Net phosphate transport in phosphate-starved Candida utilis: relationships with pH and K+

Oxygen regulation of alternative respiration in fungus Phycomyces blakesleeanus: connection with phosphate metabolism

Environmental changes can often result in oxygen deficiency which influences cellular energy metabolism, but such effects have been insufficiently studied in fungi. The effects of oxygen deprivation on respiration and phosphate metabolites in Phycomyces blakesleeanus were investigated by oxygen electrode and (31)P NMR spectroscopy. Mycelium was incubated in hypoxic and anoxic conditions for 1.5, 3 and 5 h and then reoxygenated. Participation of alternative oxidase (AOX) in total respiration increased gradually in both treatments and after 5 h of anoxia exceeded a value 50% higher than in control. Shortly after reintroduction of oxygen into the system AOX level decreased close to the control level. Oxygen deprivation also caused a reversible decrease of polyphosphate/inorganic phosphate ratio (PPc/Pi), which was strongly correlated with the increase of AOX participation in total respiration. Unexpectedly, ATP content remained almost constant, probably due to the ability of PolyP to sustain energy and phosphate homeostasis of the cell under stress conditions. This was further substantiated by the effects of azide, a cytochrome c oxidase inhibitor, which also decreased PPc/Pi ratio, but to a smaller extent in oxygen deprived than control and reoxygenated specimens.

Effects of anoxia on 31P NMR spectra of Phycomyces blakesleeanus during development

The method of 31P NMR spectroscopy was used to investigate the effects of anoxia on Phycomyces blakesleea?nus mycelium during development. The greatest changes were recorded in the PPc, NADH, and ?-ATP signals. Decrease of PPc signal intensity is due to chain length reduction and reduction in number of PPn molecules. Smaller decrease of ?-ATP compared to ?-ATP signal intensity can be attributed to maintenance of ATP concentration at the expense of PPn hydrolysis. Sensitivity to anoxia varies with the growth stage. It is greatest in 32-h and 44-h mycelium, in which PPn is used as an additional energy source, while the smallest effect was noted for 36-h fungi.

Regulation of phosphate acquisition in Saccharomyces cerevisiae

Membrane transport systems active in cellular inorganic phosphate (P(i)) acquisition play a key role in maintaining cellular P(i) homeostasis, independent of whether the cell is a unicellular microorganism or is contained in the tissue of a higher eukaryotic organism. Since unicellular eukaryotes such as yeast interact directly with the nutritious environment, regulation of P(i) transport is maintained solely by transduction of nutrient signals across the plasma membrane. The individual yeast cell thus recognizes nutrients that can act as both signals and sustenance. The present review provides an overview of P(i) acquisition via the plasma membrane P(i) transporters of Saccharomyces cerevisiae and the regulation of internal P(i) stores under the prevailing P(i) status.

Device for aeration and mixing of cell and organelle suspensions during NMR experiments

A device for aeration and mixing of cell or organelle suspensions in a vertical bore NMR magnet is described. Multiple external sensors (e.g., ion-selective electrodes) may be immersed in the suspension within the bore of the magnet. The sensors are positioned to avoid noise due to contact with gas bubbles and proximity to the probe head. The required sample volume is minimised. The modular design of components permits the use of the device in magnets of various internal dimensions, or with probe heads of different sample tube diameter, by modification of the simpler components of the assembly.

New aspects of inorganic polyphosphate metabolism and function

The review analyzes the results of recent studies on the biochemistry of high-molecular inorganic poly-phosphates (PolyPs). The data obtained lead to the following main conclusions. PolyPs are polyfunctional compounds. The main role of PolyPs is their participation in the regulation of metabolism both at the genetic and metabolic levels. Among the functions of PolyPs known at present, the most important are the following: phosphate and energy storage; regulation of the levels of ATP and other nucleotide and nucleoside-containing coenzymes; participation in the regulation of homeostasis and storage of inorganic cations and other positively charged solutes in an osmotically inert form; participation in membrane transport processes mediated by poly-beta-Ca2+-hydroxybutyrate complexes; participation in the formation and functions of cell surface structures; control of gene activity; and regulation of activities of the enzymes and enzyme assemblies involved in the metabolism of nucleic acids and other acid biopolymers. However, the functions of PolyPs vary among organisms of different evolutionary levels. The metabolism and functions of PolyPs in each cellular compartment of procaryotes (cell wall, plasma membrane, cytosol) and eucaryotes (nuclei, vacuoles, mitochondria, plasma membrane, cell wall, mitochondria, cytosol) are unique. The synthesis and degradation of PolyPs in the organelles of eucaryotic cells are possibly mediated by different sets of enzymes. This is consistent with of the endosymbiotic hypothesis of eucaryotic cell origin. Some aspects of the biochemistry of high-molecular PolyPs are considered to be of great significance to the approach to biotechnological, ecological and medical problems.

Phosphate transport in yeast vacuoles

The vacuole of the yeast Saccharomyces cerevisiae is a major storage compartment for phosphate. We have measured phosphate transport across the vacuolar membrane. Isolated intact vacuoles take up large amounts of added [32P]phosphate by counterflow exchange with phosphate present in the vacuoles at the time of their isolation. The bidirectional phosphate transporter has an intrinsic dissociation constant for phosphate of 0.4 mM. Exchange mediated by this carrier is faster than unidirectional efflux of phosphate from the vacuoles. The transporter is highly selective for phosphate; of other anions tested, only arsenate is also a substrate. Transport is strongly pH-dependent with increasing activity at lower pH. Similar phosphate transport behavior was observed in right-side-out vacuolar membrane vesicles.

An alleged yeast polyphosphate kinase is actually diadenosine-5', 5"'-P1,P4-tetraphosphate alpha,beta-phosphorylase

Polyphosphates are a major constituent of the yeast Saccharomyces cerevisiae. A purification of the enzyme polyphosphate kinase (E.C. 2.7.4.1) from this organism has been reported (Felter, S., and Stahl, A.J.C. (1973) Biochimie (Paris) 55, 245-251). The assay for activity used in this purification was the production of 32P-labeled nucleotide, presumed to be ATP, in the presence of [32P]polyphosphate and ADP. We have found that this assay does not reflect the activity of a polyphosphate kinase but rather the combination of an exopolyphosphatase, releasing free [32P]phosphate from the added [32P]polyphosphate, and the ADP-[32P]phosphate exchange activity of the enzyme diadenosine 5',5"'-P1, P4-tetraphosphate alpha, beta-phosphorylase (Ap4A phosphorylase). We also present direct evidence for the formation of an enzyme-AMP intermediate in the actin of Ap4A phosphorylase.