Re-evaluation of the hypoxia theory as the mechanism of hyperventilation-induced EEG slowing.

To determine whether the well-accepted hypoxia theory accounts for hyperventilation-induced electroencephalogram (EEG) slowing, the authors monitored changes in cerebral oxygenation and end-tidal concentrations of carbon dioxide in 67 patients with epilepsy (age range = 5-12 years) during the hyperventilation activation test in a routine EEG examination. Relative concentration changes in cerebral oxygenated, deoxygenated, total hemoglobin, and oxidized cytochrome oxidase were measured by near-infrared spectroscopy in the frontal region. In all patients, except one who demonstrated EEG slowing, total and oxygenated hemoglobin decreased, and cytochrome oxidase was not reduced. EEG slowing occurred intermittently in 22 patients and was not synchronous with changes in either the cerebral oxygenation or end-tidal concentration of carbon dioxide. The degree of EEG slowing was diminished or the slow waves disappeared abruptly within 1 second after the cessation of hyperventilation in 22 patients when both the cerebral oxygenation and end-tidal concentration of carbon dioxide were still at low levels. The findings during the recovery periods do not confirm the hypoxia theory. It is thus supposed that more subtle mechanisms are the cause of EEG slowing.

Cloning and inactivation of genes encoding ferredoxin- and NADH-dependent glutamate synthases in the cyanobacterium plectonema boryanum. Imbalances In nitrogen and carbon assimilations caused by deficiency of the ferredoxin-dependent enzyme

Glutamate synthase (GOGAT) is a key enzyme in the assimilation of inorganic nitrogen in photosynthetic organisms. We found that, like higher plants, the facultative heterotrophic cyanobacterium Plectonema boryanum had ferredoxin (Fd)- and NADH-dependent GOGATs. The genes glsF, gltB, and gltD were cloned, and structural analyses and target mutageneses demonstrated that glsF encoded Fd-GOGAT and that gltB and gltD encoded the two subunits of NADH-GOGAT. All three mutants lacking one of the GOGAT genes were able to grow photosynthetically and heterotrophically. However, the Fd-GOGAT mutant exhibited a phenotype of marked nitrogen deficiency when grown under conditions of saturating illumination and CO2 supply. In these conditions the rate of the ammonia uptake from the culture medium was slower in the Fd-GOGAT mutant than in the wild type or in the NADH-GOGAT mutant, but no significant differences were found in the rate of the CO2 fixation-dependent O2 evolution among these strains. Our results suggest that, although both Fd- and NADH-GOGATs were operative in the cells growing in light, the contribution of Fd-GOGAT, which directly utilizes photoreducing power for the catalytic reaction, is essential for balancing photosynthetic nitrogen and carbon assimilation.

Purification and characterization of three distinct types of phospholipase A2 inhibitors from the blood plasma of the Chinese mamushi, Agkistrodon blomhoffii siniticus.

Three distinct types of phospholipase A2 (PLA2) inhibitory proteins (PLIalpha, PLIbeta, and PLIgamma) were isolated from the blood plasma of the Chinese mamushi, Agkistrodon blomhoffii siniticus. PLIalpha is an inhibitor that we have already purified and whose amino acid sequence we have already determined [Ohkura, Inoue, Ikeda and Hayashi (1993) J. Biochem. (Tokyo) 113, 413-419]. It inhibited selectively the group-II acidic PLA2s from Crotalidae venom. PLIbeta was a 160-kDa glycoprotein having a trimeric structure composed of 50-kDa subunits. The amino acid sequence of the first 30 amino acids of the N-terminal part of the 50-kDa subunit was determined and found to have no significant homology to that of known proteins. PLIbeta was a selective inhibitor against the group-II basic PLA2s from Crotalidae venom. Some amino acid residues located in or close to the interfacial binding surface of the group-II basic PLA2s were suggested to be involved in selective binding to PLIbeta. PLIgamma was a 100-kDa glycoprotein containing 25-kDa and 20-kDa subunits and inhibited all of the PLA2s investigated equally, including Elapidae venom PLA2s (group I), Crotalidae and Viperidae venom PLA2s (group II) and honey-bee PLA2 (group III). From the N-terminal sequences of the two subunits, PLIgamma was found to be the same type of PLI that had been purified from Thailand cobra plasma.