Effect of ammonium ions on activity of hydrolytic enzymes during sporulation of yeast

Characterization and localization of the sporulation glucoamylase of Saccharomyces cerevisiae

Glucoamylase (SGA) was purified approximately 250-fold from sporulating Saccharomyces cerevisiae cells. The partially purified enzyme was active against glycogen, starch, maltotriose and maltose. It exhibited maximum catalytic activity against glycogen at pH 5.5. The enzyme appears to be glycosylated, because it bound to lentil-lectin Sepharose. SGA was expressed in vegetatively growing cells under the control of the GAL1 promoter, and the cellular location of the enzymatic activity determined by fractionation techniques. SGA was preferentially recovered in fractions which were enriched for the vacuolar hydrolases, carboxypeptidase Y and alpha-mannosidase.

Ammonia: its effects on biological systems, metabolic hormones, and reproduction

The physical, chemical properties of ammonia, its sources and detoxification, its effects in biological systems, its influence upon insulin action and glucose metabolism, and its possible effects on reproduction are discussed. Present chemical methods do not distinguish nonionic from ionic forms. At physiological pH, nonionic ammonia concentrations remain low but are primarily responsible for toxic effects. Thus, biologically significant changes of ammonia concentrations may not be revealed by determinations of ammonia in blood plasma. For these and other reasons the subacute toxicity of ammonia often is unrecognized, and its effects on intermediary metabolism and the hormonal milieu in normal and disease states remain poorly understood. Effects of ammonia may be stimulatory at low concentrations and inhibitory as concentrations rise or exposure is extended. Extensive experiments in eight ureotelic species, including man, show that urinary excretion of orotic acid becomes significantly elevated when the quantity of ammonia presented to the liver exceeds the capacity for normal detoxification. Present evidence with arginine and other intermediates of the urea cycle suggest that these substances influence glucose metabolism and insulin action. Recent studies of dairy cattle provide speculative evidence that high protein feeding or forms of protein that lead to elevated ammonia concentrations in tissue decrease conception rates and increase the calving to conception interval of dairy cows. Limited data concerning luteinizing hormone concentrations and steroid hormone metabolism are insufficient to establish whether differences in reproductive performance are due to changes of hormonal physiology, intrauterine environment, or metabolism.

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.

A particulate form of alkaline phosphatase in the yeast, Saccharomyces cerevisiae

A new form of alkaline phosphatase (orthophosphoric-monoester phosphohydrolase (alkaline optimum), EC 3.1.3.1) has been identified in the yeast Saccharomyces cerevisiae. Utilizing either synthetic or natural substrates, the enzyme exhibited a broad pH activity curve with maximum activity between 8.5 and 9.0. The enzyme was nonspecific with respect to substrate, attacking a variety of compounds containing phosphomonoester linkages, but has no detectable activity against polyphosphate, pyrophosphate or phosphodiester linkages. The enzyme exhibited an apparent Km of 0.25 mM with respect to p-nitrophenyl phosphate, 0.38 mM with respect to alpha-naphthyl phosphate, and 1.0 mM with respect to 5'AMP. The enzyme is regulated in a constitutive manner and its activity does not increase during phosphate starvation or sporulation, as does the repressible alkaline phosphatase. The enzyme is tightly bound to a particulate fraction of the cell, tentatively identified as the tonoplast membrane. It is not solubilized by treatment with high concentrations of NaCl, KH2PO4 or chaotropic agents. Triton X-100 (0.1%) solubilizes 12% of the particulate activity. This enzyme is differentiated from the other alkaline phosphatases found in yeast by its chromatographic elution DEAE-cellulose, kinetic parameters, heat stability and pH stability, as well as its particulate nature. This particulate alkaline phosphatase was found in every strain examined. It has a significantly lower specific activity in the phoH mutant and a higher activity in the acid phosphatase constitutive mutant A137.

Sporulation in Hansenula wingei is induced by nitrogen starvation in maltose-containing media

The sexually agglutinative yeast Hansenula wingei lives in association with bark beetles that inhabit coniferous trees. This yeast was induced to sporulate by malt extract, which contains a high percentage of maltose (50%) and a low percentage of nitrogen (0.5%). A solution of 1.5% maltose without any growth factors also induced ascosporogenesis in H. wingei. Thus, only a carbon source is required for sporulation as in Saccharomyces. However, potassium acetate did not induce sporulation in H. wingei as it does in S. cerevisiae. Instead, disaccharides (such as maltose, sucrose, or cellobiose) promote sporulation better than either monosaccharides (such as dextrose, fructose, or mannose) or respiratory substrates (such as ethanol or glycerol). The specificity of disaccharides in promoting sporulation in H. wingei may be considered an adaptation since these disaccharides are present in the natural environment of this yeast. In addition, the specificity of disaccharides may be related to the induction of the disaccharidase because cells precultured on dextrose sporulate well on maltose, but cells precultured on maltose sporulate poorly on maltose. When (NH(4))(2)SO(4) was added at a low concentration (3 mM) to synthetic sporulation medium (1.5% maltose solution), sporulation was abolished, whereas other salts and nitrogen sources inhibited to a lesser extent and vitamins and trace elements had no effect. Oxygen was required for sporulation, as expected for an obligate aerobe. Maximal sporulation was achieved in 2% malt extract broth at high cell density (10(9) cells per ml), pH 5, and 25 degrees C. By using these optimal physiological conditions and hybrid strains selected from an extensive genetic breeding program, about 30% asci (10% tetrads) were obtained routinely. Thus, the genetics of cell recognition in this yeast can now be studied.