The mouse Gm853 gene encodes a novel enzyme: Leucine decarboxylase

Ornithine decarboxylase (ODC) is a key enzyme in the biosynthesis of polyamines. ODC-antizyme inhibitors (AZINs) are homologous proteins of ODC, devoid of enzymatic activity but acting as regulators of polyamine levels. The last paralogue gene recently incorporated into the ODC/AZINs family is the murine Gm853, which is located in the same chromosome as AZIN2, and whose biochemical function is still unknown. By means of transfection assays of HEK293T cells with a plasmid containing the coding region of Gm853, we show here that unlike ODC, GM853 was a stable protein that was not able to decarboxylate l-ornithine or l-lysine and that did not act as an antizyme inhibitor. However, GM853 showed leucine decarboxylase activity, an enzymatic activity never described in animal cells, and by acting on l-leucine (Km = 7.03 × 10^? 3 M) it produced isopentylamine, an aliphatic monoamine with unknown function. The other physiological branched-chain amino acids, l-valine and l-isoleucine were poor substrates of the enzyme. Gm853 expression was mainly detected in the kidney, and as Odc, it was stimulated by testosterone. The conservation of Gm853 orthologues in different mammalian species, including primates, underlines the possible biological significance of this new enzyme. In this study, we describe for the first time a mammalian enzyme with leucine decarboxylase activity, therefore proposing that the gene Gm853 and its protein product should be named as leucine decarboxylase (Ldc, LDC).     

The enzymes of biotin dependent CO2 metabolism: What structures reveal about their reaction mechanisms

Biotin is the major cofactor involved in carbon dioxide metabolism. Indeed, biotin‐dependent enzymes are ubiquitous in nature and are involved in a myriad of metabolic processes including fatty acid synthesis and gluconeogenesis. The cofactor, itself, is composed of a ureido ring, a tetrahydrothiophene ring, and a valeric acid side chain. It is the ureido ring that functions as the CO₂ carrier. A complete understanding of biotin‐dependent enzymes is critically important for translational research in light of the fact that some of these enzymes serve as targets for anti‐obesity agents, antibiotics, and herbicides. Prior to 1990, however, there was a dearth of information regarding the molecular architectures of biotin‐dependent enzymes. In recent years there has been an explosion in the number of three‐dimensional structures reported for these proteins. Here we review our current understanding of the structures and functions of biotin‐dependent enzymes. In addition, we provide a critical analysis of what these structures have and have not revealed about biotin‐dependent catalysis.     

Conjugated polyamines and reproductive development: Biochemical, molecular and physiological approaches

Whole tobacco plants containing the root-inducing, left-hand transferred DNA (Ri TL-DNA) display a transformed phenotype, that includes alterations in a number of developmental processes, such as floral induction, flowering and reproduction. We show that the entire Ri TL-DNA is responsible for repression of ornithine and tyrosine decarboxylases while it exerts no effect on transferase and the methyl transferase activities. Evidence is provided that two genes from the Ri TL-DNA, rolA and rolC, alter polyamine metabolism as well as floral induction and flowering. Thus, plants transformed by the rolC gene (under the control of the 35S promoter from cauliflower mosaic virus) were male-sterile (non-viable pollen) and female fertility was reduced by approximatively 80%. A constitutive overexpression of the rolC gene may directly or indirectly cause inhibition of the accumulation of water-insoluble amine conjugates located in the anthers and all the methyl transferases, leading to increases of ornithine decarboxylase, phenylalanine ammonia lyase and putrescine caffeoyl-CoA transferase. The results suggest that male sterility is associated with catabolic processes exerted at the level of water-insoluble amine conjugates and support the view that diamine oxidase may be involved in the regulation of the amine concentration during sexual differentiation, a factor that should be considered when attempting to decipher the mechanisms of control of sexual differentiation. The rolC gene could be useful in determining the role of diamine oxidase in the physiology of flowering. These results suggest that elevated free polyamine and water-soluble polyamine levels (located in the ovaries) contribute to abnormal floral development. The transformed phenotype due to P_35S-rolA(the rolA gene fused to the 35S promoter) consisted of inhibited or delaved flowering, and altered floral morphology in the form of flower abortion. The effects of P_35S-rolA on flowering and fertility are closely correlated with limitations in the accumulation of the water-soluble and -insoluble amine conjugates and increase in accumulation of free amines, indicating that amine conjugates (via transferases) have important functions in floral induction, floral evocation and reproduction. Spermidine availability as well as tyramine availability (in conjugated forms) could be limiting factor(s) in sexual development in tobacco.     

Changes in amino acid decarboxylation in maize (Zea mays; Poaceae) tissues in response to bird cherry-oat aphid (Rhopalosiphum padi; Aphididae) infestation

The study was focused on changes in the activities of ornithine decarboxylase (ODC), lysine decarboxylase (LDC) and tyrosine decarboxylase (TyDC) in maize seedlings infested by bird cherry-oat aphid (Rhopalosiphum padi L.).Obtained results showed that the aphid infestation induced LDC activity strongly within tissues of less aphid-settled maize (Waza cv.) during the first week of the infestation in comparison to the control plants and the activity was suppressed after two weeks. However, TyDC activity fluctuated under the aphid infestation. In relation to the control, the enzyme activity was inhibited on the first day, activated after the first week and reduced again two weeks into the experiment. A significant reduction in ODC activity was also observed in seedlings of aphid-infested maize Waza cv. during the first week. In a more susceptible maize cv. (Złota Karłowa), an increase in LDC and TyDC activities in relation to the control and a simultaneous decrease in ODC activity were noted after the first day of the infestation. After one week of aphid attack, TyDC activity was induced and ODC was inhibited, whereas after two weeks ODC activity was decreased with a simultaneous increase in LDC activity in the Złota Karłowa seedlings.