Inhibitory effect of oxygen accumulation on the growth of Spirulina platensis

Summary The growth of Spirulina platensis was studied in a light-limited culture under various dissolved oxygen (DO) concentrations. At high DO concentration, e.g. at 1.25 mM DO, the growth rate was decreased up to 36 % compared with that of 0.063 mM DO. The retarded growth rate at high DO concentrations seemed to be coupled with the degeneration of photosynthetic activity in terms of O₂ evolution. Under higher DO concentrations, superoxide dismutase and ascorbate peroxidase activities tended to increase, while the contents of photosynthetic pigment, such phycocyanin, carotenoid and chlorophyll-a decreased distinctly.     

C1 proteins: a class of high-mobility-group non-histone chromosomal proteins from the fruit fly Ceratitis capitata

1. CM-cellulose chromatography of a fraction soluble in 5% perchloric acid from Ceratitis capitata chromatin yields three proteins, C1a1, C1a2 and C1b, which have been purified to electrophoretical homogeneity. 2. C1a1, C1a2 and C1b analyse like high mobility group (HMG) non-histone chromosomal proteins, although they do not exactly correspond with those from vertebrates. It is proposed that C1 proteins, as well as Drosophila D1 [Rodríguez Alfageme et al. (1980) Chromosoma, 78, 1-31] are representative of a class of insect-specific HMG proteins. Tryptic fingerprints show that C1a1 and C1a2 are very similar, but C1b is a somewhat distinct protein. Circular dichroism studies have shown that these preparations do not appreciably fold on increasing ionic strength. 3. The interactions between DNA and C1 proteins have been studied. These proteins precipitate DNA in 0.15 M NaCl, 0.015 M sodium citrate and the precipitation curves are cooperative. Soluble complexes between C1 proteins and DNA could be prepared in low ionic strength media and their thermal denaturation profiles obtained. C1 proteins do not destabilize DNA under the conditions used to prepare the complexes but the three proteins stabilize DNA to a different degree. From these studies it has been concluded that the association constant of C1b to DNA is smaller than that of C1a1 and C1a2.     

The courtship and mating of the Iberian midwife toad Alytes cisternasii (Amphibia: Anura: Discoglossidae)

Sexual encounters were staged in the laboratory among hormonally-primed Iberian midwife toads, Alytes cisternasii . In this species, pairing and fertilization are terrestrial. The male cares for the developing embryos on land, carrying them twined around his hind limbs until they hatch into tadpoles which he releases into water; his investment in the offspring then ends. The courtship of A. cisternasii can be divided into a pre- and post-ovulatory phase. An encounter is initiated when the female approaches the male and is clasped by him in inguinal amplexus. Both the male and the female produce vocalizations during the period prior to the initiation of amplexus. During amplexus, only the female vocalizes, changing her call to one that is of lower intensity, longer duration and more regularly emitted than before. During inguinal amplexus, the male engages in bouts of intense pedalling and gentle rocking behaviour, each bout being initiated when the female repositions herself beneath him. Rocking and pedalling cease when the female ovulates, at which time she exhibits a posture that we call Unkenkrampf. Ovulation occurs at this time, and is followed by sperm release by the male (seen as a series of lateral compressions of his body). After sperm release, the male moves forwards to engage the female in cervical amplexus and then manoeuvres his hind limbs such that the egg string becomes tangled around his ankles. The female may exhibit additional episodes of Unkenkrampf during this period, but these are not accompanied by further egg release. Episodes of Unkenkrampf (without ovulation) also may occur after the male dismounts from the female. Similar behaviour patterns to those observed in the laboratory are seen in natural populations of A. cisternasii . We compare and contrast our observations of A. cisternasii with those of other authors for this species and also for the common midwife toad, A. obstericans .     

Reaction of compound III of myeloperoxidase with ascorbic acid

A relatively pure and stable compound III of bovine spleen myeloperoxidase was prepared from native enzyme using the aerobic oxidation of dihydroxyfumarate to generate O2-(.). Spectral scans show well defined peaks at 450 and 625 nm and an isosbestic point between compound III and native enzyme at 440 nm. Compound III decayed to native enzyme without any detectable intermediate. The rate of decay was faster at alkaline pH values and also in the presence of superoxide dismutase. Ascorbic acid reduces compound III to native enzyme with a second order rate constant of (4.0 +/- 0.1) x 10(2) M-1 s-1. The ascorbic acid reduction of compound III has potential physiological relevance since it could help maintain the catalytic cycle of myeloperoxidase to generate the bactericidal agent hypochlorous acid.     

Reaction of autoxidation products of penicillamine with myeloperoxidase

Spectral evidence is presented which shows that penicillamine is able to initiate the formation of the oxidized intermediates of myeloperoxidase in the absence of exogenous hydrogen peroxide. The autoxidation of penicillamine presumably produces superoxide which dismutates spontaneously to form hydrogen peroxide. Thus, the formation of both compounds II and III of myeloperoxidase was observed. We also report that penicillamine can directly reduce cytochrome c and therefore, it could possibly act as a one-electron donor to myeloperoxidase.     

Structure of human nicotinamide/nicotinic acid mononucleotide adenylyltransferase. Basis for the dual substrate specificity and activation of the oncolytic agent tiazofurin.

Nicotinamide/nicotinate mononucleotide (NMN/ NaMN)adenylyltransferase (NMNAT) is an indispensable enzyme in the biosynthesis of NAD(+) and NADP(+). Human NMNAT displays unique dual substrate specificity toward both NMN and NaMN, thus flexible in participating in both de novo and salvage pathways of NAD synthesis. Human NMNAT also catalyzes the rate-limiting step of the metabolic conversion of the anticancer agent tiazofurin to its active form tiazofurin adenine dinucleotide (TAD). The tiazofurin resistance is mainly associated with the low NMNAT activity in the cell. We have solved the crystal structures of human NMNAT in complex with NAD, deamido-NAD, and a non-hydrolyzable TAD analogue beta-CH(2)-TAD. These complex structures delineate the broad substrate specificity of the enzyme toward both NMN and NaMN and reveal the structural mechanism for adenylation of tiazofurin nucleotide. The crystal structure of human NMNAT also shows that it forms a barrel-like hexamer with the predicted nuclear localization signal sequence located on the outside surface of the barrel, supporting its functional role of interacting with the nuclear transporting proteins. The results from the analytical ultracentrifugation studies are consistent with the formation of a hexamer in solution under certain conditions.     

Ethanol production from eucalyptus wood hemicellulose hydrolysate by Pichia stipitis

Ethanol production was evaluated from eucalyptus wood hemicellulose acid hydrolysate using Pichia stipitis NRRL Y-7124. An initial lag phase characterized by flocculation and viability loss of the yeast inoculated was observed. Subsequently, cell regrowth occurred with sequential consumption of sugars and production of ethanol. Polyol formation was detected. Acetic acid present in the hydrolysate was an important inhibitor of the fermentation, reducing the rate and the yield. Its toxic effect was due essentially to its undissociated form. The fermentation was more effective at an oxygen transfer rate between 1.2 and 2.4 mmol/L h and an initial pH of 6.5. The hydrolysate used in the experiences had the following composition (expressed in grams per liter): xylose 30, arabinose 2.8, glucose 1.5, galactose 3.7, mannose 1.0, cellobiose 0.5, acetic acid 10, glucuronic acid 1.5, and galacturonic acid 1.0. The best values obtained were maximum ethanol concentration 12.6 g/L, fermentation time 75 h, fermentable sugar consumption 99% ethanol yield 0.35 g/g sugars consumed, and volumetric ethanol productivity 4 g/L day. (c) 1992 John Wiley & Sons, Inc.