Purification and properties of acetyl-CoA:L-glutamate N-acetyltransferase from human liver.

Acetyl-CoA:L-glutamate N-acetyltransferase (amino acid acetyltransferase, EC 2.3.1.1) was isolated from human liver mitochondria by precipitation with (NH4)2SO4 and chromatography on hydroxyapatite, DEAE-cellulose and Sephacryl 300. This gave a 360-fold purification. The molecular weight was estimated to be approx. 190 000. The kinetic properties in the absence of arginine are compatible with a rapid-equilibrium random Bi Bi mechanism. The estimated constants are: for the substrates Km,acetyl-CoA 4.4 mM, Ki,acetyl-CoA 4.7 mM, Km,glutamate 8.1 mM, Ki,glutamate 8.8 mM; for the products, Ki,acetylglutamate 0.28 mM, Ki,CoA 5.6 mM. The rate constant for the forward direction is 1.24s-1. If in vivo the constants are of the same order of magnitude as in vitro, the synthesis of N-acetylglutamate, an obligate activator of the first step of urea synthesis, can be expected to occur in the mitochondrion under conditions where the amino acid acetyltransferase is not saturated by its substrates. The regulation of the first step of urea synthesis could thus depend mainly on the intramitochondrial substrate and perhaps product concentrations of amino acid acetyltransferase.     

Serotonin and γ-Aminobutyric Acid Turnover After Injection into the Median Raphe of Substance P and D-Ala-Met-Enkephalin Amide

The raphe nuclei [which contain serotonin (5-HT) cell bodies] are also known to contain axons that store substance P, met-enkephalin, and gamma-aminobutyric acid (GABA). We have previously shown that GABA has a tonic inhibitory action on 5-HT turnover. To examine other possible interactions of these neuronal systems, we assessed the effect on 5-HT turnover of injecting substance P and 2-D-ala-met-enkephalin into the median raphe nucleus, and the effects of substance P on GABA turnover. Serotonin turnover was increased by 30% in the hippocampus after the injection of substance P (4 micrograms) into the median raphe, indicating an excitatory effect of substance P on the raphe-hippocampal system. Local injection of the metabolically stable metenkephalin analog 2-D-ala-met-enkephalin amide (10 micrograms) increased the hippocampal steady state content of 5-hydroxyindoleacetic acid (5-HIAA) by 60%. The data suggest an excitatory effect of met-enkephalin within the raphe nucleus. We attempted to estimate GABA turnover from the rate of disappearance of GABA after inhibition of glutamic acid decarboxylase by isoniazid and by the rate of accumulation of GABA after inhibition of GABA transaminase by gabaculine. Isoniazid, which is a competitive inhibitor, had too short and incomplete an action to be of use when injected intranuclearly. Gabaculine, which is an irreversible inhibitor, induced a rapid-onset increase in GABA content. This accumulation was linear up to 90 min. The injection fo gabaculine (80 ng) into the raphe increased GABA content by five times the control values, but hippocampal 5-HT and 5-HIAA contents were not significantly changed. Substance P injection increased the GABA turnover by 30%. Gabaculine seems a promising tool for detecting changes in GABA turnover.     

Relationships between growth,cyclic amp and tylosin production in two mutants of Streptomyces fradiae

Summary A mutant of S. fradiae producing higher amounts of tylosin than its parent also showed higher intracellular cAMP and DNA. Similarly the addition of chloroquine to producing cultures of the parent strain significantly increased the production of tylosin, cAMP, and DNA. The most likely hypothesis is that cAMP acts on tylosin production through a stimulation of the synthesis of DNA, which may prevent aging of the producing cells and lead to higher overvall antibiotic production.     

Thiaisoleucine and protein synthesis.

Thiaisoleucine is an isoleucine analogue having the gamma-methylene group of the valerianic carbon chain substituted by a sulphur atom. It has been demonstrated that thiaisoleucine is activated and transferred to tRNAIle by rat liver aminoacyl-tRNA synthetase and inhibits isoleucine incorporation into polypeptides in protein synthesizing systems from rat liver or rabbit reticulocytes, whereas it does not affect either leucine incorporation or ribosome run-off or polypeptide chain elongation rate. All tests were performed in comparison with O-methyl-threonine, an isoleucine analogue with the gamma-methylene group substituted by an oxygen atom. In all the reactions studied, both thiaisoleucine and O-methyl-threonine act as competitive inhibitors of isoleucine. With respect to O-methyl-threonine, thiaisoleucine shows higher activity as an isoleucine inhibitor.     

Molecular structural effects involved in the interaction of anthracyclines with DNA.

Changes in DNA binding ability of daunomycin following structural modifications in the aglycone moiety have been studied by the fluorescence quenching method and by thermal denaturation of the complex. Removal of the methoxyl group at position 4 leads to a slightly stronger binding. Changes in the position of the glycosidic linkage result in a markedly weaker binding. Removal of the hydroxyl group at position 9, with the concomitant formation of a 9,10-anhydro derivative, decreases the binding ability. Methylation of hydroxyl groups at C-6 and C-11 leads to an inactive derivative and makes the binding affinity disappear almost completely. Structure-activity correlations for the DNA binding reaction deduced from these studies are in agreement with earlier findings that relate to the biological activity and confirm the general picture of the binding mechanism.     

Synthesis and chromatographic properties of Se-carboxymethyl-selenohomocysteamine (2-carboxymethyl, 3-aminopropyl selenide)

Details are reported for the synthesis of Se-carboxymethylselenohomocysteamine from selenohomocysteamine and monochloroacetic acid. Data on its behaviour on paper and ion-exchange chromatography are also reported, which allow its identification.     

Effects of diffusible products of peroxidation of rat liver microsomal lipids

The effects on cellular structures of products of peroxidation of rat liver microsomal lipids were investigated. A system containing actively peroxidizing liver microsomal fraction was separated from a revealing or target system by a dialysis membrane. The target system, contained in the dialysis tube, consisted of either intact cells (erythrocytes) or subcellular fractions (liver microsomal fraction). When liver microsomal fractions were incubated with NADPH (or an NADPH-generating system), lipid peroxidation, as measured by the amount of malonaldehyde formed, occurred very rapidly. The malon-aldehyde concentration tended to equilibrate across the dialysis membrane. When the target system consisted of erythrocytes, haemolysis occurred abruptly after a lag phase. The lysis was greatly accelerated when erythrocytes from vitamin E-deficient rats were used, but no haemolysis was observed when erythrocytes from vitamin E-treated rats were used. When, in the same system, freshly prepared liver microsomal fractions were exposed to diffusible factors produced by lipid peroxidation, the glucose 6-phosphatase activity markedly decreased. A similar decrease in glucose 6-phosphatase activity, as well as a smaller but significant decrease in cytochrome P-450, was observed when the target microsomal fractions were exposed to diffusible factors derived from the peroxidation of liver microsomal lipids in a separate preincubation step. These and additional experiments indicated that the toxicological activity is relatively stable. Experiments in which the hepatic microsomal fractions destined for lipid peroxidation contained radioactively labelled arachidonic acid, previously incorporated into the membranes, showed that part of the radioactivity released from the microsomal fraction into the incubation medium entered the dialysis tube and was recovered bound to the constituents of the microsomal fractions of the target system. These results indicate that during the course of the peroxidation of liver microsomal lipids toxic products are formed that are able to induce pathological effects at distant loci.     

Delayed hypersensitivity and Ig level in 210 patients with chronic myeloid leukemia

Summary Serum immunoglobulin concentration and skin reactivity to at least three recall antigens were determined in 210 patients with chronic myeloid leukemia (CML). Immunoglobulin concentration was normal in the great majority of the patients. Skin tests were negative in 50 of 210 cases (24%). No relationship could be demonstrated between skin reactivity, age, time since diagnosis, WBC, lymphocyte count, and splenectomy. Prior antileukemic therapy was a major factor in determining the response to skin tests.S. Tura (Chairman) and M. Baccarani (Secretary), Cattedra di Ematologia dell'Università e Servizio di Ematologia dell'Ospedale S. Orsola, Bologna; G. de Sandre, G. Perona, G. Cetto, G. Pizzolo, Istituto di Patologia Medica e Cattedra di Ematologia dell'Università, Verona; P. Rambotti, B. Falini, Clinica Medica dell'Università, Perugia; T. Chisesi, G. Capnist, Divisione di Ematologia, Ospedale Civile, Vicenza; A. Cajozzo, P. Citarella, Cattedra di Ematologia dell'Università, Palermo; G. Broccia, Sezione di Ematologia, Ospedale Armando Businco, Cagliari; V. Liso, G. Troccoli, Clinica Medica II dell'Università, Bari; L. Bruzzese, G. Nappi, A. Abbadessa, Clinica Medica (I Facoltà) dell'Università, Napoli; A. Porcellini, C. Delfini, Divisione di Ematologia, Ospedali Riuniti, Pesaro; E. Cacciola, R. Giustolisi, R. Musso, V. Raimondi, Cattedra di Ematologia dell'Università, Catania; G. Torlontano, L. Geraci, Cattedra di Ematologia dell'Università, Chieti, e Divisione di Ematologia, Ospedale Civile, Pescara; F. Mandelli, G. Mariani, B. Monarca, N. Petti, Cattedra di Ematologia dell'Università, Roma; R. di Guglielmo, A. Miliani, Clinica Medica dell'Università, Firenze; C. Bernasconi, M. Lazzarino, G. Castelli, Divisione di Ematologia, Ospedale S. Matteo, Pavia; A. Alberti, S. Magro, Servizio di Ematologia, Ospedale Generale Regionale, Catanzaro; A. Neri, P. Iacopino, Divisione di Ematologia, Ospedali Riuniti, Reggio Calabria; R. Delsignore, M. C. Baroni, Istituto di Patologia Medica dell'Universita, Parma; E. Bajetta, S. Monfardini, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milano; S. Tognella, Istituto Scientifico di Medicina Interna, Cattedra di Clinica Medica 2R, Università, Genova.