Glutamate Oxidation by Soybean Cotyledon and Leaf Mitochondria

Mitochondria purified from cotyledons of soybean seedlings fiveto ten days old have the capacity to rapidly oxidize glutamate(measured as glutamate dependent oxygen consumption). This capacitywas greatest at ten days after planting but was very low priorto emergence of cotyledons from the vermiculite and during senescence.Solubilized glutamate dehydrogenase activity, on the other hand,was substantial at two days after planting, peaked at sevendays, then declined and rose again during senescence. It issuggested that mitochondrial glutamate oxidation plays a rolein reserve mobilization and amino acid metabolism during seedlinggrowth. Leaf mitochondria and those from senescing cotyledonscould not sustain rapid rates of glutamate oxidation despiteready oxidation of other substrates and high solubilized glutamatedehydrogenase activity, suggesting an alternative role for theenzyme in these tissues. Possible controlling factors are discussed. ² Present address, Garvan Institute, Darlinghurst, N. S. W.,Australia. ³ Permanent address, Department de Biologia Vegetal, Facultatde Biologia, Universitat de Barcelona, Barcelona, Spain. (Received May 6, 1988; Accepted August 3, 1988)     

Inverted neurons in agyria

Summary An anatomoclinical observation of agyria is reported. The karyotype revealed a partial deletion of the short arm of chromosome 17. The etiology of agyria is reviewed in the light of this chromosomal abnormality. In addition we describe the peculiar pattern of neurons in the cortex: Golgi stain demonstrated many inverted pyramidal cells in the superficial part of the cortical layer. The mechanism of this abnormality is discussed.     

Polyamine Limitation of Growth Slows the Rate of Polypeptide Chain Elongation in Escherichia coli

The rate of polypeptide chain elongation during steady-state, polyamine-limited growth of a mutant of Escherichia coli was measured by two independent techniques. Analysis of polysome patterns gave values of 17.5 and 9.5 amino acids per s at 37 C in unstarved and polyamine-limited cells, respectively. From the kinetics of entry of labeled amino acids into polypeptides of defined molecular weights, values at 30 C of 10.1 and 5.8 amino acids per s were obtained for unstarved and polyamine-limited cultures, respectively. Correction of these values to 37 C resulted in rates of 15.0 and 8.7 amino acids per s. These results support the previous conclusion, based on the kinetics of beta-galactosidase induction, that polyamine starvation decreases the rate of protein synthesis by limiting the velocity of polypeptide chain elongation.     

A comparison of the effects of NN′-dicyclohexylcarbodi-imide, oligomycin A and aurovertin on energy-linked reactions in mitochondria and submitochondrial particles

1. The effects of dicyclohexylcarbodi-imide, oligomycin A and aurovertin on enzyme systems related to respiratory-chain phosphorylation were compared. Dicyclohexylcarbodi-imide and oligomycin A have very similar functional effects, giving 50% inhibition of ATP-utilizing and ATP-generating systems at concentrations below 0.8nmole/mg. of submitochondrial-particle protein. Aurovertin is a more potent inhibitor of ATP synthesis, giving 50% inhibition at 0.2nmole/mg. of protein. However, aurovertin is a less potent inhibitor of ATP-utilizing systems: the ATP-driven energy-linked nicotinamide nucleotide transhydrogenase is 50% inhibited at 3.0nmoles/mg. of protein and the ATP-driven reduction of NAD(+) by succinate is 50% inhibited at 0.95nmole/mg. of protein. 2. With EDTA-particles (prepared by subjecting mitochondria to ultrasonic radiation at pH9 in the presence of 2mm-EDTA) the maximum stimulation of the ATP-driven partial reactions is effected by similar concentrations of oligomycin A and dicylcohexylcarbodi-imide, but the latter is less effective. The stimulatory effects of suboptimum concentrations of dicyclohexylcarbodi-imide and oligomycin A are additive. Aurovertin does not stimulate these reactions or interfere with the stimulation by the other inhibitors. 3. Dicyclohexylcarbodi-imide and oligomycin A stimulate the aerobic energy-linked nicotinamide nucleotide transhydrogenase of EDTA-particles, but the optimum concentration is higher than that required for the ATP-driven partial reactions. Aurovertin has no effect on this reaction. 4. The site of action of dicyclohexylcarbodi-imide is in CF(0), the mitochondrial fraction that confers oligomycin sensitivity on F(1) mitochondrial adenosine triphosphatase.     

Genetic Basis of Colicin E Susceptibility in Escherichia coli I. Isolation and Properties of Refractory Mutants and the Preliminary Mapping of Their Mutations

Colicin E-resistant mutants were isolated in Escherichia coli K-12 which, although still apparently possessing the E receptor and adsorbing colicin, were nevertheless insensitive (refractory) to its effect. Eight phenotypic groups were obtained, but some mutants from three of these groups were all shown to map at gal, whereas a second refractory locus, giving resistance to E1 alone, mapped close to thy. It is suggested that the successful fixation of any of the three distinct colicins of group E may involve a dual role for the cell surface "receptor," the first for the binding of the protein and the second for the correct orientation of the bound molecule relative to the cytoplasmic membrane. The majority of the refractory mutants isolated may derive from changes in components concerned with the second of these receptor functions. Two groups of mutants, however, refractory to only E1 or E2, probably reflect changes in the intracellular transmission systems which specifically mediate the effects of these two colicins, the changes not allowing transmission through the cytoplasmic membrane to the respective targets of the colicins. The E1 adsorption site was shown to be distinct from that for E2 and E3, indicating an early separation of the colicin E transmission systems.     

Effect of ethylenediaminetetraacetic acid-Tris(hydroxymethyl)aminomethane on release of the acid-soluble nucleotide pool and on breakdown of ribosomal ribonucleic acid in Escherichia coli

Brief treatment of Escherichia coli with 2 x 10(-4)m ethylenediaminetetraacetic acid (EDTA)-0.12 m tris(hydroxymethyl)aminomethane (Tris), pH 8.0, or 0.12 m Tris alone resulted in the release of the acid-soluble nucleotide pool at 3 or 23 C. Exposure to EDTA-Tris for up to 90 min at 3 C did not result in the release of increasing amounts of 260-mmu-absorbing material. At 23 and 37 C, EDTA-Tris resulted in a steady increase in acid-soluble 260-mmu-absorbing material. Previous growth environment did not alter the release. There appeared to be degradation of 23S ribonucleic acid (RNA) after 10 min of exposure at 23 C. In addition, there was degradation of nucleotides to nucleosides and bases. This occured either within the cells with altered permeability or in the periplasmic space. This occurred in the presence of EDTA and Tris but was not seen with EDTA-phosphate. The mechanism of this degradation is unclear, since it occurs in ribonuclease I-deficient strains. Exposure to Tris buffer for long periods of time at 23 C resulted in release of the nucleotide pool and in degradation of RNA and nucleotides. These studies point out that the EDTA-Tris effect on E. coli must be divided into two parts, an early (4 to 5 min) change in permeability and a later phase of actual RNA breakdown and nucleotide degradation. Studies utilizing EDTA and Tris as agents altering permeability must thus be viewed with caution. Although the cells are viable, they have lost their acid-soluble nucleotide pool and have undergone degradation of some ribosomal RNA.     

Release of surface enzymes in Enterobacteriaceae by osmotic shock

The process of osmotic shock, which has been used to release degradative enzymes from Escherichia coli, can be applied successfully to other members of the Enterobacteriaceae. Cyclic phosphodiesterase (3'-nucleotidase), 5'-nucleotidase (diphosphate sugar hydrolase), acid hexose phosphatase, and acid phenyl phosphatase are released from Shigella, Enterobacter, Citrobacter, and Serratia strains. Some strains of Salmonella also release these enzymes. Members of Proteus and Providencia groups fail to release enzymes when subjected to osmotic shock and do not show a lag in regrowth, although they do release their acid-soluble nucleotide pools. In contrast to E. coli, release of enzymes from other members of the Enterobacteriaceae studied is affected by growth conditions and strain of organism. None of the organisms was as stable to osmotic shock in exponential phase of growth as was E. coli. Exponential-phase cells of Shigella, Enterobacter, and Citrobacter could be shocked only with 0.5 mm MgCl(2) to prevent irreparable damage to the cells. These observations suggest that this group of degradative enzymes is probably loosely bound to the cytoplasmic membrane through the mediation of divalent cations.