Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:3.2.1.23 (beta-galactosidase)
 14,648 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Centrifugation of homogenates of bovine retinas to isopycnic equilibrium in sucrose density gradients yielded three partially overlapping bands of particles which were, in the order of increasing density: (a) photoreceptor cell (rod) outer segments; (b) plasma membranes, lysosomes, and large fragments of endoplasmic reticulum; and (c) mitochondria. The only enzyme activity investigated which had a peak coinciding only with outer segment fractions was guanylate cyclase. Enzyme activities with peaks in both the outer segment and denser fractions included 5'-nucleotidase and cyclic GMP phosphodiesterase. Enzyme activities with peaks only in the denser fractions included sodium and potassium ion-activated ATPase ((Na+ + K+)-ATPase), adenylate cyclase, cyclic AMP phosphodiesterase, beta-glucosidase, beta-galactosidase, and succinate-dependent cytochrome c reductase. These results suggest that some of the activities once thought to be present in rod outer segments are actually present in particles from elsewhere in the retina which contaminate rod outer segment preparations.
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PMID:Distribution of enzyme activities in subcellular fractions of bovine retina. 0 65

Synthesis of catabolite-sensitive enzymes is repressed in mutants defective in the general proteins (enzyme I and HPr) of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system (ptsI and ptsH mutations). To elucidate the mechanism of this phenomenon we constructed isogenic strains carrying pts mutations as well as different lesions of regulation of the lac operon or mutations affecting adenylate cyclase activity (cya mutation) and synthesis of cyclic AMP-receptor protein (crp mutation) Measurements of the differential rate of beta-galactosidase synthesis in these strains showed that the repressive effect of pts mutations was revealed in lac+, lacI, lacOc and cya bacteria, but it was lost in lacP and crp strains. It was concluded that mutational damage to the general components of the phosphoenolpyruvate-dependent phosphotransferase system diminishes activity of the lac promoter. The results obtained led to the conclusion that pts gene products (apparently phospho approximately HPr) are necessary for the initiation of transcription of catabolite-sensitive operons in E. coli.
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PMID:Involvement of the Escherichia coli phosphoenolpyruvate-dependent phosphotransferase system in regulation of transcription of catabolic genes. 10 72

In this study we have tried to answer the following questions: (1) is it possible for different catabolite-repressible genes, although submitted to the same control, to be expressed selectively depending upon the growth conditions, and (2) what is the effect of increasing the osmolarity of the medium on the intracellular level of cAMP? Two conditions were found to cause a continuous variation of intracellular cAMP levels during growth. With different strains, higher cAMP levels are required for induction of the tryptophanase gene than one required for induction of the lactose operon. cAMP has been provided externally in adenyl cyclase minus cells of a mutant that has been made permeable by EDTA treatment. Although external cAMP concentrations, 10 times higher than the usual intracellular levels, are required for induction of beta-galactosidase and tryptophanase, the difference of requirements of cAMP is maintained. An increase in the osmolarity of the medium by sucrose addition causes a fourfold decrease in the intracellular cAMP level. As a consequence this prevents the induction of tryptophanase whereas beta-galactosidase is still inducible. After pulse induction, a difference in the kinetics of expression of the tryptophanase and beta-galactosidase genes was found. Its relationship with the previous results is discussed.
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PMID:Different cyclic adenosine 3',5'-monophosphate requirements for induction of beta-galactosidase and tryptophanase. Effect of osmotic pressure on intracellular cyclic adenosine 3,5-monophosphate concentrations. 16 97

1. The effect of carbon source variation in bacterial growth media on their growth rate, inducible enzyme and cyclic AMP synthesis was examined: an inverse relationship between the culture's growth rate and its differential rate of inducible enzyme (tryptophanase and beta-galactosidase), and cyclic AMP synthesis was found. 2. The effect of the culture's growth phase on its sensitivity or resistance to glucose catabolite repression was determined in the wild type and a catabolite insensitive mutant (ABDROI): the wild type's sensitivity to glucose repression was not affected, whereas the insensitivity of the mutant was found to be limited to its early logarithmic phase of growth. At late log, or stationary phase, the mutant was found to be sensitive to glucose repression. 3. Examination of the kinetics of glucose uptake by the mutant, using alpha-[1 4-C] methyl-glucoside showed evidence for two transport systems each with a different affinity to glucose. A low affinity transport system (apparent Km of 3.4-10-minus 5 M) which appears mostly at the early logarithmic phase of growth. A high affinity transport system (apparent Km of 1.2-10-minus 5 M) which appears mostly at the late log and stationary phases of growth. 4. The effect of the culture density variation on its sensitivity to glucose repression showed that sensitivity to glucose catabolic repression is primarily a reflection of the formation of an allosteric effector molecule between glucose and its specific transport molecule which in turn regulates the activity of the adenylate cyclase.
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PMID:On the regulation of adenosine 3', 5'-monophosphate synthesis in bacteria. I. Effect of carbon source variation on cyclic AMP synthesis in Escherichia coli B/r. 16 29

Adenine requiring mutants of Serratia marcescens SM-6-F'lac+ have been found to grow well in minimal-glucose medium solely supplemented with cAMP. From one of these ade strains double mutants (called ade cpd) were isolated which could no longer utilize cAMP but which still grew on 5'AMP. Dialyzed cell extracts (soluble fraction) of the double mutants, assayed for cAMP phosphodiesterase, were unable to hydrolyze cAMP whereas cell extracts of the parental strains yielded 5'AMP at a rate of 1.6-2.0 mumoles min-1 mg-1 protein. The loss of the phosphodiesterase activity in S. marcescens cpd W 1181 did not cause an accumulation of large amounts of cAMP as was found for the diesterase-negative mutant AB257pc-1 of Escherichia coli. The induced synthesis of beta-galactosidase in mutant cpd W 1181 showed about the same sensitivity to transient and permanent catabolite (glucose) repression as the corresponding cpd+ strain. Starting from S. marcescens cpd W 1182 three independent double mutants (called cpd cya) were isolated which required exogenous cAMP for utilizing various carbohydrates as carbon source, for motility and for the formation of extracellular lipase and the red pigment prodigiosine. The intracellular concentration of cAMP in these mutants, grown in nutrient broth, was 40-60% of that of the parental strain which is about 4 x 10(-4) M. However, the adenylate cyclase in cell extracts of the mutants W 1237 and W 1270 was like that of the corresponding cya+ strain (about 2 x 10(-2) mumoles min-1 mg-1 protein).
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PMID:Mutants of Serratia marcescens lacking cyclic nucleotide phosphodiesterase activity and requiring cyclic 3',5'-AMP for the utilization of various carbohydrates. 16 32

Two mutants are described in which the synthesis of tryptophanase is unusually insensitive to catabolite repression. Neither mutation is linked by transduction to the tryptophane structural gene, neither mutation renders the synthesis of beta-galactosidase insensitive to catabolite repression, and the mutations do not permit tryptophanase to be synthesized in strains deficient in adenyl cyclase. During growth in glucose-minimal medium the mutants maintained a similar intracellular concentration of cyclic AMP to their wild-type parent; but since in the wild type the concentration of cyclic AMP was the same in glycerol-minimal medium as in glucose-minimal medium, it is doubtful whether catabolite repression is mediated by measurable changes in the concentration of this nucleotide.
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PMID:Mutations in Escherichia coli that relieve catabolite repression of tryptophanase synthesis. Mutations distant from the tryptophanase gene. 17 93

The regulation of catabolite repression of beta-galactosidase has been studied in Escherichia coli mutants deleted for the adenyl cyclase gene (cya delta), and thus unable to synthesize cyclic AMP. It has been found that, provided a second mutation occurs either in the crp gene coding for the catabolite gene activator protein (CAP) or in the Lactose region, these mutants exhibit catabolite repression. If the catabolite repression seen in the mutant strains corresponds to the mechanism operating in wild-type cells the results would suggest that the intracellular concentration of cyclic AMP cannot be the unique regulator of catabolite repression.
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PMID:Catabolite repression in Escherichia coli mutants lacking cyclic AMP. 20 9

Iron controls luminescence in Vibrio fischeri by an indirect but undefined mechanism. To gain insight into that mechanism, the involvement of cyclic AMP (cAMP) and cAMP receptor protein (CRP) and of modulation of DNA levels in iron control of luminescence were examined in V. fischeri and in Escherichia coli containing the cloned V. fischeri lux genes on plasmids. For V. fischeri and E. coli adenylate cyclase (cya) and CRP (crp) mutants containing intact lux genes (luxR luxICDABEG), presence of the iron chelator ethylenediamine-di(o-hydroxyphenyl acetic acid) (EDDHA) increased expression of the luminescence system like in the parent strains only in the cya mutants in the presence of added cAMP. In the E. coli strains containing a plasmid with a Mu dl(lacZ) fusion in luxR, levels of beta-galactosidase activity (expression from the luxR promoter) and luciferase activity (expression from the lux operon promoter) were both 2-3-fold higher in the presence of EDDHA in the parent strain, and for the mutants this response to EDDHA was observed only in the cya mutant in the presence of added cAMP. Therefore, cAMP and CRP are required for the iron restriction effect on luminescence, and their involvement in iron control apparently is distinct from the known differential control of transcription from the luxR and luxICDABEG promoters by cAMP-CRP. Furthermore, plasmid and chromosomal DNA levels were higher in E. coli and V. fischeri in the presence of EDDHA. The higher DNA levels correlated with an increase in expression of chromosomally encoded beta-galactosidase in E. coli and with a higher level of autoinducer in cultures of V. fischeri. These results implicate cAMP-CRP and modulation of DNA levels in the mechanism of iron control of the V. fischeri luminescence system.
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PMID:Mechanism for iron control of the Vibrio fischeri luminescence system: involvement of cyclic AMP and cyclic AMP receptor protein and modulation of DNA level. 132 97

A gene from Rhizobium meliloti coding for an adenylate cyclase was sequenced, and the deduced protein sequence was compared with those of other known adenylate cyclases. No similarity could be detected with the procaryotic counterparts. However, striking similarity was found with the catalytic region of Saccharomyces cerevisiae adenylate cyclase, the cytoplasmic domains of bovine adenylate cyclase, and two mammalian guanylate cyclases. The gene was fused to the enteric beta-galactosidase, and the chimeric protein was purified by affinity chromatography. This fusion protein was found to direct the synthesis of cyclic AMP in vitro. This activity was strongly inhibited by the presence of GTP, but no cyclic GMP synthesis could be detected in conditions permitting cyclic AMP synthesis.
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PMID:Rhizobium meliloti adenylate cyclase is related to eucaryotic adenylate and guanylate cyclases. 197 May 65

Mutants of Salmonella typhimurium defective in the proteins of the fructose operon [fruB(MH)KA], the fructose repressor (fruR), the energy-coupling enzymes of the phosphoenolpyruvate:sugar phosphotransferase system (PTS) (ptsH and ptsI), and the proteins of cyclic AMP action (cya and crp) were analyzed for their effects on cellular physiological processes and expression of the fructose operon. The fru operon consists of three structural genes: fruB(MH), which encodes the enzyme IIIFru-modulator-FPr tridomain fusion protein of the PTS; fruK, which encodes fructose-1-phosphate kinase; and fruA, which encodes enzyme IIFru of the PTS. Among the mutants analyzed were Tn10 insertion mutants and lacZ transcriptional fusion mutants. It was found that whereas a fruR::Tn10 insertion mutant, several fruB(MH)::Mu dJ and fruK::Mu dJ fusion mutants, and several ptsHI deletion mutants expressed the fru operon and beta-galactosidase at high constitutive levels, ptsH point mutants and fruA::Mu dJ fusion mutants retained inducibility. Inclusion of the wild-type fru operon in trans did not restore fructose-inducible beta-galactosidase expression in the fru::Mu dJ fusion mutants. cya and crp mutants exhibited reduced basal activities of all fru regulon enzymes, but inducibility was not impaired. Surprisingly, fruB::Mu dJ crp or cya double mutants showed over 10-fold inducibility of the depressed beta-galactosidase activity upon addition of fructose, even though this activity in the fruB::Mu dJ fusion mutants that contained the wild-type cya and crp alleles was only slightly inducible. By contrast, beta-galactosidase activity in a fruK::Mu dJ fusion mutant, which was similarly depressed by introduction of a crp or cya mutation, remained constitutive. Other experiments indicated that sugar uptake via the PTS can utilize either FPr-P or HPr-P as the phosphoryl donor, but that FPr is preferred for fructose uptake whereas HPr is preferred for uptake of the other sugars. Double mutants lacking both proteins were negative for the utilization of all sugar substrates of the PTS, were negative for the utilization of several gluconeogenic carbon sources, exhibited greatly reduced adenylate cyclase activity, and were largely nonmotile. These phenotypic properties are more extreme than those observed for tight ptsH and ptsI mutants, including mutants deleted for these genes. A biochemical explanation for this fact is proposed.
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PMID:Physiological consequences of the complete loss of phosphoryl-transfer proteins HPr and FPr of the phosphoenolpyruvate:sugar phosphotransferase system and analysis of fructose (fru) operon expression in Salmonella typhimurium. 220 52


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