Influence of temperature and nitrogen concentration on photosynthesis ofDunaliella viridis Teodoresco

The photosynthetic behaviour ofDunaliella viridis has been studied under a combination of three variables: irradiance (0–900 mol m^–2 s^–1), temperature (15, 23, 31, 38, 42 °C) and nitrogen concentration (0.05, 0.5, 1.5, 5, 10 mM NO ₃ ^- ) at a salinity of 2 M NaCl.The highest rates of photosynthesis have been found at 31 °C and a nitrate concentration of 10 mM. There exists a synergistic effect between temperature and nitrogen availability on the photosynthesis ofD. viridis; under nitrogen deficiency oxygen evolution is low, even null at high temperature. The interaction between these two variables of control occurs in a multiplicative way. There is also a general increase in photosynthetic pigments following the increase in nitrogen concentration in the culture medium. The normalization of net photosynthesis data in relation to chlorophylla shows that nitrogen concentration makes an indirect control of the photosynthetic rate ofD. viridis through the variation of pigment concentration.     

Quantitative autoradiographic localization of neuropeptide Y (NPY) binding sites in rat posterior pituitary lobe

1. We have localized and quantified neuropeptide Y (NPY) binding sites in the rat pituitary gland after incubation of tissue sections in the presence of 125I-Bolton-Hunter NPY followed by autoradiography, computerized microdensitometry, and comparison to 125I-standards. 2. In the rat, NPY binding sites are localized exclusively to the part of the posterior pituitary lobe closer to the pituitary stalk. No NPY binding sites could be found in the intermediate or the anterior pituitary lobes. 3. Our results suggest a role for NPY in the regulation of pituitary function and, in particular, that of the neural lobe.     

Mitogenic,immunoadjuvancy, and genetic studies on fatty acyl maltose

Summary Three synthetic glycolipids, maltose tetrapalmitate (MTP), maltose hexastearate (MHS), and maltose hexalinoleate (MHL) prepared as nontoxic lipid A analogs, and Escherichia coli lipopolysaccharide (LPS) were assayed for their mitogenic activity using spleen lymphocytes in nine inbred mouse strains and three F1 hybrids. The MTP and LPS were also assayed for their ability to enhance plaque-forming cell (PFC) responses using sheep red blood cells as the antigen in th same inbred mouse strains and F1 hybrids, The mitogenic activity of synthetic glycolipids was several fold lower than that of LPS and MHL was inferior to MTP and MHS. DBA/2J was the most responsive strain for MTP and DBA/1J and C3H/HeJ the least. The mitogenic activity of MTP was generally in agreement with the PFC response stimulation by it. Lowdose cyclophosphamide treatment of mice synergized MTP for PFC response augmentation. Genetic studies on MTP mitogenicity revealed that 90% of responder DBA/2J X nonresponder C3H/HeJ F1 hybrids had intermediate mitogenic activity. Among F2, 73% had intermediate-high activity and 27% were nonmitogenic. Among F1 X C3H/HeJ backcrosses 11% had high, 56% intermediate, and 33% had no mitogenic activity, whereas, for the F1 X DBA/2J backcross, 14% had high, 36% intermediate, and 50% low or negligible activity. The data favored a single gene for MTP activation of immune cells.This work was supported, in part, by a grant from the National Cancer Institute of Canada, and by grant from the Cancer Research Society Inc.     

An improved purification procedure and properties of casein kinase II from brain

A simple and short purification procedure applicable to casein kinase II has been developed, for fully characterizing the enzyme from calf cerebral cortex cytosol. The procedure consists of four chromatographic steps: DEAE-cellulose, phosphocellulose, phosvitin-Sepharose and ATP-agarose which yields 87% pure casein kinase II. The purified enzyme shows three major bands with apparent molecular masses of 42, 38, and 27 kDa by polyacrylamide gel electrophoresis in sodium dodecyl sulfate and is self-autophosphorylated on its 27 kDa polypeptide. The enzyme shows all the characteristics described for casein kinase II from other sources: it is independent of cyclic nucleotides, calcium/phospholipids, and double-stranded poly(I).poly(C); it can utilize both ATP and GTP as phosphoryl donors and can phosphorylate both casein and phosvitin but not histone. The kinetic studies establish that theK _m for ATP is 12.5 M and 25.1 M when using phosvitin and casein respectively as phosphoryl acceptors. TheK _m for phosvitin is 0.91 mg/ml and for casein 1.43 mg/ml, while theV _max is 315 nmol/min/per mg protein and 479 nmol/min/per mg protein for phosvitin and casein respectively. The activity of the kinase is highly stimulated by KCl or NaCl, and almost completely inhibited by heparin concentrations of 1 g/ml (92%). This inhibition is reduced to only 33% in the presence of optimal KCl concentrations (150 mM). Spermine stimulates enzyme activity, whilst hemin produces a slight inhibition.     

HLA-DQ system and insulin-dependent diabetes mellitus in Japanese: does it contribute to the development of IDDM as it does in Caucasians?

Fifty-six unrelated Japanese patients with insulin-dependent diabetes mellitus (IDDM) were HLA-typed, and restriction fragment length polymorphism (RFLP) analysis was performed after enzyme digestion with Bam HI and Taq I by using both DR and DQ probes. As previously reported, increased frequencies of Bw54, Cw1, DR4, and DRw53, which are in strong linkage disequilibrium in the Japanese population and make the characteristic Japanese haplotype, were confirmed. DQw4, a new allele of the DQ system recognized by the monoclonal antibody HU-46 and in linkage disequilibrium with this haplotype, presented the highest IDDM association. The RFLP analysis also showed the strongest correlation to IDDM when the DQ probe was applied. These results indicate that HLA-DQ might play the most important role in the development of IDDM in Japanese as well as in Caucasians. The correlation of DQ amino acid sequences strongly associated with IDDM in Japanese are discussed in this study, and contrasting results were found when such sequences were compared with those of Caucasians.Abbreviations used in this paper IDDM insulin-dependent diabetes mellitus - RFLP restriction fragment length polymorphism - Asp aspartic acid - Asp-57 aspartic acid at the 57th residue of the DQ chain - non-Asp-57 nonaspartic acid at the 57th residue of the DQ chain - R.R. relative risk of Woolf and Haldane     

Immobilization of enzymes on alumina by means of pyridoxal 5′-phosphate

A number of proteases have been immobilized on alumina in a two-step procedure: the first step converted them into semisynthetic phosphoproteins which, in the second step, spontaneously bonded to alumina through their phosphate function. The immobilized enzymes thus obtained showed the physical properties typical of the inorganic carrier and a high activity on low molecular weight substrates.     

Isolation and biochemical characterization of Streptomyces clavuligerus mutants in the biosynthesis of clavulanic acid and cephamycin C

Summary Seven mutants of Streptomyces clavuligerus blocked in the biosynthesis of clavulanic acid, cephamycin C, or both antibiotics, have been isolated and characterized. Mutants nca1 and nca2 were unable to synthesize clavulanic acid but produced cephamycin C. Mutants nce1 and nce2 were completely blocked in cephamycin C production but formed clavulanic acid. A third group (mutants ncc1, ncc4 and ncc5) failed to produce both antibiotics. Arginase activity (forming ornithine) was very low in mutants ncc1 and ncc5. All the mutants blocked in clavulanic acid biosynthesis showed a normal ornithine--aminotransferase activity. Mutant ncc1, blocked in cephamycin biosynthesis, lacked completely lysine--aminotransferase (forming -aminoadipic acid) and isopenicillin N synthase. Two other mutants (nce2 and nce5) lacked isopenicillin N synthase. There was a good correlation between the isopenicillin N synthase and the lysine--aminotransferase activities of the nca mutants and the ability of those strains to produce cephamycin C. The condensing enzyme involved in the formation of the clavulanic acid nucleus appears to be different from the isopenicillin N synthase.Dedicated to Professor H.-J. Rehm on the occasion of his 60th birthday     

Effects of phosphorylation, MgATP, and ionic strength on the rates of papain degradation of heavy and light chains of smooth muscle heavy meromyosin at the S1-S2 junction

The effects of ionic strength, MgATP, and phosphorylation on the degradation rates of heavy meromyosin (HMM) by papain have been compared to their effects on the sedimentation coefficient (s20,w) to determine the relationship of the degradation rate to the equilibrium between the flexed and the extended forms (Suzuki, H., Stafford, W. F., Slayter, H. S., and Seidel, J. C. (1985) J. Biol. Chem. 260, 14810-14817). At 0.025 M NaCl, where HMM is predominantly in the flexed form, MgATP, Mg-adenylyl imidodiphosphate or MgADP reduce kH by 80-90%. MgATP exerts its optimal effect at this ionic strength, where at least 70% of HMM is flexed in the presence or absence of MgATP, suggesting that nucleotides reduce kH by decreasing the proteolytic susceptibility of the flexed form. At 0.5 M NaCl, where HMM is in the extended form, MgATP has no effect on kH. At low ionic strengths phosphorylation decreases kH but increases it in the presence of MgATP. Plots of kH against s20,w determined at various ionic strengths are linear, the data for phosphorylated and dephosphorylated HMM falling on the same line. Thus, raising the ionic strength or phosphorylating the 20-kDa light chain appears to alter kH by increasing the fraction of HMM in the extended form. The degradation rate of the 20-kDa light chain (kL) of dephosphorylated HMM responds to changes in ionic strength in essentially the same way as does kH, suggesting that the response of kL to changes in ionic strength can also be attributed to conversion of HMM to the extended form. However, kL for phosphorylated HMM measured in the presence of MgATP exhibits very little dependence on ionic strength.     

Electrogenic behavior of the human red cell Ca2+ pump revealed by disulfonic stilbenes

Summary A systematic study was made of the action of 4-acetamido-4-isothiocyanostilbene-2,2-disulfonic acid (SITS) and 4,4-diisothiocyanostilbene-2,2-disulfonic acid (DIDS) on active Ca²⁺ transport of human erythrocytes. Pumping activity was estimated in inside-out vesicles (IOV's) by means of Ca²⁺-selective electrodes or use of tracer⁴⁵Ca²⁺. The stilbenes exhibited an approximately equal inhibitory potency and their action could be overcome by carbonyl cyanidep-trifluoromethoxyphenylhydrazone (FCCP) at low but not at high stilbene concentrations. In the absence of DIDS. Ca²⁺ transport was not affected upon addition of valinomycin, but it was appreciably reduced when vesicles were preincubated with low DIDS concentrations. Such an effect was strictly dependent on the external K⁺ concentration and it was abolished when valinomycin was added together with FCCP. Similar results were obtained using IOV's prepared from intact cells which had been previously exposed to the stilbene. The findings clearly demonstrate the presence in human red cells of a partially electrogenic Ca²⁺ pump, exchanging one Ca²⁺ ion for one proton.     

Phosphate sequestration by glycerol and its effects on photosynthetic carbon assimilation by leaves

Glycerol induced a limitation on photosynthetic carbon assimilation by phosphate when supplied to leaves of barley (Hordeum vulgare L.) and spinach (Spinacia oleracea L.). This limitation by phosphate was evidenced by (i) reversibility of the inhibition of photosynthesis by glycerol by feeding orthophosphate (ii) a decrease in light-saturated rates of photosynthesis and saturation at a lower irradiance, (iii) the promotion of oscillations in photosynthetic CO₂ assimilation and in chlorophyll fluorescence, (iv) decreases in the pools of hexose monophosphates and triose phosphates and increases in the ratio of glycerate-3-phosphate to triose phosphate, (v) decreased photochemical quenching of chlorophyll fluorescence, and increased non-photochemical quenching, specifically of the component which relaxed rapidly, indicating that thylakoid energisation had increased. In barley there was a massive accumulation of glycerol-3-phosphate and an increase in the period of the oscillations, but in spinach the accumulation of glycerol-3-phosphate was comparatively slight. The mechanism(s) by which glycerol feeding affects photosynthetic carbon assimilation are discussed in the light of these results.Abbreviations Chl chlorophyll - C _i intercellular concentration of CO₂ - P phosphate - PGA glycerate-3-phosphate - Pi orthophosphate - triose-P sum of glyceraldehyde-3-phosphate and dihydroxyacetone phosphate