Hydrogen Cyanide Production due to Mid-Size Impacts in a Redox-Neutral N2-Rich Atmosphere

Cyanide compounds are amongst the most important molecules of the origin of life. Here, we demonstrate the importance of mid-size (0.1–1 km in diameter) hence frequent meteoritic impacts to the cyanide inventory on the early Earth. Subsequent aerodynamic ablation and chemical reactions with the ambient atmosphere after oblique impacts were investigated by both impact and laser experiments. A polycarbonate projectile and graphite were used as laboratory analogs of meteoritic organic matter. Spectroscopic observations of impact-generated ablation vapors show that laser irradiation to graphite within an N₂-rich gas can produce a thermodynamic environment similar to that produced by oblique impacts. Thus, laser ablation was used to investigate the final chemical products after this aerodynamic process. We found that a significant fraction (>0.1 mol%) of the vaporized carbon is converted to HCN and cyanide condensates, even when the ambient gas contains as much as a few hundred mbar of CO₂. As such, the column density of cyanides after carbon-rich meteoritic impacts with diameters of 600 m would reach ~10 mol/m² over ~10² km² under early Earth conditions. Such a temporally and spatially concentrated supply of cyanides may have played an important role in the origin of life.     

Endogenous abscisic acid is involved in methyl jasmonate-induced reactive oxygen species and nitric oxide production but not in cytosolic alkalization in Arabidopsis guard cells

We recently demonstrated that endogenous abscisic acid (ABA) is involved in methyl jasmonate (MeJA)-induced stomatal closure in Arabidopsis thaliana. In this study, we investigated whether endogenous ABA is involved in MeJA-induced reactive oxygen species (ROS) and nitric oxide (NO) production and cytosolic alkalization in guard cells using an ABA-deficient Arabidopsis mutant, aba2-2, and an inhibitor of ABA biosynthesis, fluridon (FLU). The aba2-2 mutation impaired MeJA-induced ROS and NO production. FLU inhibited MeJA-induced ROS production in wild-type guard cells. Pretreatment with 0.1 μM ABA, which does not induce stomatal closure in the wild type, complemented the insensitivity to MeJA of the aba2-2 mutant. However, MeJA induced cytosolic alkalization in both wild-type and aba2-2 guard cells. These results suggest that endogenous ABA is involved in MeJA-induced ROS and NO production but not in MeJA-induced cytosolic alkalization in Arabidopsis guard cells.     

Isolation and Chemical Characterization of a Mating Pheromone Produced by Saccharomyces kluyveri

The pullulanase gene (pul) of Klebsiella aerogenes was transferred in vivo to Escherichia coli by using RP4:: Mu cts. The pul gene was expressed in E. coli, although the level of pullulanase activity in E. coli was lower than that in K. aerogenes, and the Pul⁺ transconjugants were relatively unstable in an unselective medium. Production of pullulanase, which is used to make maltose from starch, was induced in E. coli by pullulan, waxy maize amylopectin, soluble starch and maltose. When the transconjugant cells of E. coli were grown with pullulan or maltose, most pullulanase was produced intracellularly, whereas K. aerogenes produced pullulanase extracellularly. Retransfer of the pul_k gene from E. coli to K. aerogenes by conjugation resulted in an increase of the production of extracellular pullulanase.     

Isolation and Identification of a Sexual Hormone in Yeast

5-Fluorotryptophan (5FT), indolmycin (IM), 4-fluorotryptophan and 7-azatryptophan were found on screening to be tryptophan antagonists among various chemically synthesized and naturally occurring tryptophan analogues for the isolation of l-tryptophan (l-Trp) producing mutants of Bacillus subtilis K.

From among 5FT resistant mutants, potent l-Trp producers were obtained using an improved isolation medium. Growth of the isolated 5FT-resistant l-Trp producer, AJ 11709, was inhibited by IM. From among 5FT and IM resistant mutants, the best strain, AJ 11979, which produced 9.0 g/liter of l-Trp from 13% glucose on 120hr cultivation, was selected.     

Substrate Specificity of α-Glucosidase II in Rice Seed

The substrate specificity of rice α-glucosidase II was studied. The enzyme was active especially on nigerose, phenyl-α-maltoside and maltooligosaccharides. The actions on isomaltose and phenyl-α-glucoside were weak, and on sucrose and methyl-α-glucoside, negligible. The α-glucans, such as soluble starch, amylopectin, β-limit dextrin, glycogen and amylose, were also hydrolyzed.

The ratio of the maximum velocities for hydrolyses of maltose (G₂), nigerose (N), kojibiose (K), isomaltose (I), phenyl-α-maltoside (?M) and soluble starch (SS) was estimated to be 100: 94.4: 14.2: 7.1: 89.5: 103.1 in this order, and that for hydrolyses of malto-triose (G₃), -tetraose (G₄), -pentaose (G₅), -hexaose (G₆), -heptaose (G₇), -octaose (G₈), and amyloses ( and ), 113: 113: 113: 106: 113: 100: 106: 106. The Km values for N, K, I, ?M and SS were 2.4 mm, 0.58 mm, 20 mm, 1.6 mm and 5.0 mg/ml, respectively; those for G₂, G₃, G₄, G₅, G₆, G₇, G₈, and , 2.4 mm, 2.2 mm, 2.1 mm, 1.5 mm, 1.0 mm, 1.1 mm, 0.95 mm, 1.5 mm and 1.1 mm.

Rice α-glucosidase II is considered an enzyme with a preferential activity on maltooligosaccharides.     

Partial Purification and Some Properties of ADP-glucose Phosphorylase from Potato Tubers

ADP-glucose phosphorylase [adenosine diphosphate glucose: orthophosphate adenyl- yltransferase; Dankert et ah, Biochim. Biophys. Acta, 81, 78 (1964)] was found to be widely distributed in plant tissues. The enzyme was purified 570-fold in a 24% yield from cell- free extract of growing tubers of potato (Solanum tuberosum L.). The following reaction catalyzed by the purified enzyme was found to proceed stoichiometrically. ADP-glucose +P₁→ADP+glucose-1-P

Maximal activity was observed at pH 8. The enzyme was the most stable at pH 7, showing 50% loss of its original activity after 50 min heating at 57°C. The following kinetic parameters were obtained: activation energy, 11.1 kcal/mole; Km (P₁), 2.5 mm; Km (ADP-glucose), 0.05 mm. The enzyme did not act on GDP-mannose, GDP-glucose and UDP-glucose. Neither activator nor inhibitor was found among various phosphorylated metabolites tested. The enzyme was inhibited by metal-binding reagents, EDTA and o-phenanthroline. None of the metal ions tested was found to recover the activity of chelator-treated enzyme.