Ultrastructure of erythrocytes and leucocytes of Priapulus caudatus (de Lamarck) (Priapulida)

The marine priapulid Priapulus caudatus has a voluminous body cavity filled with a blood-like fluid containing erythrocytes and leucocytes (amoebocytes). The hematocrit of animals weighing 0.5–14 gm was 2–10%. The erythrocytes contain a hemerythrin blood pigment. The structure of the coelomocytes was studied by light and electron microscopy. The erythrocytes are nucleated and contain marginal bands, vacuoles and occasionally crystals. The cytoplasm has few organelles. The leucocytes are amoeboid motile cells, the cytoplasm of which contains numerous organelles. The most conspicuous of these are oval particles, probably representing developmental stages of lysosomes. Most of these organelles contain tubules stretching from one pole to another. In the hind part of the animal, certain tissues, primarily the posterior warts contain large numbers of coelomocytes. The histological picture is complicated, showing some resemblance to the lymphoepithelial tissues of vertebrates.     

Regulation of Pea Mitochondrial Pyruvate Dehydrogenase Complex : Does Photorespiratory Ammonium Influence Mitochondrial Carbon Metabolism?

Inactivation of the pyruvate dehydrogenase complex catalyzed by pyruvate dehydrogenase kinase was studied using intact mitochondria purified from green leaf tissue of pea (Pisum sativum L.) and dialyzed mitochondrial extracts. Thiamine pyrophosphate was inhibitory in dialyzed extracts but not in intact mitochondria, except in the presence of high concentrations of Na⁺. NH₄⁺, at concentrations as low as 20 micromolar, markedly stimulated inactivation in dialyzed extracts. K⁺ in the range 1 to 10 millimolar also enhanced inactivation. In contrast, Na⁺ was without affect at lower concentrations but was inhibitory at 10 to 100 millimolar levels. The effect of NH₄⁺ is discussed in relation to a possible regulatory interaction between photorespiratory NH₄⁺ production and the entry of carbon into the tricarboxylic acid cycle by way of the pyruvate dehydrogenase complex.     

Analysis of a model for random competition

A random competition model is reformulated as an urn model and its behavior is analysed.     

Immunosuppressive activity of antamanide and some of its analogues

In connection with our discovery of a strong immunosuppressive activity of cyclolinopeptide A (CLA), we investigated immunosuppressive properties of antamanide and a number of its analogues, including symmetrical antamanide, and compared them with the activities of cyclosporin A and CLA. The peptides were investigated by using plaque forming cell (PFC), graft-versus-host (GvH), delayed type hypersensitivity (DTH), and autologous rosette formation cell (ARFC) tests. Antamanide and symmetrical antamanide exhibit an immunosuppressive activity lower than CLA. Linear antamanide fragments are also active. At higher concentrations of the latter peptides, toxic effects occur.     

Regeneration of transgenic plants of Prunus armeniaca containing the coat protein gene of Plum Pox Virus

Summary A system was developed which allows the transfer of foreign genes into apricot cultivars. We report the transformation and regeneration of Prunus armeniaca plants with Agrobacterium tumefaciens strain LBA 4404 containing various binary plasmids, pBinGUSint, carrying the marker gene ß-glucuronidase (GUS) and pBinPPVm, carrying the coat protein gene of Plum Pox Virus (PPV). The marker gene GUS was used for optical evaluation of the efficiency of the transformation system. The coat protein gene of PPV was used to introduce coat protein mediated resistance against one of the most important pathogens of stone fruit trees in Europe and the whole Mediterranean area. This is the first report of the successful integration of a viral coat protein gene into a fruit tree species, opening a new perspective on the control of the disease.Abbreviations GUS ß-glucuronidase - PPV Plum Pox Virus - BA 6-benzylaminopurine - NPTII neomycin phosphotransferase II - CP coat protein - CaMV Cauliflower Mosaic Virus - P35S 35S promoter - MS Murashige and Skoog - PCR polymerase chain reaction - P/C/I phenol/chloroform/isoamylalcohol - RNase ribonuclease - dNTP deoxyribonucleosidetriphosphate - DMSO dimethyl sulfoxide     

1-Methyl-4-phenylpyridine (MPP+) induces oxidative stress in the rodent

MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) produces an irreversible parkinsonism in primates. Recent evidence suggests metabolism of MPTP to 1-methyl-4-phenylpyridine (MPP+) is required for toxicity. We have proposed that MPP+ may play a central role in the toxicity of MPTP, but direct assessment of the effects of MPP+ in brain is difficult. Therefore, we have sought to define the mechanism of peripheral MPP+ toxicity in the rat and mouse. Systemically administered MPP+ produced its major pathology in the lung and was typified by perivascular edema. An increase in plasma glutathione disulfide concentrations also resulted, suggesting that MPP+ in analogy to paraquat produces oxidative stress. In addition, the lethality of MPP+ in the mouse was increased by dietary selenium deficiency. These results define in both pathological and chemical terms the potent systemic toxicity of MPP+ and suggest that MPP+, because of its high concentration in primate brain, has the potential to play an important role in the CNS toxicity of MPTP.     

A comparative study of the physiological properties of the inner ear in Doppler shift compensating bats (Rhinolophus rouxi andPteronotus parnellii)

Summary Cochlear microphonic (CM) and evoked neural (N-1) potentials were studied in two species of Doppler shift compensating bats with the aid of electrodes chronically implanted in the scala tympani. Potentials were recorded from animals fully recovered from the effects of anesthesia and surgery. InPteronotus p. parnellii andRhinolophus rouxi the CM amplitude showed a narrow band, high amplitude peak at a frequency about 200 Hz above the resting frequency of each species. InPteronotus the peak was 25–35 dB higher in amplitude than the general CM level below or above the frequency of the amplitude peak. InRhinolophus the amplitude peak was only a few dB above the general CM level but it was prominent because of a sharp null in a narrow band of frequencies just below the peak. The amplitude peak and the null were markedly affected by body temperature and anesthesia. InPteronotus high amplitude CM potentials were produced by resonance, and stimulated cochlear emissions were prominent inPteronotus but they were not observed inRhinolophus. InPteronotus the resonance was indicated by a CM afterpotential that occurred after brief tone pulses. The resonance was not affected by the addition of a terminal FM to the stimulus and when the ear was stimulated with broadband noise it resulted in a continual state of resonance. Rapid, 180 degree phase shifts in the CM were observed when the stimulus frequency swept through the frequency of the CM amplitude peak inPteronotus and the frequency of the CM null inRhinolophus. These data indicate marked differences in the physiological properties of the cochlea and in the mechanisms responsible for sharp tuning in these two species of bats.     

Phosphorylation of Soybean (Glycine max L.) Nodule Phosphoenolpyruvate Carboxylase in Vitro Decreases Sensitivity to Inhibition by L-Malate

Phosphoenolpyruvate carboxylase (PEPC) from soybean (Glycine max L.Merr.) nodules was purified 187-fold to a final specific activity of 56 units mg-1 of protein. Sodium dodecyl sulfate (SDS) polyacrylamide gel electrophoresis (PAGE) revealed one major polypeptide band, with a molecular mass of 110 kD, after the final purification step. Two-dimensional PAGE resolved four isoelectric forms of the purified enzyme. Antibodies raised against the purified enzyme immunoprecipitated PEPC activity from a desalted nodule extract. Two cross-reacting bands were obtained when protein immunoblots of crude nodule extracts subjected to SDS-PAGE were probed with the antiserum. One of these corresponded to the 110-kD subunit of PEPC, and the other had a molecular mass of about 60 kD. PEPC was shown to be activated in a time-dependent manner when desalted soybean nodule extracts were preincubated with Mg.ATP in vitro. Activation was observed when PEPC was assayed at pH 7 in the absence of glycerol but not at pH 8 in the presence of glycerol. When o.5 mM L-malate was included in the assay, activation was much more pronounced than without malate. Maximal activation was 30% in the absence of L-malate and 200% in its presence. The L-malate concentrations producing 50% inhibition of PEPC activity were o.35 and 1.24 mM, respectively, before and after preincubation with Mg.ATP. The antiserum against soybean nodule PEPC was used to immunoprecipitate PEPC from a desalted nodule extract that had been preincubated with Mg.[[gamma]-32P]ATP. The immunoprecipitate was then subjected to SDS-PAGE, followed by autoradiography. The autoradiograph revealed intense labeling of the 110-kD subunit of PEPC following preincubation with [[gamma]-32P]ATP. The data suggest that soybean nodule PEPC becomes phosphorylated by an endogenous protein kinase, resulting in decreased sensitivity of the enzyme to inhibition by L-malate in vitro. The results are discussed in relation to the proposed functions of PEPC in legume nodules.     

A model for the regulation of D-3-phosphoglycerate dehydrogenase,a Vmax-type allosteric enzyme.

Escherichia coli D-3-phosphoglycerate dehydrogenase (ePGDH) is a tetramer of identical subunits that is allosterically inhibited by L-serine, the end product of its metabolic pathway. Because serine binding affects the velocity of the reaction and not the binding of substrate or cofactor, the enzyme is classified as of the Vmax type. Inhibition by a variety of amino acids and analogues of L-serine indicate that all three functional groups of serine are required for optimal interaction. Removing or altering any one functional group results in an increase in inhibitory concentration from micromolar to millimolar, and removal or alteration of any two functional groups removes all inhibitory ability. Kinetic studies indicate at least two serine-binding sites, but the crystal structure solved in the presence of bound serine and direct serine-binding studies show that there are a total of four serine-binding sites on the enzyme. However, approximately 85% inhibition is attained when only two sites are occupied. The three-dimensional structure of ePGDH shows that the serine-binding sites reside at the interface between regulatory domains of adjacent subunits. Two serine molecules bind at each of the two regulatory domain interfaces in the enzyme. When all four of the serines are bound, 100% inhibition of activity is seen. However, because the domain contacts are symmetrical, the binding of only one serine at each interface is sufficient to produce approximately 85% inhibition. The tethering of the regulatory domains to each other through multiple hydrogen bonds from serine to each subunit apparently prevents the body of these domains from undergoing the reorientation that must accompany a catalytic cycle. It is suggested that part of the conformational change may involve a hinge formed in the vicinity of the union of two antiparallel beta-sheets in the regulatory domains. The tethering function of serine, in turn, appears to prevent the substrate-binding domain from closing the cleft between it and the nucleotide-binding domain, which may be necessary to form a productive hydrophobic environment for hydride transfer. Thus, the structure provides a plausible model that is consistent with the binding and inhibition data and that suggests that catalysis and inhibition in this rare Vmax-type allosteric enzyme is based on the movement of rigid domains about flexible hinges.