviolet light in the presence of soil or pulverized vycor substratum. The [(14)C]CO(2) is recoverable from the gas phase, the [(14)C]organic products from the substratum. Three organic products have been tentatively identified as formaldehyde, acetaldehyde, and glycolic acid. The relative yields of [(14)C]CO(2) and [(14)C]organics are wavelength- and surface-dependent. Conversion of CO to CO(2) occurs primarily at wavelengths shorter than 2000 A, apparently involves the photolysis of water, and is inhibited by increasing amounts of vycor substratum. Organic formation occurs over a broad spectral ranger below 3000 A and increases with increasing amounts of substratum. It is suggested that organic synthesis results from adsorption of CO and H(2)O on surfaces, with excitation of one or both molecules occurring at wavelengths longer than those absorbed by the free gases. This process may occur on Mars and may have been important on the primitive earth.

Journal Article↗