Late pleistocene paleoclimates of the South Pacific based on statistical analysis of planktonic foraminifers

Statistical analysis applied to foraminiferal data from 78 South Pacific core tops enables the derivation of a transfer function that relates sea surface temperature to foraminiferal assemblages. Application of this transfer function to eight cores from the southern part of the East Pacific Rise yields estimates of the sea surface temperatures of the last glacial maximum, as well as the paleotemperature record of the past 150,000 years. Comparison of the last glacial temperature estimates with the recent sea surface temperature shows that the greatest change between glacial and present conditions (about 5°C) occurs in a climatically sensitive area near 50°S. Stratigraphic correlation of two cores from this area suggests that the last glacial started in this area with rapid cooling, and that the climate stayed generally cold until the end of the glacial. Similar general shape of the climatic record is found in the high latitudes of the North Atlantic as well as in the ice sheets of Greenland and Antarctica. In contrast to the similarity in the shape of these high-latitude records, they differ distinctly from the foraminiferal oxygen isotope record of several deep-sea cores which indicates a general gradual increase of ice volume from the beginning of the last glacial to the maximum glaciation which occurred about 18,000 years B.P.In the study area the rate of sediment accumulation during the last glacial is about two to three times less than in the last interglacial. There is no indication of increased carbonate solution during the glacial, and it is suggested that the change in the accumulation rate results from a reduction in the supply of calcareous shells to the sediment. It seems that with cooling, the environment becomes less favorable to organisms producing calcium carbonate tests, and therefore carbonate production decreases during the glacial.     

Electron spin resonance and photoreaction of Mn(II) in lettuce chloroplasts.

Electron spin resonance (esr) of lettuce chloroplasts yields three types of signals: (i) a broad (~900 G) signal around g = 2.22 (apparently due to Cu²⁺ complexes); (ii) an Mn²⁺ spectrum around g = 2.003 consisting of six hyperfine lines (A = 94.5 G) of ~30 G width; and (iii) a sharp signal at g = 2.00 due to photosignals I and II. The present work is concerned with the Mn²⁺ signal and its relation to the photosynthetic process. Intensity measurements were performed by comparing the intensities of the Mn²⁺ signals of two identical chloroplast preparations, one of which was slightly acidified. The integrated intensity of the signal in the normal preparation was approximately one-fourth of that in the acidified sample, suggesting that only the?$\text{1}\text{2}\text{?}\text{1}\text{2}$ fine structure band is observed in untreated chloroplasts. This indicates that the manganese in the chloroplasts is bound in an asymmetric environment, apparently in protein complexes. The Mn²⁺ signal is light sensitive, decreasing on illumination and reappearing in the dark. Typical values for the half-lives of the light and dark processes in normal chloroplasts are 0.25 and 2.1s, respectively. The effect is interpreted in terms of the photooxidation of Mn²⁺ to higher oxidation states which are invisible to esr spectroscopy. In order to determine whether this process is related to photosynthesis the effect of certain reagents and treatments that are known to affect the photosynthetic system was studied. It was found that the oxygen evolution inhibitors 3-(3,4 dichlorophenyl)-1,1-dimethylurea (DCMU) and carbonylcyanide-p-trifluoromethoxyphenylhydrazone (FCCP) as well as the electron donors, phenylenediamine and sodium ascorbate, reduce or completely eliminate the light effect on the Mn²⁺ signal. Heat treatment and Tris washing caused deceleration of both the light and dark reactions. These effects indicate that the photooxidation of the Mn²⁺ is related to the photosynthetic cycle, the most probable site being the water splitting apparatus of photosystem II.     

Growth and fermentation characteristics of new selected strains of Saccharomyces at high temperatures and high cell densities

Maintenance of high cell viability was the main characteristic of our new strains of thermotolerant Saccharomyces. Total sugar conversion to ethanol was observed for sugarcane juice fermentation at 38-40 degrees C in less than 10 h and without continuous aeration of the culture. Invertase activity differed among the selected strains and increased during fermentation but was not dependent on cell viability. Invertase activity of the cells and optimum temperature for growth, as well as velocity of ethanol formation, were dependent on medium composition and the type of strain used. At high sugarcane syrup concentrations, the best temperature for ethanol formation by strain 781 was 35 degrees C. Distinct differences among the velocities of ethanol production using selected strains were also observed in sugarcane syrup at 35-38 degrees C.     

Presynaptic Mechanism of Action of 4-Aminopyridine: Changes in Intracellular Free Ca2+ Concentration and Its Relationship to B-50 (GAP-43) Phosphorylation

Abstract: Recently we have shown that 4-aminopyridine (4-AP), a drug known to enhance transmitter release, stimulates the phosphorylation of the protein kinase C substrate B-50 (GAP-43) in rat brain synaptosomes and that this effect is dependent on the presence of extracellular Ca²⁺. Hence, we were interested in the relationship between changes induced by 4-AP in the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) and B-50 phosphorylation in synaptosomes. 4-AP (100 μ M ) elevates the [Ca²⁺]_i (as determined with fura-2) to approximately the same extent as depolarization with 30 m M K⁺ (from an initial resting level of 240 n M to ∼480 n M after treatment). However, the underlying mechanisms appear to be different: In the presence of 4-AP, depolarization with K⁺ still evoked an increase in [Ca²⁺]_i, which was additive to the elevation caused by 4-AP. Several Ca²⁺ channel antagonists (CdCl₂, LaCl₃, and diphenylhydantoin) inhibited the increase in B-50 phosphorylation by 4-AP. It is interesting that the increase in [Ca²⁺]_i and the increase in B-50 phosphorylation by 4-AP were attenuated by tetrodotoxin, a finding pointing to a possible involvement of Na⁺ channels in this action. These results suggest that 4-AP (indirectly) stimulates both Ca²⁺ influx and B-50 phosphorylation through voltage-dependent channels by a mechanism dependent on Na⁺ channel activity.     

Calcium binding induces conformational changes in muscle regulatory proteins.

Calcium binding to proteins containing the 'EF-hand' structural motif regulates a variety of biochemical processes including muscle contraction. Techniques such as protein crystallography, site-directed mutagenesis and domain transplantation experiments are being used to unravel the conformational changes induced by calcium binding.     

Enhancement of Endogenous Release of Glutamate and γ-Aminobutyric Acid from Hippocampus CA1 Slices After In Vivo Long-Term Potentiation

The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP.     

Molecular cloning of osteoma-inducing replication-competent murine leukemia viruses from the RFB osteoma virus stock.

We report the molecular cloning of two replication-competent osteoma-inducing murine leukemia viruses from the RFB osteoma virus stock (M. P. Finkel, C. A. Reilly, Jr., B. O. Biskis, and I. L. Greco, p. 353-366, in C. H. G. Price and F. G. M. Ross, ed., Bone--Certain Aspects of Neoplasia, 1973). Like the original RFB osteoma virus stock, viruses derived from the molecular RFB clones induced multiple osteomas in mice of the CBA/Ca strain. The cloned RFB viruses were indistinguishable by restriction enzyme analysis and by nucleotide sequence analysis of their long-terminal-repeat regions and showed close relatedness to the Akv murine leukemia virus.     

Water utilization of tropical hardwood hammocks of the Lower Florida Keys

Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.     

Comparative NMR studies on cardiac troponin C and a mutant incapable of binding calcium at site II

One- and two-dimensional NMR techniques were used to study both the influence of mutations on the structure of recombinant normal cardiac troponin C (cTnC3) and the conformational changes induced by Ca2+ binding to site II, the site responsible for triggering muscle contraction. Spin systems of the nine Phe and three Tyr residues were elucidated from DQF-COSY and NOESY spectra. Comparison of the pattern of NOE connectivities obtained from a NOESY spectrum of cTnC3 with a model of cTnC based on the crystal structure of skeletal TnC permitted sequence-specific assignment of all three Tyr residues, as well as Phe-101 and Phe-153. NOESY spectra and calcium titrations of cTnC3 monitoring the aromatic region of the 1H NMR spectrum permitted localization of six of the nine Phe residues to either the N- or C-terminal domain of cTnC3. Analysis of the downfield-shifted C alpha H resonances permitted sequence-specific assignment of those residues involved in the beta-strand structures which are part of the Ca(2+)-binding loops in both the N- and C-terminal domains of cTnC3. The short beta-strands in the N-terminal domain of cTnC3 were found to be present and in close proximity even in the absence of Ca2+ bound at site II. Using these assignments, we have examined the effects of mutating Asp-65 to Ala, CBM-IIA, a functionally inactive mutant which is incapable of binding Ca2+ at site II [Putkey, J.A., Sweeney, H. L., & Campbell, S. T. (1989) J. Biol. Chem. 264, 12370]. Comparison of the apo, Mg(2+)-, and Ca(2+)-bound forms of cTnC3 and CBM-IIA demonstrates that the inability of CBM-IIA to trigger muscle contraction is not due to global structural changes in the mutant protein but is a consequence of the inability of CBM-IIA to bind Ca2+ at site II. The pattern of NOEs between aromatic residues in the C-terminal domain is nearly identical in cTnC3 and CBM-IIA. Similar interresidue NOEs were also observed between Phe residues assigned to the N-terminal domain in the Ca(2+)-saturated forms of both cTnC3 and CBM-IIA. However, chemical shift changes were observed for the N-terminal Phe residues in CBM-IIA. This suggests that binding of Ca2+ to site II alters the chemical environment of the residues in the N-terminal hydrophobic cluster without disrupting the spatial relationship between the Phe residues located in helices A and D.