Linked Life Data

240834

Source:http://linkedlifedata.com/resource/pubmed/id/240834

Statements in which the resource exists as a subject.
PredicateObject
rdf:type
lifeskim:mentions
pubmed:issue
19
pubmed:dateCreated
1975-12-23
pubmed:abstractText
An Escherichia coli B mutant, SG14, accumulates glycogen at 28% the rate observed for the parent E. coli B strain. The glycogen accumulated in the mutant is similar to the glycogen isolated from the parent strain with respect to alpha- and beta-amylosis, chain length determination, and I2-complex absorption spectra. The SG14 mutant contains normal glycogen synthase and branching enzyme activity but has an ADP-glucose pyrophosphorylase with altered kinetic and allosteric properties. The mutant enzyme has been partially purified and requires a 12-fold higher concentration of fructose-P2 or a 26 fold higher concentration of pyridoxal-P than the parent type enzyme for 50% of maximal allosteric activation. TPNH, an effective activator of the E. coli B enzyme, does not activate the SG14 ADP-glucose pyrophosphorylase. Other studies show that for the SG14 enzyme the concentrations of ATP and Mg2+ in the synthesis direction and the concentrations of ADP-glucose and PPi in the pyrophosphorolysis direction required to give 50% of maximal activity are 3- to 6-fold higher than those observed for the parent E. coli B ADP-glucose pyrophosphorylase. The Km for alpha-glucose-1-P at saturating to half-saturating concentrations of the activator, fructose-P2, are about the same for both enzymes. However, in the presence of no activator, the concentration of glucose-1-P required for half-maximal activity is about 1.8-fold higher for the SG14 enzyme. Thus SG14 ADP-glucose pyrophosphorylase has lower affinity for its substrates than does the parent enzyme. Previously the SG14 enzyme had been shown to be less sensitive to inhibition by 5'-AMP than the E. coli B enzyme. This ensensitivity to inhibition renders the SG14 enzyme less responsive to energy charge than the E. coli B ADP-glucose pyrophosphorylase. On the basis of the above results and taking into account the reported concentrations of fructose-P2, of pyridoxal-P, and of the adenine nucleotide pool and its energy charge in E. coli strains, it is concluded that furctose-P2 is the important physiological allosteric activator of E. coli ADP-glucose pyrophosphorylase. Furthermore, the 1.7-fold increased rate of accumulation of glycogen observed when E. coli B or SG14 shifts from exponential phase to stationary phase of growth in nitrogen-limiting media can be accounted for by the 2.4-fold increase of the levels of the glycogen biosynthetic enzymes, glycogen synthase, and ADP-glucose pyrophosphorylase. Thus both allosteric regulation of the ADP-glucose pyrophosphorylase as well as the genetic regulation of the biosynthesis of the glycogen biosynthetic enzymes are involved in the regulation of glycogen accumulation in E. coli B.
pubmed:language
eng
pubmed:journal
pubmed:citationSubset
IM
pubmed:chemical
pubmed:status
MEDLINE
pubmed:month
Oct
pubmed:issn
0021-9258
pubmed:author
pubmed:issnType
Print
pubmed:day
10
pubmed:volume
250
pubmed:owner
NLM
pubmed:authorsComplete
Y
pubmed:pagination
7631-8
pubmed:dateRevised
2006-11-15
pubmed:meshHeading
pubmed:year
1975
pubmed:articleTitle
Biosynthesis of bacterial glycogen. Kinetic studies of a glucose-1-phosphate adenylyltransferase (EC 2.7.7.27) from a glycogen-deficient mutant of Escherichia coli B.
pubmed:publicationType
Journal Article, Research Support, U.S. Gov't, P.H.S.