Adaptive phosphate uptake behaviour of phytoplankton to environmental phosphate fluctuations

When phytoplankton growth in lakes is limited by the available phosphate, the external phosphate concentration fluctuates around a threshold value at which available energy is insufficient to drive phosphate incorporation into a polyphosphate pool. As a result, occasional increases in the external concentration are experienced by phytoplankton as a series of phosphate pulses. Based on [(32) P] phosphate uptake experiments with lake phytoplankton, we show that a community is able to process information about the experienced pattern of phosphate pulses via a complex regulation of the kinetic and energetic properties of cellular phosphate uptake systems. As a result, physiological adaptation to alterations of ambient phosphate concentration depends on the pattern of phosphate fluctuations to which the community had been exposed during its previous growth. In this process, the entire community exhibits coherent uptake behaviour with respect to a common threshold value. Thereby, different threshold values result from different antecedent pulse patterns, apparently unrestrained by the amount of previously stored phosphate. The coherent behaviour observed contradicts the basic assumptions of the competitive exclusion principle and provides an alternative perspective for explaining the paradoxical coexistence of many phytoplankton species.     

Organic phosphate probes of the avian renal phosphate secretory mechanism

Parathyroid hormone (PTH) stimulates net renal inorganic phosphate (Pi) secretion in domestic fowl (Gallus domesticus). Recent evidence indicates that secreted Pi is derived from a highly sequestered, presumably organic, phosphate pool. A modified Sperber technique was used to survey the response of domestic fowl to unilateral renal portal infusions of organic phosphate compounds that had been implicated in previous studies of Pi secretion. None of the organic phosphate compounds produced a significant unilateral Pi secretory effect. It is concluded that these compounds neither directly stimulate Pi secretion in normal or parathyroidectomized birds, nor are they rate-limiting for the Pi secretory mechanism in birds infused with PTH.     

Effect of dietary phosphate on intestinal calcium and phosphate absorption

Intestinal Ca and P absorption was investigated on rachitic chicks raised on diets with a 1% Ca and 0.3% or 1% P contents. 45Ca and 32P absorption was determined by the technique of the isolated gut sac in vivo. In addition, 32P transport was also measured by the everted gut sac procedure in vitro. Treatment with vit. D3 during 7 days increased the 45Ca absorption in animals fed diets containing 0.3% or 1% P. 32P absorption showed an increase after 2 days of treatment and a decrease afterwards. The reduction of 32P absorption was larger in animals fed diet with 1% P. Study of 32P transport with the everted gut sac technique showed an increase after vit. D3 and a loss of intracellular P, regardless the duration of treatment.     

Dynamics of phosphate limited algal growth: Simulation of phosphate shocks

A simulation model is suggested which describes transient growth of the green alga Chlorella pyrenoidosa after exposure of phosphate limited chemostatic cultures to phosphate shocks. The specific growth rate is related to an internal concentration of functional phosphorus. The model includes a metabolic activity functional as suggested by Powell (1969), and it is assumed that phosphate taken up by the cells passes through an intermediate pool of not functional phosphorus which is thought to inhibit growth. Comparisons are made with a simpler model described previously.     

Mutagenesis of isopentenyl phosphate kinase to enhance geranyl phosphate kinase activity

Isopentenyl phosphate kinase (IPK) catalyzes the ATP-dependent phosphorylation of isopentenyl phosphate (IP) to form isopentenyl diphosphate (IPP) during biosynthesis of isoprenoid metabolites in Archaea. The structure of IPK from the archeaon Thermoplasma acidophilum (THA) was recently reported and guided the reconstruction of the IP binding site to accommodate the longer chain isoprenoid monophosphates geranyl phosphate (GP) and farnesyl phosphate (FP). We created four mutants of THA IPK with different combinations of alanine substitutions for Tyr70, Val73, Val130, and Ile140, amino acids with bulky side chains that limited the size of the side chain of the isoprenoid phosphate substrate that could be accommodated in the active site. The mutants had substantially increased GP kinase activity, with 20-200-fold increases in k(cat)(GP) and 30-130-fold increases in k(cat)(GP)/K(M)(GP) relative to those of wild-type THA IPK. The mutations also resulted in a 10(6)-fold decrease in k(cat)(IP)/K(M)(IP) compared to that of wild-type IPK. No significant change in the kinetic parameters for the cosubstrate ATP was observed, signifying that binding between the nucleotide binding site and the IP binding site was not cooperative. The shift in substrate selectivity from IP to GP, and to a lesser extent, FP, in the mutants could act as a starting point for the creation of more efficient GP or FP kinases whose products could be exploited for the chemoenzymatic synthesis of radiolabeled isoprenoid diphosphates.     

Inorganic phosphate determination in the presence of a labile organic phosphate: assay for carbamyl phosphate phosphatase activity

A periodate-resorcinol method for bound sialic acid using the Technicon Autoanalyzer II is presented. It has a sensitivity similar to the manual method, is linear between 5 and 65 nmol/ml, requires less than 0.2 ml of sample, and can be run at the rate of 70 samples/h. Little cross-reaction with common matrix and cell components was found. The method is compatible with many commonly used volatile and nonvolatile chromatographic buffers. The use of a bound sialic acid standard such as N-acetylneuraminyl lactose is recommended.     

The conversion of pyridoxine phosphate into pyridoxal phosphate in Escherichia coli

1. Evidence is presented for the presence of pyridoxine phosphate oxidase in aqueous extracts of Escherichia coli. Some comparison is made with pyridoxamine phosphate oxidase. 2. Isoniazid and iproniazid were found to combine with pyridoxal phosphate, but isoniazid did not combine with either pyridoxamine phosphate or pyridoxine phosphate. Both oxidase activities were somewhat inhibited by benzylamine and putrescine, but not by phenethylamine or cadaverine. 3. The significance of pyridoxine phosphate oxidase in cell metabolism is discussed.