Ultraviolet microscopy of purine compounds in the yeast vacuole

Uric acid in plants and microorganisms: Biological applications and genetics - A review

Uric acid increased accumulation and/or reduced excretion in human bodies is closely related to pathogenesis of gout and hyperuricemia. It is highly affected by the high intake of food rich in purine. Uric acid is present in both higher plants and microorganisms with species dependent concentration. Urate-degrading enzymes are found both in plants and microorganisms but the mechanisms by which plant degrade uric acid was found to be different among them. Higher plants produce various metabolites which could inhibit xanthine oxidase and xanthine oxidoreductase, so prohibit the oxidation of hypoxanthine to xanthine then to uric acid in the purine metabolism. However, microorganisms produce group of degrading enzymes uricase, allantoinase, allantoicase and urease, which catalyze the degradation of uric acid to the ammonia. In humans, researchers found that several mutations caused a pseudogenization (silencing) of the uricase gene in ancestral apes which exist as an insoluble crystalloid in peroxisomes. This is in contrast to microorganisms in which uricases are soluble and exist either in cytoplasm or peroxisomes. Moreover, many recombinant uricases with higher activity than the wild type uricases could be induced successfully in many microorganisms. The present review deals with the occurrence of uric acid in plants and other organisms specially microorganisms in addition to the mechanisms by which plant extracts, metabolites and enzymes could reduce uric acid in blood. The genetic and genes encoding for uric acid in plants and microorganisms are also presented.

Yeast Vacuole Inheritance and Dynamics

The vacuole/lysosome of the budding yeast Saccharomyces cerevisiae is actively divided between mother and daughter cells. Vacuole inheritance initiates early in the cell cycle and ends in G2, just prior to nuclear migration. The process begins with a portion of the vacuole extending into the emerging bud. This tubular-vesicular entity, the segregation structure, enables continued exchange of vacuole contents between mother and daughter vacuoles. Genetic, biochemical, and cytological analyses of vacuole inheritance have provided insight into the molecular basis of membrane movement, the spatial and temporal control of organelle transport, and the molecular basis of membrane fusion and fission.

LOCALIZATION OF CYTOPLASMIC NUCLEIC ACID DURING GROWTH AND ENCYSTMENT OF ENTAMOEBA INVADENS

With a modified color-translating ultraviolet microscope, the distribution of material showing an absorption maximum at 265 mµ was studied in samples from whole cultures of Entamoeba invadens at intervals during growth and from cysts allowed to mature under controlled conditions. Absorption by the cytoplasm in general gradually increased as trophozoites approached the period of maximum encystment. In late trophozoites and precystic forms, the absorbing material was concentrated into small bodies which coalesced to form large crystalloids of very high specific absorption. Maximum crystallization occurred in early cysts, where cytochemical tests have shown the large crystalloids to be ribonucleoprotein. Electron micrographs show that the crystalloids are composed of particles 200 to 300 A in diameter. During cyst maturation the amount of absorbing material per cyst is not visibly reduced, but the large bodies fragment into smaller units until finally there is only a very high diffuse absorption over the entire cyst. From these and other results the hypothesis is advanced that the large crystalloids ("chromatoid bodies") are a manifestation of a special parasite-host adaptive mechanism; ribonucleoprotein is synthesized under favorable conditions, crystallized in the resistant cyst stage, and dispersed in the newly excysted amebae thereby enabling them to establish themselves in a new host by a period of quick growth.

ULTRAVIOLET MICROSCOPY OF THE VACUOLE OF SACCHAROMYCES CEREVISIAE DURING SPORULATION

Svihla, G. (Argonne National Laboratory, Argonne, Ill.), J. L. Dainko, and F. Schlenk. Ultraviolet microscopy of the vacuole of Saccharomyces cerevisiae during sporulation. J. Bacteriol. 88:449-456. 1964.-Normal cells of Saccharomyces cerevisiae and cells containing, in their vacuoles, large quantities of S-adenosylmethionine were induced to sporulate. In the latter case, the strong ultraviolet absorption of the compound permitted photomicrographic observation of cytological detail. Chromatographic and spectrophotometric analyses of cell extracts supplemented the cytological studies. The vacuole is abolished at the onset of sporulation, and its contents may be observed temporarily in the intersporular space. As sporulation progresses, the material is discharged into the culture medium. Sporulation of both types of cells also leads to a release of nucleic acid fragments into the culture medium.

Amphotericin B-induced changes in K+ content, viability, and ultrastructure of yeast-phase Histoplasma capsulatum

Yeast-phase cells of Histoplasma capsulatum were challenged with amphotericin B, and membrane perturbation was monitored by K+ efflux. Suspensions of washed cells readily absorbed about 1.12 microgram of amphotericin B per mg (dry weight) and further nonspecific sites were also apparent. The dose-response curve for initial rate of K+ efflux was sigmoidal within the range 0.1 to 1.0 microgram of amphotericin B per ml. A fungistatic concentration of amphotericin B (0.3 microgram/ml) evoked an efflux of 85 to 90% K+ from the cells within 15 min, but cell viability decreased only 13% (yeast phase) or 33% (transformed to mycelial units). Ultrastructural changes in treated cells were detected within 5 min, and the hallmark was expansion of vacuoles during the 1-h monitoring period. In contradistinction to a previous report, the appearance of the protoplasmic membrane was not altered by fungistatic concentration. When treated cells were returned to a fresh growth medium, there was a pronounced lag (20 h). During this apparent recovery phase, the large vacuoles fragmented and returned to normal size. It is proposed that vacuoles of H. capsulatum act as a spatial buffer of considerable survival value to stressed cells.

Studies on purine transport and on purine content in vacuoles isolated from Saccharomyces cerevisiae

The transport of purine derivatives into vacuoles isolated from Saccharomyces cerevisiae was studied. Vacuoles which conserved their ability to take up purine compounds were prepared by a modification of the method of polybase-induced lysis of spheroplasts. Guanosine greater than inosine = hypoxanthine greater than adenosine were taken up with decreasing initial velocities, respectively; adenine was not transported. Guanosine and adenosine transporting systems were saturable, with apparent Km values 0.63 mM and 0.15 mM respectively, while uptake rates of inosine and of hypoxanthine were linear functions of their concentrations. Adenosine transport in vacuoles appeared strongly dependent on the growth phase of the cell culture. The system transporting adenosine was further characterized by its pH dependency optimum of 7.1 and its sensitivity to inhibition by S-adenosyl-L-methionine. In the absence of adenosine in the external medium, [14C]adenosine did not flow out from preloaded vacuoles. However, in the presence of external adenosine, a very rapid efflux of radioactivity was observed, indicating an exchange mechanism for the observed adenosine transport in the vacuoles. In isolated vacuoles the only purine derivative accumulated was found to be S-adenosyl-L-homocysteine.

Metabolite compartmentation in Saccharomyces cerevisiae

Uninduced cultures of Saccharomyces cerevisiae exhibit high basal levels of allantoinase, allantoicase, and ureidoglycolate hydrolase, the enzymes responsible for degrading allantoin to urea. As a result, these activities increase only 4- to 8-fold upon induction, whereas the urea-degrading enzymes, urea carboxylase and allophanate hydrolase, have very low basal levels and routinely increase 30-fold on induction. Differences in the inducibility of these five enzymes were somewhat surprising because they are all part of the same pathway and have the same inducer, allophanate. Our current studies reconcile these observations. S. cerevisiae normally contained up to 1 mM allantoin sequestered in a cellular organelle, most likely the vacuole. Separation of the large amounts of allantoin and the enzymes that degrade it provide the cell with an efficient nitrogen reserve. On starvation, sequestered allantoin likely becomes accessible to these degradative enzymes. Because they are already present at high levels, the fact that their inducer is considerably removed from the input allantoin is of little consequence. This suggests that at times metabolite compartmentation may play an equal role with enzyme induction in the regulation of allantoin metabolism. Metabolism of arginine, another sequestered metabolite, must be controlled both by induction of arginase and compartmentation because arginine serves both as a reserve nitrogen source and a precursor of protein synthesis. The latter function precludes the existence of high basal levels of arginase.

Induction and inhibition of the allantoin permease in Saccharomyces cerevisiae

Allantoin uptake in Saccharomyces cerevisiae is mediated by an energy-dependent, low-Km, active transport system. However, there is at present little information concerning its regulation. In view of this, we investigated the control of alloantoin transport and found that it was regulated quite differently from the other pathway components. Preincubation of appropriate mutant cultures with purified allantoate (commercial preparations contain 17% allantoin), urea, or oxalurate did not significantly increase allantoin uptake. Preincubation with allantoin, however, resulted in a 10- to 15-fold increase in the rate of allantoin accumulation. Two allantoin analogs were also found to elicit dramatic increases in allantoin uptake. Hydantoin and hydantoin acetic acid were able to induce allantoin transport to 63 and 95% of the levels observed with allantoin. Neither of these compounds was able to serve as a sole nitrogen source for S. cerevisiae, and they may be non-metabolizable inducers of the allantoin permease. The rna1 gene product appeared to be required for allantoin permease induction, suggesting that control was exerted at the level of gene expression. In addition, we have shown that allantoin uptake is not unidirectional; efflux merely occurs at a very low rate. Allantoin uptake is also transinhibited by addition of certain amino acids to the culture medium, and several models concerning the operation of such inhibition were discussed.

Characterization of a specific transport system for arginine in isolated yeast vacuoles

The transport of L-arginine was studied in isolated vacuoles of Saccharomyces cerevisiae. A centrifugation method allowed rapid separation of the fragile vacuoles from the incubation media so that initial uptake rates of [14C]arginine could be measured. Labelled arginine added to the medium was accumulated in the isolated vacuoles; it was found to exchange specifically with the arginine already present in the vacuoles. Such an exchange did not take place in intact spheroplasts. The pH dependence of the arginine transport in the vacuoles was tested. As the vacuoles are unstable in the pH range of optimal transport activity (pH above 7.0), the pH optimum of the transport reaction could not be determined. From the temperature dependence, the apparent energy of activation was calculated to be 9800 cal/mol. Arginine transport shows saturation kinetics with an apparent Km of 30 muM in the isolated vacuoles, and of 1.5 muM in the spheroplasts. Competition experiments with amino acids and arginine analogues demonstrated that the arginine transport in both vacuoles and spheroplasts, is highly specific. The two systems, however, were shown to have distinct specificities. The inhibition of vacuolar L-arginine transport by D-arginine, L-histidine, and L-canavanine was competitive with apparent Ki values of 60 muM, 400 muM and 600 muM respectively.

Examination of isolated yeast cell vacuoles for active transport

Isolated vacuoles of the yeast Candida utilis did not show active transport of S-adenosylmethionine, uric acid, and several amino acids which they concentrate in vivo.

Isolation and characterization of the amino-acid pools located within the cytoplasm and vacuoles of Candida utilis

Two distinct amino-acid pools were demonstrated in the food yeast Candida utilis. Treatment of the cells with basic protein (cytochrome c) under isotonic conditions permeabilized the plasmalemma but left the tonoplast intact. The selective effect on these membranes was indicated by the observation of intact vacuoles but changed contrast of the cytoplasm in the phase-contrast microscope and by the free access of a chromogenic substrate to a cytoplasmic enzyme (α-glucosidase). However, only 10-20% of the soluble amino acids were released from the cells and these had a rapid turnover as demonstrated by pulse labelling experiments using (14)C(U)-arginine, (14)C(U)-glucose, and (15)N-ammonia. This indicates a rapidly metabolized amino-acid pool located within the cytoplasm. Osmotic shock with water following the treatment with basic protein disrupted the tonoplast, an event which could be followed by phase-contrast microscopy. Most of the remaining amino acids were then released. These showed a slow turnover in pulse-labelling experiments and a high proportion of basic, nitrogen-rich amino acids, indicative of a storage function. The significance of such vacuolar and cytoplasmic pools in the regulation of cellular metabolism is discussed.

Stability of Candida utilis cells and spheroplasts toward gravitational forces

Candida utilis cells and spheroplasts containing uric acid crystals in their vacuoles were not damaged by the mechanical stress of centrifugation at 20,000 x g for 10 min, as judged by plating, microscopy, and spectrophotometry.

Sai-1 mutation: saccharomyces cerevisiae: characteristics of inhibition by S-adenosylmethonine and S-adenosylhomocysteine and protection by methionine

The relationship of methionine to the inhibition caused by S-adenosylmethionine and S-adenosylhomocysteine in strains containing the sai-1 mutation has been investigated and shown to affect indirectly the survival of the mutants. The ability of the mutants to take up both inhibitors is similar to that of the wild-type cells. The mutant also retains the ability to hydrolyze S-adenosylhomocysteine and incorporate the hydrolytic products into the various cellular fractions. Maximal inhibition of the sai-1 mutants occurs at an extracellular concentration of 0.005 mmS-adenosylmethionine and 0.025 to 0.05 mmS-adenosylhomocysteine when the cellular concentration is 0.05 mg (dry weight) per ml. The results suggest that the sai-1 mutation affects reaction(s) either not associated with methionine biosynthesis, or methionine synthesis and at least one other critical cellular function.

Ultraviolet microscopy of purines and amino acids in the vacuole of Candida albicans

Ultraviolet (UV) microscopy was used to study the capacity of yeast (ATCC 10231 and 10261) and filamentous (ATCC 10259) strains of Candida albicans to accumulate UV-absorbing materials from a medium supplemented with purines, pyrimidines, amino acids, or related compounds as the main nitrogen source. All strains accumulated UV-absorbing compounds when adenine, adenosine, isoguanine, xanthine, or uric acid was supplied as a nitrogen source, but they did not accumulate UV-absorbing compounds when pyrimidines were supplied. The filamentous strain accumulated UV-absorbing material from medium supplemented with hypoxanthine, but the yeast strains did not. In contrast, the yeast strains accumulated more UV-absorbing material than did the filamentous strain when guanine was the nitrogen source. Yeast strain 10231 not only accumulated UV-absorbing material from tyrosine-supplemented medium, but it became filamentous in form as well. Yeast strain 10261 and filamentous strain 10259 did not accumulate detectable amounts of UV-absorbing material, nor was their morphology noticeably affected by the supplement. The two yeast strains accumulated more lipid than the filamentous strain when they were incubated in a nitrogen-deficient medium.

Vacuoles of fungal protoplasts

Details are given of the conditions which allow vacuolar structures of Fusarium culmorum to be released after osmotic bursting of mycelial protoplasts. Steps in the release of vacuoles are shown. The composition of the suspending medium affects the formation, size, and number of the vacuoles seen in the protoplasts. Fusion of vacuoles in regenerating protoplasts has been observed, indicating a self-sealing property of the tonoplast. Preparations of vacuolar structures, rather free from cytoplasmic debris, have been obtained.

Ultraviolet microscopy of Candida albicans

Balish, Edward (Argonne National Laboratory, Argonne, Ill.), and George Svihla. Ultraviolet microscopy of Candida albicans. J. Bacteriol. 92:1812-1820. 1966.-Yeast and mycelial strains of Candida albicans were grown in medium supplemented with sulfur amino acids in an effort to determine factors that control the morphology and pathogenicity of the organism. Ultraviolet microscopy revealed a greater concentration of S-adenosylmethionine in the vacuoles of the mycelial phase than in those of yeast phases. Supplementation with amino acids greatly increased the concentration of S-adenosylmethionine in the mycelial phase, and made these cells more sensitive to the lytic action of snail gut enzymes than two yeast phase strains. This indicates a difference in cell wall structure that may be related to the pathogenicity of the mycelial phase.