Partial purification and characterization of the interconvertible forms of trehalase from Saccharomyces cerevisiae

Mechanism of neuroprotection by trehalose: controversy surrounding autophagy induction

Trehalose is a non-reducing disaccharide with two glucose molecules linked through an α, α-1,1-glucosidic bond. Trehalose has received attention for the past few decades for its role in neuroprotection especially in animal models of various neurodegenerative diseases, such as Parkinson and Huntington diseases. The mechanism underlying the neuroprotective effects of trehalose remains elusive. The prevailing hypothesis is that trehalose protects neurons by inducing autophagy, thereby clearing protein aggregates. Some of the animal studies showed activation of autophagy and reduced protein aggregates after trehalose administration in neurodegenerative disease models, seemingly supporting the autophagy induction hypothesis. However, results from cell studies have been less certain; although many studies claim that trehalose induces autophagy and reduces protein aggregates, the studies have their weaknesses, failing to provide sufficient evidence for the autophagy induction theory. Furthermore, a recent study with a thorough examination of autophagy flux showed that trehalose interfered with the flux from autophagosome to autolysosome, raising controversy on the direct effects of trehalose on autophagy. This review summarizes the fundamental properties of trehalose and the studies on its effects on neurodegenerative diseases. We also discuss the controversy related to the autophagy induction theory and seek to explain how trehalose works in neuroprotection.

Central Role of the Trehalose Biosynthesis Pathway in the Pathogenesis of Human Fungal Infections: Opportunities and Challenges for Therapeutic Development

Invasive fungal infections cause significant morbidity and mortality in part due to a limited antifungal drug arsenal. One therapeutic challenge faced by clinicians is the significant host toxicity associated with antifungal drugs. Another challenge is the fungistatic mechanism of action of some drugs. Consequently, the identification of fungus-specific drug targets essential for fitness in vivo remains a significant goal of medical mycology research. The trehalose biosynthetic pathway is found in a wide variety of organisms, including human-pathogenic fungi, but not in humans. Genes encoding proteins involved in trehalose biosynthesis are mechanistically linked to the metabolism, cell wall homeostasis, stress responses, and virulence of Candida albicans, Cryptococcus neoformans, and Aspergillus fumigatus. While there are a number of pathways for trehalose production across the tree of life, the TPS/TPP (trehalose-6-phosphate synthase/trehalose-6-phosphate phosphatase) pathway is the canonical pathway found in human-pathogenic fungi. Importantly, data suggest that proteins involved in trehalose biosynthesis play other critical roles in fungal metabolism and in vivo fitness that remain to be fully elucidated. By further defining the biology and functions of trehalose and its biosynthetic pathway components in pathogenic fungi, an opportunity exists to leverage this pathway as a potent antifungal drug target. The goal of this review is to cover the known roles of this important molecule and its associated biosynthesis-encoding genes in the human-pathogenic fungi studied to date and to employ these data to critically assess the opportunities and challenges facing development of this pathway as a therapeutic target.

Role of individual phosphorylation sites for the 14-3-3-protein-dependent activation of yeast neutral trehalase Nth1

Trehalases are important highly conserved enzymes found in a wide variety of organisms and are responsible for the hydrolysis of trehalose that serves as a carbon and energy source as well as a universal stress protectant. Emerging evidence indicates that the enzymatic activity of the neutral trehalase Nth1 in yeast is enhanced by 14-3-3 protein binding in a phosphorylation-dependent manner through an unknown mechanism. In the present study, we investigated in detail the interaction between Saccharomyces cerevisiae Nth1 and 14-3-3 protein isoforms Bmh1 and Bmh2. We determined four residues that are phosphorylated by PKA (protein kinase A) in vitro within the disordered N-terminal segment of Nth1. Sedimentation analysis and enzyme kinetics measurements show that both yeast 14-3-3 isoforms form a stable complex with phosphorylated Nth1 and significantly enhance its enzymatic activity. The 14-3-3-dependent activation of Nth1 is significantly more potent compared with Ca2+-dependent activation. Limited proteolysis confirmed that the 14-3-3 proteins interact with the N-terminal segment of Nth1 where all phosphorylation sites are located. Site-directed mutagenesis in conjunction with the enzyme activity measurements in vitro and the activation studies of mutant forms in vivo suggest that Ser60 and Ser83 are sites primarily responsible for PKA-dependent and 14-3-3-mediated activation of Nth1.

Characterization of alpha,alpha-trehalase released in the intestinal lumen by the probiotic Saccharomyces boulardii

OBJECTIVE

Trehalose intolerance due to alpha,alpha-trehalase deficiency has scarcely been studied. The purpose of this study was to measure alpha,alpha-trehalase activity in intestinal biopsy samples from 200 consecutive patients over a period of 6 months, and to characterize alpha,alpha-trehalase released by the probiotic Saccharomyces boulardii (S. boulardii).

MATERIAL AND METHODS

Enzyme activities were measured in human and rat intestinal mucosal samples using the micromethod of Messer & Dalqvist. alpha,alpha-trehalase from S. boulardii was immunoprecipitated and Western blotted using an IgG purified antibody raised against a 23 amino acid peptide of alpha,alpha-trehalase of S. cerevisiae.

RESULTS

Among 200 patients, most of whom complained of abdominal symptoms and diarrhoea, 18 (9%) had total alpha,alpha-trehalase deficiency (0-12 U/g mucosa) and 39 had partial deficiency (3-12 U/g mucosa). Only 4 patients (2%) presented selective alpha,alpha-trehalase deficiency with otherwise normal disaccharidases. Expressed per gram of powder, alpha,alpha-trehalase from S. boulardii delivered in vitro an activity 175 times higher than that of human trehalase per gram of intestinal mucosa. V(max) (22+/-0.43 micromol) and K(m) (5 mM) were close to that of the human enzyme, whereas Western blot revealed a signal of two subunits of 82 kDa. Finally, treatment of rats with S. boulardii resulted in increases in alpha,alpha-trehalase activities of 25 to 45% (p<0.01) in endoluminal fluid and intestinal mucosa compared with in controls.

CONCLUSIONS

Our data suggest that alpha,alpha-trehalase deficiency is more common than is believed and that oral administration of S. boulardii could be beneficial in patients with digestive symptoms caused by trehalose intolerance.

Biochemical characterisation of the trehalase of thermophilic fungi: an enzyme with mixed properties of neutral and acid trehalase

The trehalases from some thermophilic fungi, such as Humicola grisea, Scytalidium thermophilum, or Chaetomium thermophilum, possess mixed properties in comparison with those of the two main groups of trehalases: acid and neutral trehalases. Such as acid trehalases these enzymes are highly thermostable extracellular glycoproteins, which act at acidic pH. However, these enzymes are activated by calcium or manganese, and as a result inhibited by chelators and by ATP, properties typical of neutral trehalases. Here we extended the biochemical characterisation of these enzymes, by assaying their activity at acid and neutral pH. The acid activity (25-30% of total) was assayed in McIlvaine buffer at pH 4.5. Under these conditions the enzyme was neither activated by calcium nor inhibited by EDTA or ATP. The neutral activity was estimated in MES buffer at pH 6.5, after subtracting the activity resistant to EDTA inhibition. The neutral activity was activated by calcium and inhibited by ATP. On the other hand, the acid activity was more thermostable than the neutral activity, had a higher temperature optimum, exhibited a lower K(m), and different sensitivity to several ions and other substances. Apparently, these trehalases represent a new class of trehalases. More knowledge is needed about the molecular structure of this protein and its corresponding gene, to clarify the structural and evolutionary relationship of this trehalase to the conventional trehalases.

Purification and characterization of acid trehalase from muscle of Ascaris suum (Nematoda)

Acid trehalase (EC 3.2.1.28) was isolated from muscle of Ascaris suum by fractionating with ammonium sulfate, acetone and column chromatography on DEAE-cellulose and phenyl sepharose CL-4B. The purified homogeneous preparation of native acid trehalase exhibited a molecular mass of 76 kDa and of 38 kDa on SDS-PAGE. The enzyme has the optimum pH 4.9, pI 4.3, Km of 6.6 mM and Vmax=34.5 nM min(-1) x mg(-1). Besides trehalose, it hydrolyses sucrose, isomaltose and maltose and, to a lesser degree melezitose, and it does not act on cellobiose and lactose. Acid trehalase was activated by MgCl2, KNO3, NaCl, CaCl2, CH2ICOOH and p-chloromercuribenzoate and inhibited by EDTA, ZnSO4 and FeCl3.

Canatoxin, a toxic protein from jack beans (Canavalia ensiformis), is a variant form of urease (EC 3.5.1.5): biological effects of urease independent of its ureolytic activity

Canatoxin is a toxic protein from Canavalia ensiformis seeds, lethal to mice (LD(50)=2 mg/kg) and insects. Further characterization of canatoxin showed that its main native form (184 kDa) is a non-covalently linked dimer of a 95 kDa polypeptide containing zinc and nickel. Partial sequencing of internal peptides indicated homology with urease (EC 3.5.1.5) from the same seed. Canatoxin has approx. 30% of urease's activity for urea, and K(m) of 2-7 mM. The proteins differ in their affinities for metal ions and were separated by affinity chromatography on a Zn(2+) matrix. Similar to canatoxin, urease activates blood platelets and interacts with glycoconjugates. In contrast with canatoxin, no lethality was seen in mice injected with urease (10 mg/kg). Pretreatment with p-hydroxymercuribenzoate irreversibly abolished the ureolytic activity of both proteins. On the other hand, p-hydroxymercuribenzoate-treated canatoxin was still lethal to mice, and both treated proteins were fully active in promoting platelet aggregation and binding to glycoconjugates. Taken together, our data indicate that canatoxin is a variant form of urease. Moreover, we show for the first time that these proteins display several biological effects that are unrelated to their enzymic activity for urea.

The cyclic AMP/PKA signal pathway is required for initiation of spore germination in Schizosaccharomyces pombe

Spore germination, a transition from the quiescent G0 phase to the proliferation cycle, is triggered by glucose in Schizosaccharomyces pombe. The role of cAMP/protein kinase A (PKA) signalling in germination is investigated. Gene disruption of cyr1+, pka1+ and gpa2+ encoding adenylate cyclase, PKA and the alpha-subunit of a trimeric GTP-binding protein, respectively, reduced the colony-forming efficiency of spores in minimal medium. Isolated spores of these null mutants did not germinate in minimal medium for up to 12 h, at which time wild-type spores had completed germination and formed germ projections. In wild-type spores, cortical actin patches randomly distributed in the early stage of outgrowth and then localized to one side of spores before the formation of projections. In contrast, the mutant spores exhibited no actin patches, but the cell surface was predominantly stained, like ungerminated spores of wild-type. Flow fluorocytometric analysis of propidium iodide-stained spores revealed a distinct 1C DNA peak after germination was completed. The fluorescent profile of the mutant spores, however, did not change during 12 h incubation in the minimal medium. These observations indicate that spores harbouring either cyr1Delta, pka1Delta or gpa2Delta are hardly triggered to germination. When wild-type spores were exposed to glucose, the intracellular cAMP level transiently increased in a few minutes, but gpa2Delta spores did not respond to glucose. We conclude that S. pombe spores initiate germination in response to glucose through the cyclic AMP-PKA pathway.

Reserve carbohydrates metabolism in the yeast Saccharomyces cerevisiae

Glycogen and trehalose are the two glucose stores of yeast cells. The large variations in the cell content of these two compounds in response to different environmental changes indicate that their metabolism is controlled by complex regulatory systems. In this review we present information on the regulation of the activity of the enzymes implicated in the pathways of synthesis and degradation of glycogen and trehalose as well as on the transcriptional control of the genes encoding them. cAMP and the protein kinases Snf1 and Pho85 appear as major actors in this regulation. From a metabolic point of view, glucose-6-phosphate seems the major effector in the net synthesis of glycogen and trehalose. We discuss also the implication of the recently elucidated TOR-dependent nutrient signalling pathway in the control of the yeast glucose stores and its integration in growth and cell division. The unexpected roles of glycogen and trehalose found in the control of glycolytic flux, stress responses and energy stores for the budding process, demonstrate that their presence confers survival and reproductive advantages to the cell. The findings discussed provide for the first time a teleonomic value for the presence of two different glucose stores in the yeast cell.

Biotechnological applications of the disaccharide trehalose

Trehalose is a disaccharide present in a variety of anhydrobiotic organisms which have the ability to promptly resume their metabolism after addition of water. It has been successfully used as a nontoxic cryoprotectant of enzymes, membranes, vaccines, animal and plant cells and organs for surgical transplants. It has been predicted that trehalose can also be used as an ingredient for dried and processed food. Therefore, the recent biotechnological applications of trehalose have imposed the standardization of methods for its production, as well as for its specific quantification.

The role of the trehalose transporter during germination

Previous studies on the resistance of yeast cells to dehydration pointed towards the protective role of trehalose and the importance of the specific trehalose transporter in guaranteeing survival. The present report demonstrates that the trehalose transporter is essential during the germination process in order to translocate trehalose from the cytosol to the external environment. Diploids that lack the trehalose transporter germinate poorly and do not form 4 spore tetrads although they accumulate trehalose and show trehalase activity. Furthermore, addition of exogenous trehalose to the germination medium enhances germination and normal segregation. The ability to transport trehalose is dominant and seems to be related to a single gene.

Molecular biology of trehalose and the trehalases in the yeast Saccharomyces cerevisiae

The present state of knowledge of the role of trehalose and trehalose hydrolysis catalyzed by trehalase (EC 3.2.1.28) in the yeast Saccharomyces cerevisiae is reviewed. Trehalose is believed to function as a storage carbohydrate because its concentration is high during nutrient limitations and in resting cells. It is also believed to function as a stress metabolite because its concentration increases during certain adverse environmental conditions, such as heat and toxic chemicals. The exact way trehalose may perform the stress function is not understood, and conditions exist under which trehalose accumulation and tolerance to certain stress situations cannot be correlated. Three trehalases have been described in S. cerevisiae: 1) the cytosolic neutral trehalase encoded by the NTH1 gene, and regulated by cAMP-dependent phosphorylation process, nutrients, and temperature; 2) the vacuolar acid trehalase encoded by the ATH1 gene, and regulated by nutrients; and 3) a putative trehalase Nth1p encoded by the NTH2 gene (homolog of the NTH1 gene) and regulated by nutrients and temperature. The neutral trehalase is responsible for intracellular hydrolysis of trehalose, in contrast to the acid trehalase, which is responsible for utilization of extracellular trehalose. The role of the putative trehalase Nth2p in trehalose metabolism is not known. The NTH1 and NTH2 genes are required for recovery of cells after heat shock at 50 degrees C, consistent with their heat inducibility and sequence similarity. Other stressors, such as toxic chemicals, also induce the expression of these genes. We therefore propose that the NTH1 and NTH2 genes have stress-related function and the gene products may be called stress proteins. Whether the stress function of the trehalase genes is linked to trehalose is not clear, and possible mechanisms of stress protective function of the trehalases are discussed.

Trehalase of Dictyostelium discoideum: inhibition by amino-containing analogs of trehalose and affinity purification

The inhibitory effects of three nitrogen containing analogs of trehalose, validamycin A, MDL 25,637 and castanospermine, on Dictyostelium discoideum trehalase were examined. Prior to this study, the effects of glycohydrolase inhibitors on D discoideum trehalase have not been reported. Validamycin A, MDL 25,637 and castanospermine were found to be potent, reversible, competitive inhibitors of D discoideum vegetative trehalase in vitro with IC50 values of 1 x 10(-9) M, 2 x 10(-8) M and 1.25 x 10(-4) M, respectively. Validamycin A and MDL 25,637 also exhibited time-dependent inhibition of D discoideum trehalase, whereby the potencies of these two inhibitors were observed to increase when pre-incubated with the enzyme for up to 60 min. The competitive natures of validamycin A and MDL 25,637 were also altered during pre-incubation with enzyme such that the compounds behaved as mixed inhibitors under these conditions. Taken together, these results suggest that the inhibitory action of validamycin A and MDL 25,637 on trehalase is of a slow-binding nature. A trehalase-specific affinity resin was synthesized by covalently coupling validamycin A to Sepharose 6B. This resin was used to purify D discoideum trehalase to near homogeneity in a two-step procedure. SDS-PAGE of affinity-purified trehalase, and silver staining or in situ staining for trehalase activity, revealed a major protein species of 42 kDa, exhibiting trehalase activity, and two minor protein species of approximately 45 and 49 kDa. Since validamycin A demonstrates strict binding specificity for trehalase, validamycin A-Sepharose has potential and novel applications in rapid, large scale, purification of trehalases from a variety of species origins.

Modulation of trehalase activity in Saccharomyces cerevisiae by an intrinsic protein

The regulation of cytosolic trehalase activity in yeast has been described as cycles of activation by phosphorylation by cAMP protein kinase. In this paper, evidence is presented for another regulatory mechanism--the binding of an endogenous inhibitory protein. This negative modulator was isolated during the purification procedure of cytosolic cryptic trehalase from repressed wild-type cells of Saccharomyces cerevisiae. However, in derepressed cells the inhibitor was not found nor was it present in ras2 mutant cells submitted to a heat treatment. The trehalase inhibitory activity proved to be a calmodulin ligand protein and, therefore, involved in the modulation of trehalase activity by Ca2+ ions.

Characterisation of an acid trehalase of Saccharomyces cerevisiae present in trehalase-sucrase aggregate

An acid trehalase-sucrase aggregate was purified (by 780-fold) from Saccharomyces cerevisiae, following conventional protein purification techniques, to an apparent yield of 18.5%. The aggregate was electrophoretically homogeneous but contained 175, 90, 68, 60, 40 molar mass (kDa) bands on SDS-electrophoresis. The purified aggregate had a specific activity (acid trehalase) of 22 U/mg; a Km value of 5.0 mM but contained 3-times more sucrase activity. Only sucrose and trehalose were hydrolysed by this aggregate and both activities were inhibited by acetate or phosphate. Temperature and pH optima for trehalose hydrolysis appeared to be 40-45 degrees C and 5.0, respectively. The purified aggregate appeared to be disaggregating spontaneously resulting in inactivation of both enzymes, which was enhanced either at pH 3.5 or at pH 7.0. Separation of acid trehalase from the aggregate by hydrophobic interaction chromatography resulted in inactivation. Rechromatography (HPGPLC) of the purified aggregate also gave disaggregation as well as inactivation of both enzymes. Disaggregated acid trehalase and sucrase contained 20-fold and 13-fold lower specific activities, respectively, and appeared to be unstable. Based on these observations we suggest that acid trehalase is stabilised by aggregation with sucrase.

Comparative study of two trehalase activities from Fusarium oxysporum var. lini

Acid and neutral trehalase activities (optimum pH of 4.6 and 6.8, respectively) from Fusarium oxysporum var. lini were studied separately through partial isolation by ammonium sulfate precipitation followed by ion-exchange chromatography on DEAE-Sephacel for neutral enzyme, or using some of their differential properties. Acid activity was unaffected by 1 mM of Ca2+, Mg2+, Mn2+, Ba2+, or EDTA. Contrarily, the neutral enzyme was activated by Ca2+ with an apparent Ka of 0.15 mM; was inhibited by EDTA, Zn2+, Hg2+, or Mg(2+)-ATP; and showed an increase in activity by the raise of buffer ionic strength or by the addition of 100 mM KCl. Acid and neutral enzymes have, respectively, an apparent optimum temperature of 45 and 30 degrees C, an apparent Km for trehalose of 0.43 and 8.45 mM, and an apparent M(r) of 160,000 and 100,000 (by glycerol gradient ultracentrifugation). Acid trehalase was specifically inhibited by acetate buffer and more stable at 50 degrees C than the neutral enzyme. Neutral enzyme exhibited a pI of 6.2 by isoelectric focusing. Contrary to neutral trehalases from other fungi, the enzyme from Fusarium oxysporum var. lini was not activated in crude extract by treatment with Mg(2+)-ATP in the presence of cAMP and not inactivated by alkaline phosphatase from Escherichia coli.

Trehalose metabolism in Saccharomyces cerevisiae during heat-shock

When different strains of Saccharomyces cerevisiae grown at 23 degrees C were transferred to 36 degrees C, trehalose and glycogen were accumulated. Glycogen accumulation was less extensive and its synthesis started at least 15 min after initiation of trehalose synthesis. The steady-state intracellular concentration of trehalose increased simultaneously with the activities of the enzymes trehalose-6P synthase, UDPG-pyrophosphorylase, phosphoglucomutase and trehalase. A small but significant change was observed in hexokinase activity. Our results directly implicate isoform PII of hexokinase and the minor isoform of phosphoglucomutase in the pathway of trehalose formation during heat-shock. We also showed that the major isoform of phosphoglucomutase increased in activity but was not essential for trehalose accumulation. Studies with the glucose uptake system indicated that trehalose accumulation could be primarily determined by intracellular availability of substrates due to the increase in the rate of glucose uptake. The increased uptake appears to have two components: a kinetic effect of temperature upon glucose transporters and an increase in the numbers of molecules of the transporters, probably mediated by synthesis de novo.

Differential changes in the activity of cytosolic and vacuolar trehalases along the growth cycle of Saccharomyces cerevisiae

Saccharomyces cerevisiae cells contain two intracellular and soluble trehalases with distinct subcellular location (cytosol and vacuoles, respectively). Both enzymes showed an opposite pattern of activity along the growth cycle. Activity of the cytosolic trehalase was high in cells growing exponentially on fermentable sugars (glucose, mannose or galactose) and sharply decayed as the cultures enter stationary phase coinciding with the beginning of trehalose biosynthesis. By contrast, vacuolar trehalase was only detectable in glucose-grown resting cells or in cultures growing on respiratory substrates (glycerol or ethanol). This enzyme was partially derepressed in the mutant hex2, which is deficient in glucose repression. Addition of fresh YPD medium to stationary-phase cultures induced the sudden reactivation of cytosolic trehalase with the concomitant slower inactivation of vacuolar trehalase. However, addition of glucose or various nitrogen sources alone had only a minor effect on both activities. The presence of cycloheximide had no effect on cytosolic trehalase, whereas completely blocked the appearance of vacuolar trehalase suggesting the requirement of protein synthesis 'de novo'.

The interaction of Saccharomyces cerevisiae trehalase with membranes

Plasma membranes isolated from cells of Saccharomyces cerevisiae previously submitted to a heat-shock showed a 10-fold increase in membrane-bound trehalase activity. Trehalase was purified to a high specific activity and was shown to be inhibited by glucose 6-phosphate and by the addition of a neutral phospholipid-like surfactant. Purified trehalase binds spontaneously to egg phosphatidylcholine small unilamellar vesicles, when in its active, phosphorylated form. When the enzyme was treated with alkaline phosphatase no binding was observed. The significance of this reversible binding for the control of trehalose metabolism in yeast cells is still unknown.

The control of trehalose biosynthesis in Saccharomyces cerevisiae: evidence for a catabolite inactivation and repression of trehalose-6-phosphate synthase and trehalose-6-phosphate phosphatase

During diauxic growth of yeast in glucose-rich medium, the accumulation of trehalose started well after complete exhaustion of glucose from the medium. The accumulation of the disaccharide was concomitant with a resumption of cell growth on the ethanol accumulated in the medium, but not with a degradation of glycogen which occurred as soon as glucose had been consumed. In contrast, in a mutant deficient in phosphoenolpyruvate carboxykinase, the synthesis of trehalose coincided exactly with the degradation of glycogen. Upon inoculation of stationary phase wild-type cells into a glucose medium, the activities of trehalose-6-phosphate (Tre6P) synthase and Tre6P phosphatase dropped in parallel to reach only 15% of their initial values after 3 h, and only recovered their original values as cells re-entered stationary phase. In the presence of cycloheximide, the decrease in Tre6P synthase and Tre6P phosphatase activities was restricted to 50-60%, the remaining decrease being inhibited by the drug. Furthermore, the reappearance of the enzyme activities following transfer of cells to an acetate medium was blocked by cycloheximide. It was also shown that loss of activity of these two enzymes required a combination of metabolizable sugars together with a nitrogen source. Low activities of Tre6P synthase and Tre6P phosphatase were measured in mutants with increased adenylate cyclase activity (RAS2ala18val19 mutants). Moreover, derepression of these enzymes at the approach of stationary phase was prevented in a pde2 mutant when it was cultivated in the presence of exogenous cyclic nucleotide. The mechanism of this effect is not clear, but may involve a transcriptional regulation by cAMP of the genes encoding these proteins.

Partial purification and characterization of trehalase from axenically grown myxamoebae of Dictyostelium discoideum

Lysosomal trehalase from the myxamoebae of Dictyostelium discoideum has been partially purified. The behavior of the enzyme under different chromatographic and electrophoretic conditions reveals its close similarities to other lysosomal enzymes that have been studied earlier. The cellular trehalase, which is electrophoretically homogeneous, appears as two peaks of activity when subjected to hydroxyapatite and gel filtration chromatography. The enzyme has isoelectric points of 4.0 and less than 2.5. Among natural disaccharides tested, the purified trehalase showed absolute specificity for trehalose with an apparent Km of 1.15 mM. However, the enzyme efficiently utilized the synthetic sugar alpha-D-glucosyl fluoride as a substrate. Various methods were employed to estimate the apparent molecular weight, which was found to lie in the range of 30-162 kDa.

Regulation of trehalose metabolism by Streptomyces griseus spores

Spores of Streptomyces griseus contain trehalose and trehalase, but trehalose is not readily hydrolyzed until spore germination is initiated. Trehalase in crude extracts of spores, germinated spores, and mycelia of S. griseus had a pH optimum of approximately 6.2, had a Km value for trehalose of approximately 11 mM, and was most active in buffers having ionic strengths of 50 to 200 mM. Inhibitors or activators or trehalase activity were not detected in extracts of spores or mycelia. Several lines of evidence indicated that trehalose and trehalase are both located in the spore cytoplasm. Spores retained their trehalose and most of their trehalase activity following brief exposure to dilute acid. Protoplasts formed by enzymatic removal of the spore walls in buffer containing high concentrations of solutes also retained their trehalose and trehalase activity. Protoplasts formed in buffer containing lower levels of solutes contained low levels of trehalose. The mechanism by which trehalose metabolism is regulated in S. griseus spores is unresolved. A low level of hydration of the cytoplasm of the dormant spores and an increased level of hydration during germination may account for the apparent inactivity of trehalase in dormant spores and the rapid hydrolysis of trehalose upon initiation of germination.

Purification of delta-aminolevulinate dehydratase from genetically engineered yeast

Saccharomyces cerevisiae transformed with a multicopy plasmid carrying the yeast structural gene HEM2, which codes for delta-aminolevulinate dehydratase, was enriched 20-fold in the enzyme. Beginning with cell-free extracts of transformed cells, the dehydratase was purified 193-fold to near-homogeneity. This represents a 3900-fold purification relative to the enzyme activity in normal, untransformed yeast cells. The specific activity of the purified enzyme was 16.2 mumol h-1 per mg protein at pH 9.4 and 37.5 degrees C. In most respects the yeast enzyme resembles mammalian enzymes. It is a homo-octamer with an apparent Mr of 275,000, as determined by centrifugation in glycerol density gradients, and under denaturing conditions behaved as a single subunit of Mr congruent to 37,000. The enzyme requires reduced thiol compounds to maintain full activity, and maximum activity was obtained in the presence of 1.0 mM-Zn2+. It is sensitive to inhibition by the heavy metal ions Pb2+ and Cu2+. The enzyme exhibits Michaelis-Menten kinetics and has an apparent Km of 0.359 mM. Like dehydratases from animal tissues, the yeast enzyme is rather thermostable. During the purification process an enhancement in total delta-aminolevulinate dehydratase activity suggested the possibility that removal of an inhibitor of the enzyme could be occurring.

Trehalose levels and survival ratio of freeze-tolerant versus freeze-sensitive yeasts

Five freeze-tolerant yeast strains suitable for frozen dough were compared with ordinary commercial bakers' yeast. Kluyveromyces thermotolerans FRI 501 cells showed high survival ability after freezing when their resting cells were fermented for 0 to 180 min in modified liquid medium, and they grew to log and stationary phases. Among the freeze-tolerant strains of Saccharomyces cerevisiae, FRI 413 and FRI 869 showed higher surviving and trehalose-accumulating abilities than other S. cerevisiae strains, but were affected by a prolonged prefermentation period and by growth phases. The freeze tolerance of the yeasts was, to some extent, associated with the basal amount of intracellular trehalose after rapid degradation at the onset of the prefermentation period. In the freeze-sensitive yeasts, the degree of hydrolysis of trehalose may thus be affected by the kind of saccharide, unlike in freeze-tolerant yeasts.

Lipoamidase (lipoyl-X hydrolase) from pig brain

Although the optimum substrate for lipoamidase (lipoyl-X hydrolase) has not yet been determined, it is known that lipoamidase activity, as determined by hydrolysis of the synthetic substrate lipoyl 4-aminobenzoate (LPAB), is widely distributed in pig brain tissues, i.e. in the cerebrum, cerebellum and medulla. Over 95% of the enzyme activity is present in the membrane subfractions, indicating that brain lipoamidase is an integral membrane protein enzyme. To elucidate the chemical nature and the optimum substrate of the abundant lipoamidase in the brain, we isolated it from the membrane subfractions. After an 8-step purification procedure, brain lipoamidase was purified 601-fold and identified as a 140 kDa glycoprotein by SDS/PAGE. A mechanistic study to determine Km and Vmax, values was carried out using various synthetic compounds. Lipoyl-lysine, which is generally believed to be a naturally occurring substrate of lipoamidase, was first compared with biotinyl-lysine, because these two vitamins have reactive sulphur atoms and are similar in molecular mass and structure. The Km for lipoyl-lysine was 333 microM, whereas biotinyl-lysine was not hydrolysed. Stringent specificity for the lipoyl moiety is demonstrated, as expected. Dipeptides of amino acid-lysine structures were studied, and dipeptides of aspartyl- and glutamyl-lysine hydrolysis occurred at high Km (3 mM) values. Thus lysine in the moiety is not very effective as an optimum substrate. The chemical bond structures of the amide bond (lipoyl-lysine) and peptide bond (aspartyl-lysine) were hydrolysed. Next, the ester bond compound was tested, and it was observed that lipolylmethyl ester was hydrolysed at high specificity. These findings indicate that this enzyme has broad specificities with respect to bond structure; it therefore is a unique hydrolase having stringent specificity for lipoic acid and relatively broad specificity for the chemical bond and the X moiety. Various inhibitors were tested; a few reagents, such as organic mercurials, di-isopropylfluorophosphate, 1,10-phenanthroline, sodium azide and angiotensin-converting enzyme inhibitor exhibited some inhibition (not more than 60%). Thus the active centre of this enzyme is a complex type. Although ATP is not hydrolysed and the lowest Km value is exhibited by the synthetic substrate reduced from LPAB (12 microM), some other compounds may still be expected to be hydrolysed by this unique and abundant brain lipoamidase.

Identification of an ADPG-dependent trehalose synthase in Saccharomyces

Uridine diphosphoglucose is not the sole donor for trehalose synthesis in yeast cells: an ADPG-dependent trehalose synthase, has been identified in mutant strains with undetectable UDPG-dependent trehalose-6-P synthase activity. Genetic and chromatographic studies indicate that the two activities correspond to different proteins. The apparent Km for the nucleotide is similar for both enzymes, and Mg2+ is also required for both activities; however, a striking difference was observed with respect to ATP.Mg activation. This newly determined enzymatic activity in Saccharomyces clarifies previous contradictory results with mutant strains that are able to accumulate trehalose during growth yet whose UDPG-dependent trehalose synthase activity is undetectable in vitro.

Determination of trehalose in biological samples by a simple and stable trehalase preparation

A three step purification procedure for trehalase from Saccharomyces cerevisiae with a recovery of 76% of the original activity is presented. The enzyme was activated by a heat shock treatment prior to homogenization of the cells. A mutant strain deleted in SUC genes was used to avoid contamination by invertase. The lyophylized enzyme was stable for, at least, 5 months and could be used to determine trehalose in the range 25 to 500 nmol. The preparation was free of inspecific phosphatases allowing for trehalose determinations in yeast cell free extracts and in insect hemolymph.

Changes in activities of several enzymes involved in carbohydrate metabolism during the cell cycle of Saccharomyces cerevisiae

Activity changes of a number of enzymes involved in carbohydrate metabolism were determined in cell extracts of fractionated exponential-phase populations of Saccharomyces cerevisiae grown under excess glucose. Cell-size fractionation was achieved by an improved centrifugal elutriation procedure. Evidence that the yeast populations had been fractionated according to age in the cell cycle was obtained by examining the various cell fractions for their volume distribution and their microscopic appearance and by flow cytometric analysis of the distribution patterns of cellular DNA and protein contents. Trehalase, hexokinase, pyruvate kinase, phosphofructokinase 1, and fructose-1,6-diphosphatase showed changes in specific activities throughout the cell cycle, whereas the specific activities of alcohol dehydrogenase and glucose-6-phosphate dehydrogenase remained constant. The basal trehalase activity increased substantially (about 20-fold) with bud emergence and decreased again in binucleated cells. However, when the enzyme was activated by pretreatment of the cell extracts with cyclic AMP-dependent protein kinase, no significant fluctuations in activity were seen. These observations strongly favor posttranslational modification through phosphorylation-dephosphorylation as the mechanism underlying the periodic changes in trehalase activity during the cell cycle. As observed for trehalase, the specific activities of hexokinase and phosphofructokinase 1 rose from the beginning of bud formation onward, finally leading to more than eightfold higher values at the end of the S phase. Subsequently, the enzyme activities dropped markedly at later stages of the cycle. Pyruvate kinase activity was relatively low during the G1 phase and the S phase, but increased dramatically (more than 50-fold) during G2. In contrast to the three glycolytic enzymes investigated, the highest specific activity of the gluconeogenic enzyme fructose-1, 6-diphosphatase 1 was found in fractions enriched in either unbudded cells with a single nucleus or binucleated cells. The observed changes in enzyme activities most likely underlie pronounced alterations in carbohydrate metabolism during the cell cycle.

Regulation of the trehalose-6-phosphate synthase complex in Saccharomyces. I. Interconversion of forms by phosphorylation

Trehalose-6-phosphate synthase is another example of an enzyme of carbohydrate metabolism, in Saccharomyces, which could be regulated by interconversion of forms. Deactivation was mediated both in vivo and in vitro by a cyclic AMP-dependent protein kinase. Reversibility of this process was obtained by a phosphatase treatment leading to an increase in activity. The phosphorylated, less active form of the enzyme proved to be more susceptible to activation by ATP.Mg. Mutants with well defined lesions in the cyclic AMP-dependent protein kinase system were used to corroborate our findings of a possible regulatory mechanism of trehalose-6-phosphate synthase activity by interconversion of forms.