Dihydroquercetin accumulation in the medium of some wild carrot culture subclones

Approximately half of the subclones examined from one clone of the wild carrot cell culture WC63-1-9-1 accumulated dihydroquercetin in the culture medium. The amount of dihydroquercetin accumulated in the medium varied with the subclone used, the size of the inoculum, the medium used and the time of sampling.Dedicated to Dr. Friedrich Constabel on the occasion of his 60th birthday     

Distribution of δ-aminolevulinic acid biosynthetic pathways among phototrophic bacterial groups

Two biosynthetic pathways are known for the universal tetrapyrrole precursor, -aminolevulinic acid (ALA). In the ALA synthase pathway which was first described in animal and some bacterial cells, the pyridoxal phosphate-dependent enzyme ALA synthase catalyzes condensation of glycine and succinyl-CoA to form ALA with the loss of C-1 of glycine as CO₂. In the five-carbon pathway which was first described in plant and algal cells, the carbon skeleton of glutamate is converted intact to ALA in a proposed reaction sequence that requires three enzymes, tRNA^Glu, ATP, Mg²⁺, NADPH, and pyridoxal phosphate. We have examined the distribution of the two ALA biosynthetic pathways among various genera, using cell-free extracts obtained from representative organisms. Evidence for the operation of the five-carbon pathway was obtained by the measurement of RNase-sensitive label incorporation from glutamate into ALA, using 3,4-[³H]glutamate or 1-[¹⁴C]glutamate as substrate. ALA synthase activity was indicated by RNase-insensitive incorporation of label from 2-[¹⁴C]glycine into ALA. The distribution of the two pathways among the bacteria tested was in general agreement with their previously established phylogenetic relationships and clearly indicates that the five-carbon pathway is the more ancient process, whereas the pathway utilizing ALA synthase probably evolved much later. The five-carbon pathway is apparently the more widely utilized one among bacteria, while the ALA synthase pathway seems to be limited to the subgroup of purple bacteria.Abbreviations ALA -aminolevulinic acid - DTT dithiothreitol - PALP pyridoxal phosphate - SDS sodium dodecyl sulfate - tricine N-tris-(hydroxymethyl)methylglycine     

Genes involved in the biosynthesis of PQQ fromAcinetobacter calcoaceticus

From a gene bank of theAcinetobacter calcoaceticus genome a plasmid was isolated that complements four different classes of PQQ^- mutants. Subclones of this plasmid revealed that the four corresponding PQQ genes are located on a fragment of 5 kilobases. The nucleotide sequence of this 5 kb fragment was determined and by means of Tn5 insertion mutants the reading frames of the PQQ genes could be identified. Three of the PQQ genes code for proteins of M_r 29700 (gene I), M_r 10800 (gene II) and M_r 43600 (gene III) respectively. In the DNA region where gene IV was mapped however the largest possible reading frame encodes for a polypeptide of only 24 amino acids. A possible role for this small polypeptide will be discussed. Finally we show that expression of the four PQQ genes inAcinetobacter lwoffi andEscherichia coli lead to the synthesis of the coenzyme in these organisms.     

Drosophila purine auxotrophy: New alleles ofadenosine2 exhibiting a complex visible phenotype

New mutant alleles of theadenosine2 locus (ade2; 2–17.7) have been isolated using the eye-color phenotype exhibited by the prototype auxotrophic alleleade2 ¹ as the screening criterion. The new mutants form a single complementation group, suggesting that they all exhibit purine auxotrophy and defective formylglycineamide ribotide amidotransferase enzyme, likeade2 ¹. Tests carried out on particular new alleles confirm these suggestions. The new mutants all exhibit more extreme physical defects than the prototype. They have wing abnormalities like mutants defective in pyrimidine biosynthesis and reduced bristles like those defective in protein synthesis; thus they exhibit the combined visible phenotype ofrudimentary wings,rosy eyes, andbobbed bristles. Cytogenetic analysis places the locus in the interband proximal to26B1-2.This work was supported by NSERC Operating Grant A3269 to D.N., an Alberta Heritage Foundation for Medical Research Postdoctoral Fellowship to S.Y.K.T., and National Institute on Aging Grant AG00029 to D.P.     

Regulation of pyrimidine biosynthesis in Pseudomonas cepacia

Pyrimidine biosynthesis was investigated in Pseudomonas cepacia ATCC 17759. The presence of the de novo pyrimidine biosynthetic pathway enzyme activities was confirmed in this strain. Following transposon mutagenesis of the wild-type cells, a mutant strain deficient for orotidine 5-monophosphate decarboxylase activity (pyrF) was isolated. Uracil, cytosine or uridine supported the growth of this mutant. Uracil addition to minimal medium cultures of the wild-type strain diminished the levels of the de novo pyrimidine biosynthetic enzyme activities, while pyrimidine limitation of the mutant cells increased those de novo enzyme activities measured. It was concluded that regulation of pyrimidine biosynthesis at the lelel of enzyme synthesis in P. cepacia was present. Aspartate transcarbamoylase activity was found to be regulated in the wild-type cells. Its activity was shown to be controlled in vitro by inorganic pyrophosphate, adenosine 5-triphosphate and uridine 5-phosphate.     

Poly-cis carotene pathway in the Scenedesmus mutant C-6D

The mutation of Scenedesmus obliquus strain C-6D is expressed in the dark only. Under these conditions, this strain synthesizes acyclic poly-cis carotenes. Cyclic carotenoids like -carotene or xanthophylls are absent. In the light the normal cyclic carotenes and xanthophylls are synthesized in the all-trans configuration. The poly-cis carotencs present in dark cultures have been analysed and quantitated. It could be shown that these poly-cis carotenes are identical with the poly-cis carotenes synthesized by the tomato mutant Lycopersicon esculentum var. Tangella. The poly-cis pathways, however, are different regulated in the two organisms. The tomato mutant accumulates prolycopene as the major carotene, whereas the mutant C-6D accumulates mainly pro--carotene. Furthermore, the mutation in Tangella is constitutive in light in contrast to Scenedesmus C-6D. Besides that, Scenedesmus C-6D synthesizes a further cis-carotene isomer of phytofluene as well as of -carotene. The configuration of these carotenes still have to be elucidated. The occurrence of this poly-cis carotene biosynthetic pathway by a mutation of only one enzyme, the phytoene desaturase which, however, is only expressed in darkness under heterotrophic conditions, is discussed.     

The source of gibberellins in the parthenocarpic development of ovaries on topped pea plants

The role and source of gibberellins (GAs) involved in the development of parthenocarpic fruits of Pisum sativum L. has been investigated. Gibberellins applied to the leaf adjacent to an emasculated ovary induced parthenocarpic fruit development on intact plants. The application of gibberellic acid (GA₃) had to be done within 1 d of anthesis to be fully effective and the response was concentration-dependent. Gibberellin A₁ and GA₃ worked equally well and GA₂₀ was less efficient. [³H]Gibberellin A₁ applied to the leaf accumulated in the ovary and the accumulation was related to the growth response. These experiments show that GA applied to the leaf in high enough concentration is translocated to the ovary. Emasculated ovaries on decapitated pea plants develop without application of growth hormones. When [³H] GA₁ was applied to the leaf adjacent to the ovary a substantial amount of radioactivity accumulated in the growing shoot of intact plants. In decapitated plants, however, this radioactivity was mainly found in the ovary. There it caused growth proportional to the accumulation of CA₁. Application of LAB 150978, an inhibitor of GA biosynthesis, to decapitated plants inhibited parthenocarpic fruit development and this inhibition was counteracted by the application of GA₃ (either to the fruit, or the leaf adjacent to the ovary, or through the lower cut end of the stem). All evidence taken together supports the view that parthenocarpic pea fruit development on topped plants depends on the import of gibberellins or their precursors, probably from the vegetative aerial parts of the plant.Abbreviations FW flesh weight - GA_n gibberellin A_n - HPLC high-performance liquid chromatography     

The biosynthesis and conjugation of indole-3-acetic acid in germinating seed and seedlings ofDalbergia dolichopetala

Germinating seed ofDalbergia dolichopetala converted both [²H₅]l-tryptophan and [²H₅]indole-3-ethanol to [²H₅]indole-3-acetic acid (IAA). Metabolism of [2-¹⁴C]IAA resulted in the production of indole-3-acetylaspartic acid (IAAsp), as well as several unidentified components, referred to as metabolites I, II, IV and V. Re-application of [¹⁴C]IAAsp to the germinating seed led to the accumulation of the polar, water-soluble compound, metabolite V, as the major metabolite, together with a small amount of IAA. Metabolites I, II and IV were not detected, nor were these compounds associated with the metabolism of [2-¹⁴C]IAA by shoots and excised cotyledons and roots from 26-d-oldD. dolichopetala seedlings. Both shoots and cotyledons converted IAA to IAAsp and metabolite V, while IAAsp was the only metabolite detected in extracts from excised roots. The available evidence indicates that inDalbergia, and other species, IAAsp may not act as a storage product that can be hydrolysed to provide the plant with a ready supply of IAA.Abbreviations HPLC-RC high-performance liquid chromatography-radiocounting - IAA indole-3-acetic acid - IAAsp indole-3-acetylaspartic acid - IAlnos 2-O-indole-3-acetyl-myo-inositol - IEt indole-3-ethanol     

Comparison between avian and human prolyl 4-hydroxylases: studies on the holomeric enzymes and their constituent subunits.

Prolyl 4-hydroxylase, a key enzyme in collagen biosynthesis, catalyzes the conversion of selected prolyl residues to trans-hydroxyproline in nascent or completed pro-alpha chains of procollagen. The enzyme is a tetramer composed of two nonidentical subunits, designated alpha and beta. To compare the enzyme and its subunits from different sources, the chick embryo and human placental prolyl 4-hydroxylases were purified to homogeneity and their physicochemical and immunological properties were determined. Both enzymes were glycoproteins with estimated apparent molecular weights ranging between 400 and 600 kDa. Amino acid and carbohydrate analyses showed slight differences between the two holomeric enzymes, consistent with their deduced amino acid sequences from their respective cDNAs. Human placental prolyl 4-hydroxylase contained more tightly bound iron than the chick embryo enzyme. Immunodiffusion of the human placental enzyme with antibodies raised against the purified chick embryo prolyl 4-hydroxylase demonstrated partial identity, indicating different antigenic determinants in their tertiary structures. The enzymes could be separated by high-resolution capillary electrophoresis, indicating differential charge densities for the native chick embryo and human placental proteins. Electrophoretic studies revealed that the human prolyl 4-hydroxylase is a tetrameric enzyme containing two nonidentical subunits of about 64 and 62 kDa, in a ratio of approximately 1 to 2, designated alpha and beta, respectively. In contrast, the chick embryo alpha and beta subunit ratio was 1 to 1. Notably, the human alpha subunit was partially degraded when subjected to electrophoresis under denaturing conditions. Analogously, when the chick embryo enzyme was subjected to limited proteolysis, selective degradation of the alpha subunit was observed. Finally, only the alpha subunit was bound to Concanavalin A demonstrating that the alpha subunits of prolyl 4-hydroxylase in both species were glycosylated. Using biochemical techniques, these results demonstrated that the 4-trans-hydroxy-L-proline residues in human placental collagens are synthesized by an enzyme whose primary structure and immunological properties differ from those of the previously well-characterized chick embryo enzyme, consistent with their recently deduced primary structures from cDNA sequences.