An Escherichia coli mutant producing a truncated inactive form of GlgC synthesizes glycogen: further evidences for the occurrence of various important sources of ADPglucose in enterobacteria. (17/45)

AC70R1-504 Escherichia coli mutants possess a glgC* gene with a nucleotide change resulting in a premature stop codon that renders a truncated, inactive form of GlgC. Cells over-expressing the wild type glgC, but not those over-expressing the AC70R1-504 glgC*, accumulated high ADPglucose and glycogen levels. AC70R1-504 mutants accumulated glycogen, whereas DeltaglgCAP deletion mutants lacking the whole glycogen biosynthetic machinery displayed a glycogen-less phenotype. AC70R1-504 cells with enhanced glycogen synthase activity accumulated high glycogen levels. By contrast, AC70R1-504 cells with high ADPG hydrolase activity accumulated low glycogen. These data further confirm that enterobacteria possess various sources of ADPglucose linked to glycogen biosynthesis.  (+info)

Occurrence of more than one important source of ADPglucose linked to glycogen biosynthesis in Escherichia coli and Salmonella. (18/45)

To explore the possible occurrence of sources, other than GlgC, of ADPglucose linked to bacterial glycogen biosynthesis we characterized Escherichia coli and Salmonella DeltaglgCAP deletion mutants lacking the whole glycogen biosynthetic machinery. These mutants displayed the expected glycogen-less phenotype but accumulated ADPglucose. Importantly, DeltaglgCAP cells expressing the glycogen synthase encoding glgA gene accumulated glycogen. Protein chromatographic separation of crude extracts of DeltaglgCAP mutants and subsequent activity measurement analyses revealed that these cells possess various proteins catalyzing the conversion of glucose-1-phosphate into ADPglucose. Collectively these findings show that enterobacteria possess more than one important source of ADPglucose linked to glycogen biosynthesis.  (+info)

Metabolic symbiosis and the birth of the plant kingdom. (19/45)

Eukaryotic cells are composed of a variety of membrane-bound organelles that are thought to derive from symbiotic associations involving bacteria, archaea, or other eukaryotes. In addition to acquiring the plastid, all Archaeplastida and some of their endosymbiotic derivatives can be distinguished from other organisms by the fact that they accumulate starch, a semicrystalline-storage polysaccharide distantly related to glycogen and never found elsewhere. We now provide the first evidence for the existence of starch in a particular species of single-cell diazotrophic cyanobacterium. We provide evidence for the existence in the eukaryotic host cell at the time of primary endosymbiosis of an uridine diphosphoglucose (UDP-glucose)-based pathway similar to that characterized in amoebas. Because of the monophyletic origin of plants, we can define the genetic makeup of the Archaeplastida ancestor with respect to storage polysaccharide metabolism. The most likely enzyme-partitioning scenario between the plastid's ancestor and its eukaryotic host immediately suggests the precise nature of the ancient metabolic symbiotic relationship. The latter consisted in the export of adenosine diphosphoglucose (ADP-glucose) from the cyanobiont in exchange for the import of reduced nitrogen from the host. We further speculate that the monophyletic origin of plastids may lie in an organism with close relatedness to present-day group V cyanobacteria.  (+info)

ADPG formation by the ADP-specific cleavage of sucrose-reassessment of sucrose synthase. (20/45)

The standardized enzyme coupling method for assaying sucrose synthase activities in the direction of sucrose cleavage was reexamined using enzyme preparations from cultured cells of sycamore (Acer pseudoplatanus L.) and spinach leaves (Spinacea oleracea). Both ATP and Tris, commonly utilized in assay systems to measure sucrose synthase, were found to inhibit non-competitively the ADPG-synthesizing activities of the enzyme. Upon substituting ATP by either GTP or UTP, and Tris by HEPES, we found that the sucrose synthase is capable of producing ADPG effectively, recognizing ADP as the principal substrate (Km = 5.3 microM (sycamore) and 16.8 microM (spinach]. The Vmax value for the synthesis of ADPG clearly surpasses the Vmax observed for the synthesis of UDPG by the enzyme. It was found that UDP is not inhibitory on the synthesis of ADPG by SS, which behaves allosterically with respect to the concentration level of sucrose.  (+info)

Starch metabolism in leaves. (21/45)

Starch is the most abundant storage carbohydrate produced in plants. The initiation of transitory starch synthesis and degradation in plastids depends mainly on diurnal cycle, post-translational regulation of enzyme activity and starch phosphorylation. For the proper structure of starch granule the activities of all starch synthase isoenzymes, branching enzymes and debranching enzymes are needed. The intensity of starch biosynthesis depends mainly on the activity of AGPase (adenosine 5'-diphosphate glucose pyrophosphorylase). The key enzymes in starch degradation are beta-amylase, isoamylase 3 and disproportionating enzyme. However, it should be underlined that there are some crucial differences in starch metabolism between heterotrophic and autotrophic tissues, e.g. is the ability to build multiprotein complexes responsible for biosynthesis and degradation of starch granules in chloroplasts. The observed huge progress in understanding of starch metabolism was possible mainly due to analyses of the complete Arabidopsis and rice genomes and of numerous mutants with altered starch metabolism in leaves. The aim of this paper is to review current knowledge on transient starch metabolism in higher plants.  (+info)

Comparative analysis of mitochondrial and amyloplast adenylate translocators. (22/45)

Structurally intact and metabolically competent mitochondria isolated from liquid-culture cells of sycamore (Acer pseudoplatanus L.) were shown to incorporate ADPglucose. Employing the double silicone oil layer filtering centrifugation method, we examined the kinetic properties of the uptake of various adenylates as well as the inhibitory effects exerted by carboxyatractyloside, atractyloside and bongkrekic acid, known specific inhibitors of the mitochondrial adenylate translocator. Immunoblot patterns of peptides derived from the partial proteolytic digestion of the mitochondrial and plastid adenylate translocators were shown to be essentially the same. We conclude that the molecular entities engaged in the adenylate transport system operating in two different organelles, mitochondria and amyloplasts, are very similar.  (+info)

The crystal structures of the open and catalytically competent closed conformation of Escherichia coli glycogen synthase. (23/45)

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Phylogenetic and biochemical evidence supports the recruitment of an ADP-glucose translocator for the export of photosynthate during plastid endosymbiosis. (24/45)

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