Time linkages between pollination onsets of different taxa over an 11-year period in Perugia,Central Italy

Times of pollination of different taxa in the atmosphere of Perugia (Central Italy) over an 11-year period (1982–1992) were recorded and analysed by means of a 7-day volumetric Hirst-type pollen trap. For some taxa, the pollination period varied from year to year from a chronological and/or quantitative point of view. Several taxa showed a linkage in their starting dates of pollination. Knowledge of this kind of linkage allows us to build a forecasting model.     

Effect of temperature on the stability and activity of crystalline ox liver nuclear and mitochondrial glutamate dehydrogenases

A study on the response of the stability and activity of crystalline ox liver nuclear and mitochondrial glutamate dehydrogenases to temperature variations has been carried out. The thermodynamic properties of the heat inactivation process and of the reaction with the substrates glutamate and α-ketoglutarate have been investigated. The heat inactivation of nuclear glutamate dehydrogenase proceeds at a faster rate than that of the mitochondrial enzyme in the temperature range 40–51 °C; the enthalpy of activation of the inactivation process is higher and the entropy is almost double, compared to the values of mitochondrial glutamate dehydrogenase. The effect of temperature on the maximal velocity shows that, with both glutamate and α-ketoglutarate, the enthalpy of activation with nuclear glutamate dehydrogenase is double and the decrease in entropy almost half of the values of the mitochondrial enzyme. The variation of the apparent K_m with temperature shows a decrease of the affinity of both enzymes for glutamate, with no major difference in the thermodynamic properties of the reaction. With α-ketoglutarate, on the other hand, the affinity of nuclear glutamate dehydrogenase decreased, whereas that of the mitochondrial enzyme increased with temperature. The process is therefore exothermic with the former enzyme, endothermic with the latter; furthermore, it occurs with a decrease in enthropy with nuclear glutamate dehydrogenase, but with a large increase with the mitochondrial enzyme. The studies on the effect of temperature on the activity were carried out in the range 20–44 °C.     

Spectroscopic and binding studies of azide to type-2-copper-depleted ascorbate oxidase from zucchini

Summary Binding of azide to type-2-copper-depleted (T2D) zucchini ascorbate oxidase, containing reduced type-3 Cu centers, and met-T2D ascorbate oxidase, containing oxidized type-3 Cu centers, has been studied spectroscopically. In both cases titration with azide in 0.1 M phosphate pH 6.8 produces a broad near-ultraviolet band with maximum at 455 nm (e 2500 M^–1 cm^–1, with respect to the met-T2D enzyme) and shoulder at 390 nm (e 1700 M^–1 cm^–1), that are assigned to(azide)Cu(II) ligand-to-metal charge transfer (LMCT) transitions. This is accompanied by a reduction of absorbance at 330 nm in the met-T2D) enzyme adduct (e –1400 M^–1 cm^–1). A broad circular dichroic band of negative sign between 370–480 nm corresponds to the LMCT absorption band. Analysis of the titration data indicates that one azide ion binds independently to each of the binuclear T3 Cu couples with low affinity (K = 50 M^–1). The ESR signal of the T1 Cu observed in frozen solutions of the T2D enzyme is also perturbed by the addition of azide. The analogies in the azide-binding characteristics between ascorbate oxidase and laccase are discussed.     

Differential stimulation of pancreatic-polypeptide and gastrin secretion by bombesin in man

Bombesin, besides many other actions on the mammalian gastroentero-pancreatic tract, strongly stimulates the release of pancreatic-polypeptide (PP) in dogs. In 8 healthy human volunteers (5 males, 3 females), the PP response during bombesin infusion was low (25.7 ± 6.3 peak vs. 5.0 ± 2.0 basal pmol/1) compared to the effect of a protein meal (144.1 ± 13.4 pmol/1) or to the gastrin response to the same dose of the amphibian polypeptide (140.0 ± 23.6 pmol/1 eq SHG 17 I). The response pattern of PP and gastrin was different as PP concentrations peaked 10 min after cessation of bombesin infusion (32.0 ± 4.9 pmol/1) when gastrin concentrations already were down to one third of the maximal response. Atropine inhibited the PP response to bombesin but did not abolish it completely. It is concluded that in man, the total effect of bombesin on PP secretion is minor compared both to the effect of the peptide on gastrin secretion in man and to the effect of bombesin in dogs. It is suggested that bombesin might have a dual, inhibitory-stimulatory, effect on PP secretion in man.     

Synaptosomal phospholipid pool in rabbit brain and its effect on GABA uptake

Rabbit synaptosomes have been used to study the effect of the base-exchange reaction in membrane phospholipids on -aminobutyric acid (GABA) transport in vitro. The uptake of GABA was measured after a base-exchange reaction with ethanolamine, choline, orl-serine and after subsequent displacement of these exchanged moieties from lipid by bases of similar or different structures which were added to the synaptosomal medium. Serine incorporation stimulated GABA transport, but its displacement from membrane lipid by choline or ethanolamine induced an inhibition of GABA transport. Ethanolamine incorporation inhibited GABA transport, but its displacement by serine or choline resulted in stimulation of GABA uptake. Choline incorporation also inhibited GABA transport, although less than ethanolamine. The pool size of synaptosomal phospholipids, presumably involved in GABA uptake, accounted for 0.2 to 10% of the total content of membrane phospholipid. Thus, alteration of phospholipid compositior by exchange of the lipid hydrophilic head-groups influences the extent GABA uptake into rabbit synaptosomes.     

Stimulation of poly(dT) transcription by Bacillussubtilis RNA polymerase in the presence of adenosine monophosphate

The rate of synthesis of poly(A) on a ply(dT) template by $\text{Bacillus}\text{subtilis}$ RNA polymerase is a function of ATP concentration and is expressed as a sigmoidal curve. The addition of millimolar concentration of AMP to low concentrations of ATP stimulates synthesis of poly(A) twenty fold and raises the rate of synthesis to the levels obtained at high ATP concentrations. The reaction is completely dependent upon the presence of poly(dT) and requires the complementary mononucleotide. Stimulation of poly(A) synthesis by AMP is more evident with the holoenzyme. Analysis of poly(A) products by acrylamide gels showed that the poly(A) synthesized in the presence of AMP has an higher molecular weight than poly(A) synthesized in the absence of AMP.     

An inducible n-alkane hydroxylase system containing cytochrome “O” from Candida lipolytica

Summary In this work the terminal oxidase system of C. lipolytica grown on n-alkanes was identified, and partially purified. Spectral characteristics typical of cytochrome O are obtained, inhibition and photodissociation of CO are reported.     

Conformational properties of the N-terminal residues of S-peptide. I. The ribonuclease S′ system

The contribution of the 1–6 N-terminal sequence to the conformational properties of the S-peptide (the 1–20 sequence of ribonuclease A) was assessed by determining in the ribonuclease S′ system the helical content and the binding capability of synthetic [Orn¹⁰]-S-peptide analogs, in which lysine¹, glutamic² and threonine³ were progressively deleted, alanine⁴ and alanine⁵were alternatively replaced by serine, and alanine⁶ was substituted by serine or proline. Both the deletion of the three N-terminal residues and the alanine⁶/proline replacement produces the loss of the helical structure up to lysine⁷. No or minor effects are found in all other cases. From the comparison of the binding data, the energy for the conformational stabilization of the N-terminal region was calculated to amount to 1.4 kcal/mol. The results are discussed in comparison with the known x-ray data of the enzyme, with some predictive rules of secondary structure which were applied to this region and with the known phylogenetic variance of the residues in this region.