Ultrastructure of methanol-utilizing yeast cells: appearance of microbodies in relation to high catalase activity

Visualization of yeast cells by electron microscopy

In the 1970s, hydrocarbon or methanol utilizable yeasts were considered as a material for foods and ethanol production. During the course of studies into the physiology of yeasts, we found that these systems provide a suitable model for the biogenesis and ultrastructure research of microbodies (peroxisomes). Microbodies of hydrocarbon utilizing Candida tropicalis multiply profusely from the preexisting microbody. β oxidation enzymes in the microbody were determined by means of immunoelectron microscopy. We examined the ultrastructure of Candida boidinii microbodies grown on methanol, and found a composite crystalloid of two enzymes, alcohol oxidase and catalase, by analyzing using the optical diffraction and filtering technique and computer simulation. We established methods for preparing the protoplasts of Schizosaccharomyces pombe and conditions for the complete regeneration of the cell wall. The dynamic process of cell wall formation was clarified through our study of the protoplasts, using an improved ultra high resolution (UHR) FESEM S-900 and an S-900LV. It was found that β-1,3-glucan, β-1,6-glucan and α-1,3-glucan, as well as α-galactomannan, are ingredients of the cell wall. The process of septum formation during cell division was examined after cryo-fixation by high pressure freezing (HPF). It was also found that α-1,3- and β-1,3-glucans were located in the invaginating nascent septum, and later, highly branched β-1,6-glucan also appeared on the second septum. The micro-sampling method, using a focused ion beam (FIB), has been applied to our yeast cell wall research. A combination of FIB and scanning transmission electron microscopy is useful in constructing 3D images and analyzing the molecular architecture of cells, as well as for electron tomography of thick sections of biological specimens.

Virus-like particle production with yeast: ultrastructural and immunocytochemical insights into Pichia pastoris producing high levels of the hepatitis B surface antigen

BACKGROUND

A protective immune response against Hepatitis B infection can be obtained through the administration of a single viral polypeptide, the Hepatitis B surface antigen (HBsAg). Thus, the Hepatitis B vaccine is generated through the utilization of recombinant DNA technology, preferentially by using yeast-based expression systems. However, the polypeptide needs to assemble into spherical particles, so-called virus-like particles (VLPs), to elicit the required protective immune response. So far, no clear evidence has been presented showing whether HBsAg assembles in vivo inside the yeast cell into VLPs or later in vitro during down-stream processing and purification.

RESULTS

High level production of HBsAg was carried out with recombinant Pichia pastoris using the methanol inducible AOX1 expression system. The recombinant vaccine was isolated in form of VLPs after several down-stream steps from detergent-treated cell lysates. Search for the intracellular localization of the antigen using electron microscopic studies in combination with immunogold labeling revealed the presence of HBsAg in an extended endoplasmic reticulum where it was found to assemble into defined multi-layered, lamellar structures. The distance between two layers was determined as ~6 nm indicating that these lamellas represent monolayers of well-ordered HBsAg subunits. We did not find any evidence for the presence of VLPs within the endoplasmic reticulum or other parts of the yeast cell.

CONCLUSIONS

It is concluded that high level production and intrinsic slow HBsAg VLP assembly kinetics are leading to retention and accumulation of the antigen in the endoplasmic reticulum where it assembles at least partly into defined lamellar structures. Further transport of HBsAg to the Golgi apparatus is impaired thus leading to secretory pathway disfunction and the formation of an extended endoplasmic reticulum which bulges into irregular cloud-shaped formations. As VLPs were not found within the cells it is concluded that the VLP assembly process must take place during down-stream processing after detergent-mediated disassembly of HBsAg lamellas and subsequent reassembly of HBsAg into spherical VLPs.

Yeast and filamentous fungi as model organisms in microbody research

Yeast and filamentous fungi are important model organisms in microbody research. The value of these organisms as models for higher eukaryotes is underscored by the observation that the principles of various aspects of microbody biology are strongly conserved from lower to higher eukaryotes. This has allowed to resolve various peroxisome-related functions, including peroxisome biogenesis disorders in man. This paper summarizes the major advances in microbody research using fungal systems and specifies specific properties and advantages/disadvantages of the major model organisms currently in use.

The significance of peroxisomes in methanol metabolism in methylotrophic yeast

The capacity to use methanol as sole source of carbon and energy is restricted to relatively few yeast species. This may be related to the low efficiency of methanol metabolism in yeast, relative to that of prokaryotes. This contribution describes the details of methanol metabolism in yeast and focuses on the significance of compartmentalization of this metabolic pathway in peroxisomes.

Degradation of normal and proliferated peroxisomes in rat hepatocytes: regulation of peroxisomes quantity in cells

Degradation and turnover of peroxisomes is reviewed. First, we describe the historical aspects of peroxisome degradation research and the two major concepts for breakdown of peroxisomes, i.e., autophagy and autolysis. Next, the comprehensive knowledge on autophagy of peroxisomes in mammalian and yeast cells is reviewed. It has been shown that proliferated peroxisomes are degraded by selective autophagy, and studies using yeast cells have been especially helpful in shedding light on the molecular mechanisms of this process. The degradation of extraperoxisomal urate oxidase crystalloid is noted. Overexpressed wild-type urate oxidase in cultured cells has been shown to be degraded through an unknown proteolytic pathway distinct from the lysosomal system including autophagy or the ubiquitin-proteasome system. Finally, peroxisome autolysis mediated by 15-lipoxygenase (15-LOX) is described. 15-LOX is integrated into the peroxisome membrane causing focal membrane disruptions. The content of the peroxisomes is then exposed to cytosol proteases and seems to be digested quickly. In conclusion, the number of peroxisomes appears to be regulated by two selective pathways, autophagy, including macro- and microautophagy, and 15-LOX-mediated autolysis.

Production of lactones and peroxisomal beta-oxidation in yeasts

Among aroma compounds interesting for the food industry, lactones may be produced by biotechnological means using yeasts. These microorganisms are able to synthesize lactones de novo or by biotransformation of fatty acids with higher yields. Obtained lactone concentrations are compatible with industrial production, although detailed metabolic pathways have not been completely elucidated. The biotransformation of ricinoleic acid into gamma-decalactone is taken here as an example to better understand the uptake of hydroxy fatty acids by yeasts and the different pathways of fatty acid degradation. The localization of ricinoleic acid beta-oxidation in peroxisomes is demonstrated. Then the regulation of the biotransformation is described, particularly the induction of peroxisome proliferation and peroxisomal beta-oxidation and its regulation at the genome level. The nature of the biotransformation product is then discussed (4-hydroxydecanoic acid or gamma-decalactone), because the localization and the mechanisms of the lactonization are still not properly known. Lactone production may also be limited by the degradation of this aroma compound by the yeasts which produced it. Thus, different possible ways of modification and degradation of gamma-decalactone are described.

Divergent modes of autophagy in the methylotrophic yeast Pichia pastoris

The budding yeast Pichia pastoris responds to methanolic media by synthesizing high levels of cytosolic enzymes (e.g. formate dehydrogenase) and peroxisomal enzymes (e.g. alcohol oxidase), which are necessary to assimilate this carbon source. Major alterations in cellular metabolism are initiated upon a shift in carbon source to ethanol or glucose. These alterations require the synthesis of new proteins and the rapid degradation of those enzymes no longer needed for methanol utilization. In this study, we have measured cytosolic and peroxisomal enzyme activities and examined the fate of morphologically distinct peroxisomes to assess the degradative response of this yeast during nutrient adaptation. Utilizing biochemical, morphological and genetic approaches, we have shown that there exist in P. pastoris at least two pathways for the sequestration of peroxisomes into the vacuole for degradation. The ethanol-induced pathway is independent of protein synthesis and includes an intermediate stage in which individual peroxisomes are sequestered into autophagosomes by wrapping membranes, which then fuse with the vacuole. This process is analogous to macroautophagy. The glucose-induced pathway invokes the engulfment of clusters of peroxisomes by finger-like protrusions of the vacuole by a process analogous to microautophagy. Unlike ethanol adaptation, glucose stimulated the degradation of formate dehydrogenase as well. Peroxisomes remained outside the vacuoles of glucose-adapted cycloheximide-treated normal cells, suggesting that protein synthesis is required for peroxisome entry into the yeast vacuole. Two complementary mutants (gsa1 and gsa2) that are unable to degrade peroxisomes or formate dehydrogenase during glucose adaptation were isolated. The mutated gene products appear to function in one or more events upstream of degradation within the vacuole, since ethanol-induced peroxisome degradation proceeded normally in these mutants and peroxisomes were found outside the vacuoles of glucose-adapted gsa2 cells. Mutants lacking vacuolar proteinases A and B were unable to degrade alcohol oxidase or formate dehydrogenase during ethanol or glucose adaptation. Peroxisomes were found to accumulate within the vacuoles of these proteinase mutants during adaptation. Combined, the results suggest that there exist in Pichia pastoris two independent pathways for the sequestration of peroxisomes into the vacuole, the site of degradation.

Methanol oxidation and assimilation in Hansenula polymorpha. An analysis by 13C n.m.r. in vivo

The metabolism of methanol was monitored in whole cells of the methylotrophic yeast Hansenula polymorpha by using [13C]methanol and n.m.r. in vivo. The main products observed under normal conditions were trehalose and glycerol, whereas cells that were starved before exposure to [13C]methanol also accumulated glutamate, glutamine and alanine; formate was also more prominent in spectra from starved cells. Cells exposed to high methanol concentration together with high oxygenation oxidized methanol extensively, leading to formaldehyde accumulation; label was not found in any subsequent metabolic products, indicating possible cell inactivation. [13C]Formate was incorporated into metabolic products in glucose-grown cells exposed to 150 mM-methanol for 3 h, but not in cells starved for 3 h, in which it was oxidized. At 21 degrees C such 3 h-starved cells showed a slower metabolism of [13C]methanol compared with those at 37 degrees C, and also converted methanol into formate rather than into assimilation products. The labelling pattern in trehalose from starved cells at 37 degrees C was consistent with methanol assimilation via the pentose phosphate pathway. Lack of appearance of labelled formaldehyde and formate during metabolism under normal conditions suggests that the linear oxidation pathway is not a major contributor to methanol oxidation; their appearance in extreme conditions suggests instead a more likely role in detoxification.

Overexpression of alcohol oxidase in Pichia pastoris

The protein import capacity of peroxisomes in methylotrophic yeasts was studied using Pichia pastoris containing one or two extra copies of the gene encoding the peroxisomal protein alcohol oxidase. The alcohol oxidase overproduced in this strain was only partially imported and assembled into the active, octameric form of the protein. The excess remained in the cytosol as protein aggregates composed of monomers. These results are discussed in view of the possible application of peroxisomes as storage compartments for heterologous proteins.

Biosynthesis and assembly of alcohol oxidase, a peroxisomal matrix protein in methylotrophic yeasts: a review

Alcohol oxidase (AO) catalyses the first step of methanol metabolism in yeasts. In vivo the enzyme is compartmentalized in special cell compartments, called peroxisomes. The enzyme along with the organelles are induced during growth of methylotrophic yeasts on methanol as the sole carbon source. Like all other peroxisomal matrix proteins, AO is encoded by a nuclear gene. Expression of the protein is regulated by a repression/derepression mechanism, but also by induction. Inactive monomeric precursor protein is synthesized in the cytosol and subsequently imported post-translationally into peroxisomes without further processing. Assembly into the active homo-octameric enzyme and binding of the prosthetic group flavin adenine dinucleotide occurs inside the organelle. When enhanced concentration of octameric alcohol oxidase are present in the organelles, the enzyme may form a crystalloid. Oligomerization is not dependent on translocation of AO precursors into their target organelle since octameric, active AO is detected in the cytosol and nucleus of peroxisome-deficient mutants of Hansenula polymorpha: at high expression rates large cytosolic AO crystalloids are formed, which occasionally are also encountered inside the nucleus of such mutants. This paper summarizes recent findings and views on the mechanisms involved in synthesis, import, assembly and crystallization of this important peroxisomal enzyme.

Properties of catalase purified from a methanol-grown yeast, Kloeckera sp. 2201

Catalase, a marker enzyme of peroxisomes, was purified to homogeneity from whole cells of Kloeckera sp. 2201 (a strain of Candida boidinii) grown on methanol by means of ammonium sulfate fractionation followed by hydroxyapatite, Sephacryl S-300 and DEAE-Sepharose column chromatographies. Crystallized catalase was brown-coloured and needle-like. The molecular mass of the enzyme was about 240 000 daltons consisting of four identical subunits of 62 000 daltons. The minimum size of catalase molecule was estimated to be about 6 X 10 nm from an electron micrograph. Judging from the absorption spectrum, the enzyme seemed to belong to a group of T-type catalase. The Km value of the enzyme for hydrogen peroxide (catalatic activity) was 25 mM, while that for methanol (peroxidatic activity) was 83 mM. Catalase from Kloeckera sp. cells showed a certain degree of similarity to the enzyme purified from alkane-grown Candida tropicalis [T. Yamada et al. (1982) Eur. J. Biochem. 125, 517-521 and 129, 251-255] in its immunochemical properties.

Properties of catalase activity in vegetative and sporulating cells of yeast Saccharomyces cerevisiae

Properties of catalase activities have been examined in the intact cells of early stationary phase and cells 3 hr after transfer to sporulation medium in Saccharomyces cerevisiae. The catalase activities of the two cells had a broad optimal pH from 6 to 8. Catalase activity in the intact cells increased throughout a 4-hr period of the observation following transfer to sporulation medium. Almost all the catalase activity in vegetative cells was lost by the treatment at 60 degrees C for 10 min. Catalase activities of both cells were inhibited by KCN, NaN3, o-phenanthroline, and PCMB. The catalase activity of the vegetative cells was slightly more inhibited and inactivated than that of the sporulating cells by the inhibitors and by the treatment with HCl or NaOH.

Isolation of alcohol oxidase and two other methanol regulatable genes from the yeast Pichia pastoris

The oxidation of methanol follows a well-defined pathway and is similar for several methylotrophic yeasts. The use of methanol as the sole carbon source for the growth of Pichia pastoris stimulates the expression of a family of genes. Three methanol-responsive genes have been isolated; cDNA copies have been made from mRNAs of these genes, and the protein products from in vitro translations have been examined. The identification of alcohol oxidase as one of the cloned, methanol-regulated genes has been made by enzymatic, immunological, and sequence analyses. Methanol-regulated expression of each of these three isolated genes can be demonstrated to occur at the level of transcription. Finally, DNA subfragments of two of the methanol-responsive genomic clones from P. pastoris have been isolated and tentatively identified as containing the control regions involved in methanol regulation.

Isolation of alcohol oxidase and two other methanol regulatable genes from the yeast Pichia pastoris

The oxidation of methanol follows a well-defined pathway and is similar for several methylotrophic yeasts. The use of methanol as the sole carbon source for the growth of Pichia pastoris stimulates the expression of a family of genes. Three methanol-responsive genes have been isolated; cDNA copies have been made from mRNAs of these genes, and the protein products from in vitro translations have been examined. The identification of alcohol oxidase as one of the cloned, methanol-regulated genes has been made by enzymatic, immunological, and sequence analyses. Methanol-regulated expression of each of these three isolated genes can be demonstrated to occur at the level of transcription. Finally, DNA subfragments of two of the methanol-responsive genomic clones from P. pastoris have been isolated and tentatively identified as containing the control regions involved in methanol regulation.

Biosynthesis and regulation of the peroxisomal methanol oxidase from the methylotrophic yeast Hansenula polymorpha

The biosynthesis of methanol oxidase, a peroxisomal enzyme in the methanol-utilizing yeast Hansenula polymorpha, was studied in vitro. Translation of Hansenula mRNA in a rabbit reticulocyte lysate yields methanol oxidase protein in high amounts. The apparent molecular mass of the protein was found to be identical to the subunit of the functional multimeric enzyme, which indicates the absence of an N-terminal extension typical of most transported proteins. The regulation of methanol oxidase by glucose repression and depression as well as by induction of methanol was shown to be controlled at the level of transcription. Two mutants of Hansenula polymorpha, unable to grow on methanol as a carbon and energy source were shown to be affected in methanol oxidase synthesis.

Induction and subcellular localization of enzymes participating in propionate metabolism in Candida tropicalis

Candida tropicalis, a representative alkane- and higher fatty acid-utilizing yeast, can grow on propionate used as sole carbon and energy source. Initial pH of the medium markedly affected the growth of the yeast on propionate. In propionate-grown cells, several enzymes associated with peroxisomes and/or participating in propionate metabolism were induced in connection with the appearance of the characteristic peroxisomes. Acetate-grown cells of this yeast had only few peroxisomes, while alkane-grown cells contained conspicuous numbers of the organelles. As compared with alkane-grown cells, some specific features were observed in peroxisomes and enzymes associated with the organelles of propionate-grown cells: The shape of peroxisomes was large but the number was small; unlike localization of catalase in peroxisomes of alkane-grown cells, the enzyme of propionate-grown cells was mainly localized in cytoplasm; as for carnitine acetyltransferase localized almost equally in peroxisomes and mitochondria in alkane-grown cells, propionate-grown cells contained mainly the mitochondrial type enzyme. A propionate-activating enzyme, which was different from acetyl-CoA synthetase, was also induced in cytoplasm of propionate-grown cells. The role of carnitine acetyltransferase and the propionate-activating enzyme in propionate metabolism is discussed in comparison with the role of carnitine acetyltransferase and acetyl-CoA synthetase in acetate metabolism.

Substructure of crystalline peroxisomes in methanol-grown Hansenula polymorpha: evidence for an in vivo crystal of alcohol oxidase

The substructural organization of completely crystalline peroxisomes present in Hansenula polymorpha cells grown under methanol limitation in a chemostat was investigated by different cytochemical and ultrastructural techniques. Time-dependent cytochemical staining experiments indicated that activities of the two main constituents of these organelles, namely, alcohol oxidase and catalase, were present throughout the crystalline matrix. Catalase was completely removed from isolated peroxisomes by osmotic shock treatment. After such treatment, the ultrastructure of the crystalline matrix of the organelles remained virtually intact. Because alcohol oxidase activity was still present in this matrix, it was concluded that alcohol oxidase protein is the only structural element of the peroxisomal crystalloids. The molecular architecture of the crystalloids was investigated in ultrathin cryosections which permitted recognition of individual molecules in the crystalline matrix. Depending on the plane of sectioning, different crystalline patterns were observed. Tilting experiments indicated that these images were caused by superposition of octameric alcohol oxidase molecules arranged in a tetragonal lattice. A three-dimensional model of the crystalloid is presented. The repeating unit of this structure is composed of four alcohol oxidase molecules. The crystalloid represents an open structure, which may explain the observed free mobility of catalase molecules.

Three-dimensional structure of the crystalloid in the microbody of Kloeckera sp.: composite crystal model

Electron microscopic investigations using the cryosectioning technique, together with electron diffraction, optical diffraction, and computer simulation, were carried out for the determination of the intrinsic structure of the crystalloid in the microbody of Kloeckera sp. The lattice images seen in the cryosections could be changed from one to another by tilting the specimen at an appropriate angle, the images obtained being well consistent with those obtained by computer simulation. The electron diffraction patterns also agreed with those obtained by optical diffraction. The results demonstrated that the crystalloid was composed of two different types of particles, large and small ones, arranged alternately and making up the composite crystal of rock salt structure. Large particles seemed to consist of alcohol oxidase molecules, while the small particles were presumably made up of catalase molecules.

Enzyme activities during early ascosporulation in Saccharomyces cerevisiae

1. Several enzyme activities were examined during the initial sporulating phase in Saccharomyces cerevisiae. 2. Catalase activity increased obviously after transfer to sporulation medium. 3. Catalase is probably considered to play an essential role in sporulation. 4. Both activities of inorganic pyrophosphatase and glycerol-2-phosphatase decreased. 5. Conditions necessary for sporulation were suggested.

Partial purification and characterization of the multiple molecular forms of staphylococcal clotting activity (coagulase)

The clotting activity of Staphylococcus aureus strain 104 was purified 46,000-fold, but absolute purity was not achieved. Carbohydrate content of the purified material was not more than 5%. Elution of clotting activity from denaturing and nondenaturing polyacrylamide gels revealed the presence of four distinct molecular forms. Molecular weights of the forms were approximately 31,500, 34,800, 44,800, and 56,800 as determined by gel filtration in 8 M urea, by sodium dodecyl sulfate-urea polyacrylamide gel electrophoresis, and by calculation with determined values for the Stokes radius and sedimentation coefficient. Molecular weights determined on sodium dodecyl sulfate-urea gels were found to decrease as the gel concentration increased, suggesting that the amount of sodium dodecyl sulfate bound was less than normal. Estimated frictional ratios for the forms showed that they differ in shape from one another and that they are all highly asymmetrical. Each of the forms had an isoelectric point between pH 5.44 and 5.47 when focused in 6% polyacrylamide gels for 9 h; however, prolonged focusing altered the isoelectric point of the forms to within the range of pH 4.35 to 4.65. The multiple clotting forms were not artifacts of the purification procedure and did not appear to be products of the proteolytic degradation of a larger protein.

Substructure of crystalline peroxisomes in methanol-grown Hansenula polymorpha: evidence for an in vivo crystal of alcohol oxidase

The substructural organization of completely crystalline peroxisomes present in Hansenula polymorpha cells grown under methanol limitation in a chemostat was investigated by different cytochemical and ultrastructural techniques. Time-dependent cytochemical staining experiments indicated that activities of the two main constituents of these organelles, namely, alcohol oxidase and catalase, were present throughout the crystalline matrix. Catalase was completely removed from isolated peroxisomes by osmotic shock treatment. After such treatment, the ultrastructure of the crystalline matrix of the organelles remained virtually intact. Because alcohol oxidase activity was still present in this matrix, it was concluded that alcohol oxidase protein is the only structural element of the peroxisomal crystalloids. The molecular architecture of the crystalloids was investigated in ultrathin cryosections which permitted recognition of individual molecules in the crystalline matrix. Depending on the plane of sectioning, different crystalline patterns were observed. Tilting experiments indicated that these images were caused by superposition of octameric alcohol oxidase molecules arranged in a tetragonal lattice. A three-dimensional model of the crystalloid is presented. The repeating unit of this structure is composed of four alcohol oxidase molecules. The crystalloid represents an open structure, which may explain the observed free mobility of catalase molecules.

Ultrastructure of methanotrophic yeasts

The cellular structure of two yeast strains capable of growth on methane was investigated by electron microscopy. Microbodies were observed in cells of Sporobolomyces roseus strain Y and Rhodotorula glutinis strain CY when grown on methane but rarely when grown on glucose. The size of the microbodies and the number observed per cell in a thin section did not increase with culture age. No crystalline organization was observed within these organelles. Similar microbodies were also observed in cells of R. glutinis CY grown on hexadecane. The plasma membranes of both methane and hexadecane-grown cells exhibited increased invagination compared to that of glucose-grown cells. Catalase activity was detected in the microbodies of alkane-grown cells by using 3,3'-diaminobenzidine as a cytochemical stain. The data presented suggest that microbodies, and the catalase contained within them, play a role in eucaryotic methane metabolism.

An electron microscopical study of the development of peroxisomes during formation and germination of ascospores in the methylotrophic yeast Hansenula polymorpha

Ascospore formation was studied in liquid cultures of the yeast Hansenula polymorpha, previously grown under conditions in which the synthesis of alcohol oxidase was repressed (glucose as growth substrate) or derepressed (methanol, glycerol and dihydroxyacetone as growth substrates and after growth on malt agar plates). In ascospores obtained from repressed cells, generally one small peroxisome was present. The organelle probably originated from the small peroxisome, originally present in the vegetative cells. They had no crystalline inclusions and cytochemical experiments indicated the presence of catalase, urate oxidase and amino acid oxidase activities in these organelles. In ascospores obtained from derepressed cells, generally 1--3 crystalline peroxisomes were observed. These organelles also originated from the peroxisomes originally present in the vegetative cells by means of fragmentation or division. They contained, in addition to the enzymes characteristic for peroxisomes in spores from repressed cells, also alcohol oxidase. The latter enzyme is probably responsible for the crystalline substructure of these peroxisomes. Peroxisomes had no apparent physiological function in the process of ascosporogenesis. A glyoxysomal function of the organelles during germination of the ascospores was also not observed. Germination of mature ascospores in media containing different sources of carbon and nitrogen showed that the function of the peroxisomes present in ascospores of Hansenula polymorpha is probably identical to that in vegetative haploid cells. They are involved in the oxidative metabolism of different carbon and nitrogen sources. Their enzyme profile is a reflection of that peroxisomes of vegetative cells and their presence may enable the formation of cells which are optimally adapted to environmental conditions extant during spore germination.

Cytochemical localization of catalase and several hydrogen peroxide-producing oxidases in the nucleoids and matrix of rat liver peroxisomes

The distribution of catalase, amino acid oxidase, alpha-hydroxy acid oxidase, urate oxidase and alcohol oxidase was studied cytochemically in rat hepatocytes. The presence of catalase was demonstrated with the conventional diaminobenzidine technique. Oxidase activities were visualized with methods based on the enzymatic or chemical trapping of the hydrogen peroxide produced by these enzymes during aerobic incubations. All enzymes investigated were found to be present in peroxisomes. Catalase activity was found in the peroxisomal matrix, but also associated with the nucleoid. After staining for oxidase activities the stain deposits occurred invariably in the peroxisomal matrix as well as in the nucleoids. In all experiments the activity of both catalase and the oxidases was confined to the peroxisomes. The presence of a hydrogen peroxide-producing alcohol oxidase was demonstrated for the first time in peroxisomes in liver cells. The results imply that the enzyme activity of the nucleoids of rat liver peroxisomes is not exclusively due to urate oxidase. The nucleoids obviously contain a variety of other enzymes that may be more or less loosely associated with the insoluble components of these structures.

Development of a chemically defined liquid medium for growth of Legionella pneumophila

A chemically defined liquid medium has been developed for the study of the physiology and antigen production of the Legionnaires disease bacterium. The medium contains basal salts, vitamins, alpha-ketoglutaric acid, pyruvate, 0.05% l-cysteine, 0.05% glutathione, and a mixture of 20 additional amino acids, each of 0.01% final concentration, except serine, which was at 0.1%. The medium in shake culture at 37 degrees C with increased CO2 at pH 6.5, supports the maximum rate of growth, the highest cell yields, and the maximum cell surface antigen as distinguished by specific fluorescein isothiocyanate-conjugated antibody. Studies during the development of this medium showed that CO2, pyruvate, and alpha-ketoglutarate strongly stimulated growth; that cysteine and methionine were required for growth; and that serine, threonine, histidine, tyrosine, and tryptophane were energy sources. Glutathione substituted for cysteine, but cystine did not. The organisms did not use glucose and polysaccharides, as judged by cell yields when these carbohydrates were present or absent. The chelators malate, citrate, and ethylenediaminetetraacetic acid totally inhibited growth. Beta-mercaptoethanol, thioglycolate, dithiothreitol, and Tween 80 (0.05%) inhibited growth strongly or completely. Catalase activity was extremely weak or absent. Morphology varied, depending upon conditions and phases of growth. In general, filamentous forms became chains of cigar-shaped bacilli fragmenting to pairs and becoming coccoidal in the late stationary pha-e of growth. The organism grew at 25, 30, and 37 degrees C. Although they varied in their growth characteristics, 10 isolates were passed for five transfers in the chemically defined broth, giving maximum rates of growth, cell yields, and antigen production.

Subcellular localization of two long-chain acyl-coenzyme-A synthetases in Candida lipolytica

Studies have been made on the subcellular localization of two long-chain acyl-coenzyme-A synthetases as well as glycerolphosphate acyltransferase and the acyl-CoA-oxidizing system in Candida lipolytica grown on oleic acid. Acyl-CoA synthetase I is distributed among different subcellular fractions, including microsomes and mitochondria where glycerolphosphate acyltransferase is located. On the other hand, acyl-CoA synthetase II is localized in microbodies where the acyl-CoA-oxidizing system is located. These results support our previous conclusion that acyl-CoA synthetase I is responsible for the production of acyl-CoA to be utilized for the synthesis of cellular lipids, while acyl-CoA synthetase II provides acyl-CoA that is exclusively degraded via beta-oxidation.

Ribulose bisphosphate carboxylase from methanol-grown Paracoccus denitrificans

Paracoccus denitrificans grows on methanol as the sole source of energy and carbon, which it assimilates aerobically via the reductive pentose phosphate cycle. This gram-negative bacterium grew rapidly on 50 mM methanol (generation time, 7 h, 30 degrees C) in excellent yield (3 g of wet-packed cells per liter of culture). Electron microscopic studies indicated that the late-log-phase cells were coccoid, having a thick envelope surrounding a layer of more diffuse electron-dense material and a relatively electron-transparent core. Ribulose bisphosphate carboxylase in the 15,000 X g supernatant of fresh cells had specific activities (micromoles of CO2 fixed per minute per milligram of protein) of 0.026, 0.049, 0.085, 0.128, and 0.034 during the lag, early, mild-, and late log, and late stationary phases, respectively. The enzyme was purified 40-fold by pelleting at 159,000 X g, salting out, sedimentation into a 0.2 to 0.8 M linear sucrose gradient, and elution from a diethylaminoethyl-Sephadex column. The enzyme was homogeneous by the criteria of electrophoresis on polyacrylamide gels polymerized from several acrylamide concentrations and sedimentation behavior. The molecular weight of the native enzyme, as measured by gel electrophoresis and gel filtration, averaged 525,000. Sodium dodecyl sulfate dissociated the enzyme into two types of subunits with molecular weights of 55,000 and 13,600. The S20,w of the enzyme was 14.0 Km values for ribulose bisphosphate and CO2 were 0.166 and 0.051 mM, respectively, and the enzyme was inhibited to the extent of 94% by 1 mM 6-phosphogluconate.

Degradation of microbodies in relation to activities of alcohol oxidase and catalase in Candida boidinii

Degradation of microbodies in the methanol-utilizing yeast Candida boidinii was mainly studied by electron microscopical observation. The yeast cells precultured on methanol medium contained five to six microbodies per section and showed high activities of alcohol oxidase, catalase, formaldehyde dehydrogenase and formate dehydrogenase. When the precultured cells were transferred into an ethanol medium the number of microbodies and concomitantly the activities of alcohol oxidase and catalase decreased. After 6 h of cultivation microbodies were hardly detected. Also the activity of alcohol oxidase was not measurable and catalase activity was reduced to one tenth, whereas the activities of formaldehyde dehydrogenase and formate dehydrogenase decreased only to about 70%. Experiments with methanol-grown cells transferred into an ethanol medium without nitrogen source indicated that the inactivation of alcohol oxidase and catalase does not require protein synthesis. However, the reappearance of these enzymes is presumably due to de novo protein synthesis as shown by experiments with cycloheximide.

Immobilization of yeast microbodies by inclusion with photo-crosslinkable resins

Yeast microbodies containing FAD-dependent alcohol oxidase, catalase and D-amino acid oxidase were isolated from methanol-grown cells of Kloeckera sp. 2201 and immobilized intact in matrices formed by a short-time illumination of photo-crosslinkable resin oligomers. The relative activities of catalase, alcohol oxidase and D-amino acid oxidase of the gel-entrapped microbodies were 36, 76 and 31% respectively as compared with those of free microbodies. Immobilization enhance d the stability of catalase to a certain degree, but not that of alcohol oxidase. The pH/activity profiles of catalase and alcohol oxidase of the entrapped organelles showed more narrow pH optima than those of the free counterparts. D-Amino acid oxidase in immobilized microbodies showed a somewhat higher Km value for D-alanine than that in free ones. Immobilized microbodies oxidized two moles of methanol to form two moles of formaldehyde with consumption of one mole of molecular oxygen. Addition of 3-amino-1,2,4-triazole, an inhibitor of catalase, reduced the formation of formaldehyde to half the amount without change in the amount of oxygen consumed, indicating the synergic action of alcohol oxidase and catalase in methanol oxidation in the microbodies of living yeast cells.