Regional Amino Acid Concentration in the Brains of Rats Exposed to High Pressures

Regional amino acid concentrations were measured in rat brain fixed by microwave irradiation at three levels of elevated atmospheric pressure corresponding to different phases of the high-pressure neurological syndrome [20 atmospheres absolute (ATA), no clinical signs; 60 ATA, tremor; 85 ATA, severe tremor and myoclonic jerks]. No changes in amino acid content occurred at 20 or 60 ATA. At 85 ATA glutamine content increased in hippocampus, striatum, cerebellum, and substantia nigra, and gamma-aminobutyric acid content increased in hippocampus. It is suggested that enhanced glutamate release in various subcortical structures contributes to the myoclonic activity observed at 85 ATA.     

Spectroscopic studies of the interactions of coenzymes and coenzyme fragments with pig heart, oxidized triphosphopyridine nucleotide specific isocitrate dehydrogenase

Spectroscopic, ultrafiltration, and kinetic studies have been used to characterize interactions of reduced and oxidized triphosphopyridine nucleotides (TPNH and TPN), 2'-phosphoadenosine 5'-diphosphoribose (Rib-P2-Ado-P), and adenosine 2',5'-bisphosphate [Ado(2',5')P2] with with TPN-specific isocitrate dehydrogenase. Close similarity of the UV difference spectra and of the protein fluorescence changes accompanying the formation of the binary complexes provides evidence for the binding of these nucleotides to the same site on the enzyme. From the pH dependence of the dissociation constants for TPNH binding to TPN-specific isocitrate dehydrogenase in the absence and in the presence of Mn2+, over the pH range 5.8-7.6, it has been demonstrated that the nucleotide binds to the enzyme in its unprotonated, metal-free form. The involvement of positively charged residues, protonated over the pH range studied, has been postulated. One TPNH binding site per enzyme subunit has been measured by fluorescence and difference absorption titrations. A dramatic effect of ionic strength on binding has been demonstrated: about a 1000-fold decrease in the dissociation constant for TPNH has been observed at pH 7.6 upon decreasing ionic strength from 0.336 (Kd = 1.2 +/- 0.2 microM) to 0.036 M (Kd = 0.4 +/- 0.1 nM) in the presence and in the absence of 100 mM Na2SO4, respectively. Weak competition of sulfate ions for the nucleotide binding site has been observed (KI = 57 +/- 3 mM). The binding of TPN in the presence of 100 mM Na2SO4 at pH 7.6 is about 100-fold weaker (Kd = 110 +/- 22 microM) than the binding of the reduced coenzyme and is similarly affected by ionic strength. These results demonstrate the importance of electrostatic interactions in the binding of the coenzyme to TPN-specific isocitrate dehydrogenase. The large enhancement of protein fluorescence caused by binding of TPN and Rib-P2-Ado-P (delta Fmax = 50%) and of Ado(2',5')P2 (delta Fmax = 41%) has been ascribed to a local conformational change of the enzyme. An apparent stoichiometry of 0.5 nucleotide binding site per peptide chain was determined for TPN, Rib-P2-Ado-P, and Ado(2',5')P2 from fluorescence titrations, in contrast to one binding site per enzyme subunit determined from UV difference spectral titration and ultrafiltration experiments. Thus, the binding of one molecule of the nucleotide per dimeric enzyme molecule is responsible for the total increase in protein fluorescence, while binding to the second subunit does not cause further change.(ABSTRACT TRUNCATED AT 400 WORDS)     

Meiotic maturation in Xenopus oocytes: a link between the cessation of protein secretion and the polarized disappearance of Golgi apparati

We have studied the relationship between the timing of the late meiotic events that occur during progesterone-induced oocyte maturation, and intracellular protein transport. We have monitored the secretion of chick oviduct proteins from Xenopus laevis oocytes microinjected with polyadenylated mRNA and found that chick ovalbumin and lysozyme are not secreted during the second meiotic metaphase, in contrast to the earlier prophase stage. Maturation had no detectable effect on the glycosylation of ovalbumin, whereas it affected the glycosylation of chick ovomucoid. As maturation proceeded, the Golgi apparati disappeared in a polarized fashion, beginning in the vegetal half. This disappearance coincided temporally and spatially with that of the nuclear envelope. We speculate that Golgi apparatus disappearance and the block in secretion are causally related.     

Effect of External pH on the Internal pH of Chlorella saccharophila

The overall internal pH of the acid-tolerant green alga, Chlorella saccharophila, was determined in the light and in the dark by the distribution of 5,5-dimethyl-2-[¹⁴C]oxazolidine-2,4-dione ([¹⁴C]DMO) or [¹⁴C]benzoic acid ([¹⁴C]BA) between the cells and the surrounding medium. [¹⁴C]DMO was used at external pH of 5.0 to 7.5 while [¹⁴C]BA was used in the range pH 3.0 to pH 5.5. Neither compound was metabolized by the algal cells and intracellular binding was minimal. The internal pH of the algae obtained with the two compounds at external pH values of 5.0 and 5.5 were in good agreement. The internal pH of C. saccharophila remained relatively constant at pH 7.3 over the external pH range of pH 5.0 to 7.5. Below pH 5.0, however, there was a gradual decrease in the internal pH to 6.4 at an external pH of 3.0. The maintenance of a constant internal pH requires energy and the downward drift of internal pH with a drop in external pH may be a mechanism to conserve energy and allow growth at acid pH.     

Temporal dynamics of estuarine phytoplankton: A case study of San Francisco Bay

Detailed surveys throughout San Francisco Bay over an annual cycle (1980) show that seasonal variations of phytoplankton biomass, community composition, and productivity can differ markedly among estuarine habitat types. For example, in the river-dominated northern reach (Suisun Bay) phytoplankton seasonality is characterized by a prolonged summer bloom of netplanktonic diatoms that results from the accumulation of suspended particulates at the convergence of nontidal currents (i.e. where residence time is long). Here turbidity is persistently high such that phytoplankton growth and productivity are severely limited by light availability, the phytoplankton population turns over slowly, and biological processes appear to be less important mechanisms of temporal change than physical processes associated with freshwater inflow and turbulent mixing. The South Bay, in contrast, is a lagoon-type estuary less directly coupled to the influence of river discharge. Residence time is long (months) in this estuary, turbidity is lower and estimated rates of population growth are high (up to 1–2 doublings d^–1), but the rapid production of phytoplankton biomass is presumably balanced by grazing losses to benthic herbivores. Exceptions occur for brief intervals (days to weeks) during spring when the water column stratifies so that algae retained in the surface layer are uncoupled from benthic grazing, and phytoplankton blooms develop. The degree of stratification varies over the neap-spring tidal cycle, so the South Bay represents an estuary where (1) biological processes (growth, grazing) and a physical process (vertical mixing) interact to cause temporal variability of phytoplankton biomass, and (2) temporal variability is highly dynamic because of the short-term variability of tides. Other mechanisms of temporal variability in estuarine phytoplankton include: zooplankton grazing, exchanges of microalgae between the sediment and water column, and horizontal dispersion which transports phytoplankton from regions of high productivity (shallows) to regions of low productivity (deep channels).Multi-year records of phytoplankton biomass show that large deviations from the typical annual cycles observed in 1980 can occur, and that interannual variability is driven by variability of annual precipitation and river discharge. Here, too, the nature of this variability differs among estuary types. Blooms occur only in the northern reach when river discharge falls within a narrow range, and the summer biomass increase was absent during years of extreme drought (1977) or years of exceptionally high discharge (1982). In South Bay, however, there is a direct relationship between phytoplankton biomass and river discharge. As discharge increases so does the buoyancy input required for density stratification, and wet years are characterized by persistent and intense spring blooms.     

Cleavage of human high molecular weight kininogen by factor XIa in vitro. Effect on structure and function

We have recently demonstrated that human high molecular weight kininogen (HMWK) is a pro-cofactor that is cleaved by kallikrein to yield a two-chain cofactor (HMWKa) and the nanopeptide bradykinin. This proteolysis enhances its association with an activating surface, an event necessary for expression of its cofactor activity. We now report that factor XIa is capable of hydrolyzing HMWK and releasing bradykinin in a purified system as well as cleaving and inactivating HMWK in a plasma environment during the contact-activation process. The profile of proteolysis differs from that produced by kallikrein and by factor XIIa in that the first cleavage by factor XIa yields 75- and 45-kDa polypeptides, whereas both factor XIIa and kallikrein initially produce 65- and 56-kDa species. Further proteolysis by all three enzymes eventually produces similar heavy chains (Mr = 65,000) and light chains (Mr = 45,000). However, the amount of factor XIa generated in plasma during contact activation further degrades the light chain of HMWK, eventually destroying its coagulant activity. Furthermore, in a purified system, enhancement of the degradation of HMWK coagulant activity by factor XIa was achieved when kallikrein was included in the incubation mixture, suggesting that the preferred substrate for factor XIa is the active form of HMWK (HMWKa), and not the pro-cofactor. These data suggest that factor XIa has the potential to act as a regulator of contact-activated coagulation by virtue of its ability to destroy the cofactor function of HMWK after its generation by either kallikrein, factor XIIa, or to a lesser extent, factor XIa, itself.     

The disease resistance response in pea is associated with increased levels of specific mRNAs

A cDNA library was constructed using poly(A)⁺RNA fromPisum sativum which had been treated for 8 h with the fungusFusarium solani f. sp.phaseoli. Two thousand four hundred recombinant colonies were screened by differential colony hybridization using³²P-labelled cDNAs prepared from RNA extracted from either noninoculated or inoculated pea tissue. cDNA clones were then selected, which showed greater hybridization with cDNA prepared from pea RNA 8 h post-inoculation than with a cDNA probe from 0 h. Seven distinct hybridization classes were chosen for further study. Northern blot analyses of total cellular RNAs inoculated for 16 h with eitherF. solani phaseoli or water demonstrated that each cDNA clone selected represents an mRNA species which increases substantially in abundance during infection. Results of³H-uridine pulse-labelling experiments suggested that enhanced synthesis is at least partially responsible for the accumulation of the fungus-inducible mRNAs which hybridized with the clones.