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R L Weiss

Publications and source records attributed to R L Weiss.

At least 91 records · Page 5Linked to original sources
PubMed1982

Energy requirement for the mobilization of vacuolar arginine in Neurospora crassa.

The bulk of the intracellular arginine pool in exponentially growing mycelia of Neurospora crassa is sequestered in the vacuoles. Vacuolar arginine effluxes from the vacuoles into the cytosol and is catabolized to ornithine and urea upon nitrogen starvation. The energy requirement for mobilization has been studied by treating nitrogen-starved mycelia with inhibitors or respiration or glycolysis or an uncoupler of respiration. Mobilization was inhibited by the inhibitors or the uncoupler of respiration, but not by the inhibitors of glycolysis. The inhibitors and the uncoupler of respiration reduced the ATP pool and the energy charge of the treated mycelia. The inhibitors of glycolysis reduced the ATP pool but had no effect on the energy charge. The results indicate that mobilization of arginine from the vacuoles requires metabolic energy. The forms of this energy and the mode of its association with the mobilization process are discussed.

Adenine Nucleotides↗
PubMed1981

15N NMR studies of nitrogen metabolism in intact mycelia of Neurospora crassa.

Suspensions of intact mycelia of Neurospora crassa grown in medium containing 15NH4Cl have been found to give well-resolved 15N nuclear magnetic resonance spectra for metabolites that play crucial roles in intermediary nitrogen metabolism. These include the amide nitrogen of glutamine, the alpha-amino nitrogens of glutamate and other amino acids, the guanidino nitrogens of arginine, the ureido nitrogen of citrulline, the side-chain nitrogens of ornithine or lysine, or both, and uridine diphosphates. The turnover time of glutamine in vivo was estimated to be less than 1 hr by using nuclear magnetic resonance spectroscopy in conjunction with tracer methodologies. Applications of these techniques to the study of nitrogen metabolism are discussed.

Amino Acids↗
PubMed1980

Acetylglutamate kinase. A mitochondrial feedback-sensitive enzyme of arginine biosynthesis in Neurospora crassa.

The radioisotopic method used to assay acetylglutamate kinase (EC 2.7.2.8) of Neurospora crassa has been shown to detect two distinct enzymatically catalyzed reactions. The enzymes were separated by differential centrifugation into a cytosolic activity and an organellar activity. Both activities required ATP and were thermal-labile. The cytosolic activity was insensitive to inhibition by arginine and formed a stable reaction product in the absence of hydroxylamine. The organellar activity had an absolute requirement for hydroxylamine in order to form a stable reaction product. The product of the cytosolic activity was separated from acetylglutamate hydroxamate (the product of the organellar activity) and was identified as the cyclic amide pyroglutamate by cation exchange chromatography. The organellar activity has been implicated in arginine biosynthesis by the following criteria: it was completely and specifically inhibited by arginine concentrations as low as 200 microM; its level was elevated 2-fold in a mutant strain with derepressed levels of arginine biosynthetic enzymes; and it was absent in an arginine auxotrophic strain (the cytosolic activity was present). The organellar activity co-sedimented with mitochondria during isopycnic gradient centrifugation. The metabolic problems posed by a mitochondrial location of a feedback-sensitive enzyme and the cytosolic location of its effector are discussed.

Arginine↗
PubMed1980

Effect of carbon source on enzymes and metabolites of arginine metabolism in Neurospora.

The levels of enzymes and metabolites of arginine metabolism were determined in exponential cultures of Neurospora crassa grown on various carbon sources. The carbon sources decreased in effectiveness (as determined by generation times) in the following order: sucrose, acetate, glycerol, and ethanol. The basal and induced levels of the catabolic enzymes, arginase (EC 3.5.3.1) and ornithine transaminase (EC 2.6.1.13), were lower in mycelia grown on poor carbon sources. Arginase was more sensitive to variations in carbon source than was ornithine transaminase. Induction of both enzymes was sensitive to nitrogen metabolite control, but this sensitivity was reduced in mycelia grown on glycerol or ethanol. The pools of arginine and ornithine were reduced in mycelia grown in unsupplemented medium containing poor carbon sources, but the biosynthetic enzyme ornithine transcarbamylase (EC 2.1.3.3) was not derepressed. The arginine pools were similar, regardless of carbon source, in mycelia grown in arginine-supplemented medium. The ornithine pool was reduced by growth on poor carbon sources. The rate of arginine degradation was proportional to the level of arginase in both sucrose- and glycerol-grown mycelia. The distribution of arginine between cytosol and vesicles was only slightly altered by growth on glycerol instead of sucrose. The slightly smaller cytosolic arginine concentration did not appear to be sufficient to account for the alterations in basal and induced enzyme levels. The results suggest a possible carbon metabolite effect on the expression or turnover of a variety of genes for enzymes of arginine metabolism in Neurospora.

Acetates↗
PubMed1980

Control of arginine metabolism in Neurospora: flux through the biosynthetic pathway.

The flux into the arginine biosynthetic pathway of Neurospora crassa was investigated using a mutant strain lacking the ornithine-degrading enzyme ornithine aminotransferase (EC 2.6.1.13). Flux was measured by the increase in the sum of the radioactivity (derived from [14C]glutamic acid) in the ornithine pool, the arginine pool, and arginine incorporated into proteins. Complete cessation of flux occurred immediately upon the addition of arginine to the growth medium. This response occurred prior to expansion of the arginine pool. After short-term exposure to arginine (80 min), flux resumed quickly upon exhaustion of arginine from the medium. This took place despite the presence of an expanded arginine pool. Initiation of flux required approximately 80 min when the mycelia were grown in arginine-supplemented medium for several generations before exhaustion of the exogenous arginine. The arginine pool of such mycelia was similar to that found in mycelia exposed to exogenous arginine for only 80 min. The results are consistent with rapid onset and release of feedback inhibiton of arginine biosynthesis in response to brief exposure to exogenous arginine. The insensitivity of flux to the size of the arginine pool is consistent with a role for compartmentation in this regulatory process. The lag in initiation of flux after long-term growth in the presence of exogenous arginine suggests the existence of an additional regulatory mechanism(s). Several possibilities are discussed.

Arginine↗
PubMed1980

Isolation and characterization of Neurospora crassa mutants impaired in feedback control of ornithine synthesis.

Thirty-two independent mutants were isolated which overcame the proline requirement of pro-3 mutations in Neurospora crassa. The mutations were not revertants, appeared to be allelic, were closely linked or allelic to arg-6, and in strains unable to degrade ornithine no longer suppressed the proline requirement. The suppressor mutations did not alter the levels of biosynthetic or catabolic enzymes, yet allowed accumulation of ornithine. Suppressed strains unable to degrade arginine still produced ornithine (as detected by growth) in arginine-supplemented medium. The results suggest that the suppressor mutants were impaired in the feedback inhibition of ornithine synthesis by arginine. The activity of the appropriate biosynthetic enzyme was less sensitive to inhibition by arginine. The potential usefulness of such mutations is discussed.

Arginine↗
PubMed1980

Scanning electron microscope autoradiography of critical point dried biological samples.

A technique has been developed for the localization of isotopes in the scanning electron microscope. Autoradiographic studies have been performed using a model system and a unicellular biflagellate alga. One requirement of this technique is that all manipulations be carried out on samples that are maintained in a liquid state. Observations of a source of radiation (125I-ferritin) show that the nuclear emulsion used to detect radiation is active under these conditions. Efficiency measurement performed using 125I-ferritin indicate that 125-I-SEM autoradiography is an efficient process that exhibits a 'dose dependent' response. Two types of labeling methods were used with cells, surface labeling with 125I and internal labeling with 3H. Silver grains appeared on labeled cells after autoradiography, removal of residual gelatin and critical point drying. The location of grains was examined on a flagellated green alga (Chlamydomonas reinhardi) capable of undergoing cell fusion. Fusion experiments using labeled and unlabeled cells indicate that 1. Labeling is specific for incorporated radioactivity; 2. Cell surface structure is preserved in SEM autoradiographs and 3. The technique appears to produce reliable autoradiographs. Thus scanning electron microscope autoradiography should provide a new and useful experimental approach.

Autoradiography↗
PubMed1979

Mobilization of sequestered metabolities into degradative reactions by nutritional stress in Neurospora.

The pools of arginine and ornithine rapidly disappear during nitrogen starvation of Neurospora crassa. Much of this disappearance can be accounted for by degradation catalyzed by preexisting catabolic enzymes. Purine degradation is also initiated by nitrogen metabolic stress. Mobilization of these compounds into degradative reactions does not appear to be a general response to nutritional stress since neither carbon starvation nor inhibition of protein synthesis elicits this response. It is suggested that nitrogen starvation may specifically alter the distribution of arginine and ornithine between vesicles and cytosol. This would be sufficient to initiate and maintain their degradation. These result suggest that compartmentation of amino acids provides a metabolic reserve to be utilized during periods of specific nutritional stress.

Arginase↗
PubMed1978

Mycoplasma capping on lymphocytes.

When mycoplasmas infect lymphocytes they behave as multivalent ligands and cap on the lymphoid cell surface in the absence of added specific antibody. There is an apparent high correlation between mycoplasma capping and blast transormation of the infected lymphocytes. Mycoplasma caps are shed from the surface of cells as an aggregate containing host membrane vesicles. This novel interaction may suggest a physiological role for the phenomenon of capping and may play a part in mycoplasma pathogenesis.

Animals↗
PubMed1978

Intracellular compartmentation and transport of metabolites.

The intracellular locations of enzymes and metabolites were determined for ornithine metabolism in Neurospora. Pulse label experiments were used to measure the rates of intracellular translocations and the sizes of compartmented pools of metabolites in the mitochondrial, cytosolic and vesicular compartments. The results indicate that rapid equilibration occurs between these pools during growth in minimal medium, although the vast majority of the ornithine is confined to the vesicular compartment. Arginine, the biosynthetic end-product of ornithine metabolism, regulates ornithine utilization through a combination of feedback inhibition, repression, and control of intracellular translocations. The last phenomenon plays a decisive role indicating that the regulation of intercompartmental translocations may be a common mechanism in rapid adaptation responses in eukaryotic cells.

Arginine↗
PubMed1978

Interrelationships between microtubules, a striated fiber, and the gametic mating structure of Chlamydomonas reinhardi.

The microtubule system associated with the Chlamydomonas reinhardi flagellar apparatus is shown to differ from previous descriptions; two of the four flagellar "roots" possess only two microtubules and are associated with a finely striated fiber. In gametic cells this fiber underlies the gametic mating structure and makes contact with it. Functional interpretations are offered.

Animals↗
PubMed1978

Behavioral marriage therapy. III. The contents of Gurman et al. may be hazardous to our health.

This paper was written as a reply to a critique of behavioral marital therapy (BMT) by Gurman, Kniskern, and Knudson (6, 7). The reply is divided into four sections. First, the paper addresses the critics' comments on the conceptual model put forth by BMT, correcting and clarifying various misconceptions, and restating some of the basic ideological principles in the behavioral model. Second, the paper discusses behavioral change techniques and technology, along with extratechnological treatment considerations. Again, misrepresentations of BMT are corrected. Third, an analysis of the literature investigating the therapeutic efficacy of BMT is reviewed, and the conclusion is reached that BMT is demonstrably effective, at least for a substantial number of mildly to moderately distressed couples. Criticisms are made of the analysis of the same literature conducted by Gurman et al. We conclude that, contrary to the spirit of the paper by Gurman et al., BMT is a viable framework for conceptualizing and treating relationship problems and that the commitment of its adherents to experimental investigation promises continued evolution, refinement, and improvement.

Behavior Therapy↗