Characterization of a light-dependent glutamate synthase activity in Chlamydomonas reinhardtii

Photosynthetically active vesicles prepared from Chlamydomonas reinhardtii retained a light-dependent glutamate synthase activity which was highly specific for 2-oxoglutarate (K_m=2.1 mM) and L-glutamine (K_m=0.9 mM) as amido group acceptor and donor respectively. This activity was inhibited by azaserine, p-hydroxymercuribenzoate and 3-(p-chlorophenyl)-1,1-dimethyl urea.Light-dependent synthesis of glutamate was also obtained by coupling Chlamydomonas photosynthetic particles to purified ferredoxin-glutamate synthase, using ascorbate and 2,6-dichlorophenol-indophenol as electron donor. This system was also specific for 2-oxoglutarate (K_m=1 mM) and L-glutamine (K_m=0.8 mM) as substrates, and was stimulated by dithioerythritol. Azaserine and p-hydroxymercuribenzoate, but not 3-(p-chlorophenyl)-1,1-dimethyl urea, inhibited the reconstituted activity; high concentrations of 2-oxoglutarate were inhibitory.Abbreviations A Absorbance - CCP p-Trichlorometoxi-carbonylcyanide-phenylhydrazone - Chl Chlorophyll - CMU 3-(p-Chlorophenyl)-1,1-dimethyl urea - DPIP 2,6-Dichlorophenol-indophenol - DTE Dithioerythritol - MSX L-Methionine, D-L, sulfoximine - MV Methyl viologen     

The biogeochemical cycle of the adsorbed template

Experimental results are presented for the verification of the first adsorption step of the ‘adsorbed template’ biogeochemical cycle, a simple model for a primitive prebiotic replication system. The adsorption of Poly-C, Poly-U, Poly-A, Poly-G, and 5′-AMP, 5′-GMP, 5′-CMP and 5′-UMP onto gypsum was studied. It was found that under the conditions of the experiment, the polymers have a very high affinity for the mineral surface, while the monomers adsorb much less efficiently.     

Purification of bovine liver histidyl-tRNA synthetase, the Jo-1 antigen of polymyositis: size of the whole enzyme and its characteristic proteolytic fragments

We have recently reported the marked increase in frequency which can be achieved in the detection of the anti-Jo-1 antibody of polymyositis in serum samples by replacing commercial mixtures of cytoplasmic and nuclear antigens with the purified antigen, histidyl-tRNA synthetase. The present paper describes a method for purifying this antigen and an investigation of its size. Molecular masses previously reported for the enzyme have varied from 85-154 kDa and subunit molecular masses varying from 40-77 kDa have been observed. Several of these fragments are of sizes similar to those of a number of other autoantigens commonly observed in connective tissue diseases. Since the clinical identification of these autoantigens often relies exclusively on size determination by Western blotting, we have characterized the commonly occurring fragments of histidyl-tRNA synthetase lest they confuse such identification. It is concluded that histidyl-tRNA synthetase, like many other aminoacyl-tRNA synthetases, is subject to severe proteolysis during extraction procedures. Several characteristic fragments (Mr = 80, 75, 61, 55, 50 and 45 kDa) result, a finding that provides a satisfactory explanation of the various values previously reported. The intact bovine enzyme is a dimer of molecular mass close to 160 kDa.     

Genetic study on indole-3-acetic acid production by ectomycorrhizal Hebeloma species: inter- and intraspecific variability in homo- and dikaryotic mycelia

Summary Interspecific variability of indole-3-acetic acid (IAA)-synthesizing activity was examined within 12 wild strains of different Hebeloma species. Interstrain variability was studied within 11 wild strains of Hebeloma cylindrosporum (Romagnési) and intrastrain variability was considered by using 20 homokaryotic and 50 controlled dikaryotic mycelia belonging to the progeny of one laboratory fruiting strain of this species.The range of variation of IAA-synthesizing activity was of the same order of magnitude within the four groups considered. No correlation was detected between, on one hand, the IAA-synthesizing activity of the mycelia and, on the other hand, their taxonomic position, their geographic origin, or their host plant.Within the progeny of one H. cylindrosporum fruiting strain, 15 of the 50 controlled dikaryons presented an activity higher than that of the original dikaryon. The variation among dikaryons could not be strictly related to the variation in parental homokaryons, indicating that genetic control of this activity probably involves a nonadditive component. Significant additive and nonadditive components of the genetic variation were detected, each of them representing about 50% of the total variation. The nonadditive heritable component could not be explained by a model involving only dominance.     

ARAGONITE CRYSTALS IN SPIROGYRA SP. (CHLOROPHYTA)

Intracellular crystals of aragonite have been identified by selected area electron diffraction (SAED) in a species of the freshwater filamentous alga Spirogyra from the Thames River, Ontario, Canada. The crystals are 2 to 24 μm in diameter, and characterized by a unique cross-shaped morphology, in which needle-like, or prismatic outgrowths develop from a common axis. Crystals may be dispersed throughout filaments, but tend to cluster as aggregates towards the centre .     

Influence of adrenergic receptors on ovarian progesterone secretion in the pseudopregnant cat and oestradiol secretion in the oestrous cat

The infusion of isoprenaline or propranolol into the abdominal aorta of the pseudopregnant cat caused an increase or decrease respectively in the ovarian progesterone secretion rate. These observations suggest that the sympathetic innervation of the ovary has a physiological influence on normal progesterone secretion, and this mechanism may explain stress-related increases in progesterone concentrations. The infusion of isoprenaline or propranolol after the stimulation of follicular growth had no consistent or convincing effect on oestradiol secretion.     

Regulation of the length of the fertile period in the domestic fowl by numbers of oviducal spermatozoa, as reflected by those trapped in laid eggs

The numbers of spermatozoa trapped in the vitelline membrane of laid eggs were counted after staining with the fluorochrome 2,4-diamidino-2-phenylindole. In a group of 24 hens inseminated with different numbers of spermatozoa to produce different lengths of fertile periods, the numbers of spermatozoa in successive eggs from each hen decreased logarithmically with respect to days following insemination. A relationship could be described between the numbers of spermatozoa per unit area of membrane of an egg and the probability of that egg being fertile. After insemination the number of spermatozoa on successively-laid eggs appears to become reduced until a critical value is reached, after which the hen will lay infertile eggs. By estimating the day on which the critical value was achieved, the actual length of the fertile period could be predicted. It is suggested that the numbers of spermatozoa trapped in the vitelline membrane of laid eggs represent those which surround the ovum at the time of fertilization.     

Oral ontogeny of the Ayu, Plecoglossus altivelis and comparisons with the jaws of other salmoniform fishes

The Japanese Ayu, Plecoglossus altivelis Temminck & Schlegel is the sole representative of the salmoniform family Plecoglossidae. The Ayu is remarkable for its dentition which in adults comprises groups of diagonally arranged comb-like teeth in the outer tissue of the jaws. In juveniles (below 63 mm SL) the teeth are attached normally to the jaws. The transition of tooth form is correlated with a switch from zooplanktivory to algal or aufwuchs grazing. The present study follows the development of the teeth, jaws, oral cavity ethmoid and suspensorial elements in specimens ranging in size from 41–70 mm SL. The possible mode of function of the adult dentition is discussed. Comparisons are made with the jaws of other salmoniform fishes and a suite of supposed apomorphic characters are identified which are also shared with certain genera of the family Osmeridae, thus supporting the ideas of others that the Osmeridae is a paraphyletic assemblage.     

The probability with which EMS-initiated mutagenic lesions generate mutations in CHO cells

In this note we distinguish between multiple mutations affecting a given locus which are generated at separate error-prone lesions and multiple independent mutations generated at a single error-prone lesion. We describe a basis for determining the probability with which the latter class of mutations occurs based on the mutant fraction in the progeny and determine an average probability of 0.6 mutations/replication/mutagenic site for those EMS-modified sites which are mutagenic for G6PDH activity in CHO cells.