Light-activated heterotrophic growth of the cyanobacterium Synechocystis sp. strain PCC 6803: a blue-light-requiring process.

A glucose-tolerant strain of Synechocystis sp. strain 6803 will not grow on glucose under complete darkness unless given a daily pulse of white light, typically 5 min of 40 mumol m-2 s-1 (light-pulsed conditions). The light pulse is insufficient for photoautotrophy, as glucose is required and growth yield is dependent on glucose concentration. Growth rate is independent of fluence, but growth yield is dependent on fluence, saturating at 40 to 75 mumol m-2 s-1. A Synechocystis strain 6803 psbA mutant strain grows under light-pulsed conditions at rates similar to those for the glucose-tolerant strain, indicating that photosystem II is not required for growth. The relative spectral sensitivity of the growth of light-pulsed cultures (growth only in blue light, 400 to 500 nm, maximum at 450 nm) precludes energetic contribution from cyclic electron transport around photosystem I. Pulses of long-wavelength light (i.e., 550 and 650 nm) did not support the growth of Synechocystis strain 6803 and, when supplied before or after a blue-light pulse, did not inhibit blue-light-stimulated growth of Synechocystis strain 6803. We conclude that the required blue-light pulse does not support growth via photosynthetic electron transport but appears instead to function as an environmental signal regulating heterotrophic metabolism, cell division, or other photomorphogenic processes. We have termed the growth of Synechocystis strain 6803 pulsed with light and kept otherwise in complete darkness light-activated heterotrophic growth. This observation of a blue-light requirement for the growth of Synechocystis strain 6803 represents a novel blue light effect on the growth of a cyanobacterium.     

NAD-Linked Isocitrate Dehydrogenase: Isolation, Purification, and Characterization of the Protein from Pea Mitochondria

The NAD⁺-dependent isocitrate dehydrogenase from etiolated pea (Pisum sativum L.) mitochondria was purified more than 200-fold by dye-ligand binding on Matrix Gel Blue A and gel filtration on Superose 6. The enzyme was stabilized during purification by the inclusion of 20% glycerol. In crude matrix extracts, the enzyme activity eluted from Superose 6 with apparent molecular masses of 1400 ± 200, 690 ± 90, and 300 ± 50 kD. During subsequent purification steps the larger molecular mass species disappeared and an additional peak at 94 ± 16 kD was evident. The monomer for the enzyme was tentatively identified at 47 kD by sodium dodecyl-polyacrylamide gel electrophoresis. The NADP⁺-specific isocitrate dehydrogenase activity from mitochondria eluted from Superose 6 at 80 ± 10 kD. About half of the NAD⁺ and NADP⁺-specific enzymes remained bound to the mitochondrial membranes and was not removed by washing. The NAD⁺-dependent isocitrate dehydrogenase showed sigmodial kinetics in response to isocitrate (S_0.5 = 0.3 mm). When the enzyme was aged at 4°C or frozen, the isocitrate response showed less allosterism, but this was partially reversed by the addition of citrate to the reaction medium. The NAD⁺ isocitrate dehydrogenase showed standard Michaelis-Menten kinetics toward NAD⁺ (K_m = 0.2 mm). NADH was a competitive inhibitor (K_i = 0.2 mm) and, unexpectedly, NADPH was a noncompetitive inhibitor (K_i = 0.3 mm). The regulation by NADPH may provide a mechanism for coordination of pyridine nucleotide pools in the mitochondria.     

Isolation and characterization of the tricarboxylate transporter from pea mitochondria

The tricarboxylate transporter was solubilized from pea (Pisum sativum) mitochondria with Triton X-114, partially purified over a hydroxylapatite column, and reconstituted in phospholipid vesicles. The proteoliposomes exchanged external [¹⁴C]citrate for internal citrate or malate but not for preloaded d,l-isocitrate. Similarly, although external malate, succinate, and citrate competed with [¹⁴C]citrate in the exchange reaction, d,l-isocitrate and phosphoenolpyruvate did not. This tricarboxylate transporter differed from the equivalent activity from animal tissues in that it did not transport isocitrate and phosphoenolpyruvate. In addition, tricarboxylate transport in isolated plant mitochondria, as well as that measured with the partially purified and reconstituted transporter, was less active than the transporter isolated from animal tissues.     

Enhancement of protein precipitate strength and density by low-frequency conditioning

The use of a continuous, low-frequency conditioning process to alter the structure of protein precipitate aggregates is examined. An increase in the density of aggregates is correlated with the levels of fluid acceleration and hence hydrodynamic stress to which the aggregates are exposed during conditioning. A combination of low-frequency conditioning followed by shear break-up (as in the feed zone to a high-speed disk-stack centrifuge) is shown to result in a precipitate suspension of increased particle size at the fine end of the distribution, and having a greater sedimentation velocity. The resistance of large aggregates to shear disruption is increased by low-frequency conditioning.List of Symbols CR conditioning ratio - CRS conditioning ratio after shearing - d m amplitude of displacement - D m particle size - D _c m critical size for centrifuge recovery - f s^–1 frequency of vibration - G s^–1 mean velocity gradient - Q m³/s volumetric throughput - SR shear ratio - t s ageing time Greek Symbols s^–1 mass-average shear rate - K sedimentation shape factor - _a kg/m³ aggregate density - _f kg/m³ fluid density - _s kg/m³ solids density - kg/m³ aggregate-suspension density difference - Ns/m² kinematic viscosity - amplitude of pulse ratio (ref. 23, 9) - s mean residence time - _s solids volume fraction     

Assignment of the backbone 1H and 15N NMR resonances of bacteriophage T4 lysozyme

The proton and nitrogen (15NH-H alpha-H beta) resonances of bacteriophage T4 lysozyme were assigned by 15N-aided 1H NMR. The assignments were directed from the backbone amide 1H-15N nuclei, with the heteronuclear single-multiple-quantum coherence (HSMQC) spectrum of uniformly 15N enriched protein serving as the master template for this work. The main-chain amide 1H-15N resonances and H alpha resonances were resolved and classified into 18 amino acid types by using HMQC and 15N-edited COSY measurements, respectively, of T4 lysozymes selectively enriched with one or more of alpha-15N-labeled Ala, Arg, Asn, Asp, Gly, Gln, Glu, Ile, Leu, Lys, Met, Phe, Ser, Thr, Trp, Tyr, or Val. The heteronuclear spectra were complemented by proton DQF-COSY and TOCSY spectra of unlabeled protein in H2O and D2O buffers, from which the H beta resonances of many residues were identified. The NOE cross peaks to almost every amide proton were resolved in 15N-edited NOESY spectra of the selectively 15N enriched protein samples. Residue specific assignments were determined by using NOE connectivities between protons in the 15NH-H alpha-H beta spin systems of known amino acid type. Additional assignments of the aromatic proton resonances were obtained from 1H NMR spectra of unlabeled and selectively deuterated protein samples. The secondary structure of T4 lysozyme indicated from a qualitative analysis of the NOESY data is consistent with the crystallographic model of the protein.     

Historical and Life History Factors in the Biogeography of Mayflies

SYNOPSIS. Cladistic analysis of mayflies suggests that dispersalwas very asymmetrical after the new land connection betweenNorth and South America. Twenty-one genera apparently movedfrom South to North and Central America, but there is good evidencefor only one North American genus moving into the south. Testablepredictions are possible once the boreal (Laurasian) or austral(Gondwanian) designations are made. For example, Paracloeodes,a genus of austral origin, was predicted to be found in SouthAmerica, and in North America in warm rivers north and eastof its known distribution. These predictions have been confirmed.Other characteristics of tropical mayflies, such as length oflarval period and emergence and mating patterns, may be usedto predict habitats and characteristics of present North Americangenera. Merger events and consequent dispersal of organismshave profound influences on distributional patterns, and fromsuch information, biologically useful generalities can be made.     

Autonomic nervous control of gastric somatostatin secretion from the perfused rat stomach

The effect of parasympathetic and sympathetic nerve stimulation on the secretion of gastric somatostatin and gastrin has been studied in an isolated perfused rat stomach preparation. Stimulation of the vagus nerve inhibited somatostatin secretion and increased gastrin release. Splanchnic nerve stimulation increased somatostatin release during simultaneous atropine perfusion, but not in its absence, whereas gastrin secretion was unchanged. The secretory activity of the gastric D-cell was therefore reciprocally influenced by the sympathetic and parasympathetic nerves but sympathetic stimulation was only effective during muscarinic blockade.