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)

Yeast mutants assigned to the pet complementation group G104 were found to lack alpha-ketoglutarate dehydrogenase activity as a result of mutations in the dihydrolipoyl transsuccinylase (KE2) component of the complex. The nuclear gene KGD2, coding for yeast KE2, was cloned by transformation of E250/U6, a G104 mutant, with a yeast genomic library. Analysis of the KGD2 sequence revealed an open reading frame encoding a protein with a molecular weight of 52,375 and 42% identities to the KE2 component of Escherichia coli alpha-ketoglutarate dehydrogenase complex. Disruption of the chromosomal copy of KGD2 in a respiratory-competent haploid yeast strain elicited a growth phenotype similar to that of G104 mutants and abolished the ability to mitochondria to catalyze the reduction of NAD+ by alpha-ketoglutarate. The expression of KGD2 was transcriptionally regulated by glucose. Northern (RNA) analysis of poly(A)+ RNA indicated the existence of two KGD2 transcripts differing in length by 150 nucleotides. The concentrations of both RNAs were at least 10 times lower in glucose (repressed)- than in galactose (derepressed)-grown cells. Different 5'-flanking regions of KGD2 were fused to the lacZ gene of E. coli in episomal plasmids, and the resultant constructs were tested for expression of beta-galactosidase in wild-type yeast cells and in hap2 and hap3 mutants. Results of the lacZ fusion assays indicated that transcription of KGD2 is activated by the HAP2 and HAP3 proteins. The regulated expression of KGD2 was found to depend on sequences that map to a region 244 to 484 nucleotides upstream of the structural gene. This region contains two short sequence elements that differ by one nucleotide from the consensus core (5'-TN[A/G]TTGGT-3') that has been proposed to be essential for binding of the HAP activation complex. These data together with earlier reports on the regulation of the KGD1 and LPD1 genes for the alpha-ketoglutarate and dihydrolipoyl dehydrogenases indicate that all three enzyme components of the complex are catabolite repressed and subject to positive regulation by the HAP2 and HAP3 proteins.
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PMID:Structure and regulation of KGD2, the structural gene for yeast dihydrolipoyl transsuccinylase. 211 21

Nuclear respiratory-defective mutants of Saccharomyces cerevisiae have been screened for lesions in the mitochondrial alpha-ketoglutarate dehydrogenase complex. Strains assigned to complementation group G70 were ascertained to be deficient in enzyme activity due to mutations in the KGD1 gene coding for the alpha-ketoglutarate dehydrogenase component of the complex. The KGD1 gene has been cloned by transformation of a representative kgd1 mutant, C225/U1, with a recombinant plasmid library of wild-type yeast nuclear DNA. Transformants containing the gene on a multicopy plasmid had three- to four-times-higher alpha-ketoglutarate dehydrogenase activity than did wild-type S. cerevisiae. Substitution of the chromosomal copy of KGD1 with a disrupted allele (kgd1::URA3) induced a deficiency in alpha-ketoglutarate dehydrogenase. The sequence of the cloned region of DNA which complements kgd1 mutants was found to have an open reading frame of 3,042 nucleotides capable of coding for a protein of Mw 114,470. The encoded protein had 38% identical residues with the reported sequence of alpha-ketoglutarate dehydrogenase from Escherichia coli. Two lines of evidence indicated that transcription of KGD1 is catabolite repressed. Higher steady-state levels of KGD1 mRNA were detected in wild-type yeast grown on the nonrepressible sugar galactose than in yeast grown on high glucose. Regulation of KGD1 was also studied by fusing different 5'-flanking regions of KGD1 to the lacZ gene of E. coli and measuring the expression of beta-galactosidase in yeast. Transformants harboring a fusion of 693 nucleotides of the 5'-flanking sequence expressed 10 times more beta-galactosidase activity when grown under derepressed conditions. The response to the carbon source was reduced dramatically when the same lacZ fusion was present in a hap2 or hap3 mutant. The promoter element(s) responsible for the regulated expression of KGD1 has been mapped to the -354 to -143 region. This region contained several putative activation sites with sequences matching the core element proposed to be essential for binding of the HAP2 and HAP3 regulatory proteins.
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PMID:Structure and regulation of KGD1, the structural gene for yeast alpha-ketoglutarate dehydrogenase. 250 10

The citB of Bacillus subtilis codes for aconitase (D. W. Dingman and A. L. Sonenshein, J. Bacteriol. 169:3060-3065). By direct measurements of citB mRNA levels and by measurements of beta-galactosidase activity in a strain carrying a citB-lacZ fusion, we have examined the expression of citB during growth and sporulation. When cells were grown in nutrient broth sporulation medium, citB mRNA appeared in mid- to late-exponential phase and disappeared by the second hour of sporulation. This timing corresponded closely to the kinetics of appearance of aconitase enzyme activity. Decoyinine, a compound that induces sporulation in a defined medium, caused a rapid simultaneous increase in aconitase activity and citB transcription. After decoyinine addition, the rate of increase in aconitase activity in a 2-ketoglutarate dehydrogenase (citK) mutant and in a citrate synthase (citA) mutant was significantly less than in an isogenic wild-type strain. This is apparently due to a failure to deplete 2-ketoglutarate and accumulate citrate. These metabolites might act as negative and positive effectors of citB expression, respectively. Mutations known to block sporulation at an early stage (spo0H and spo0B) had no appreciable effect on citB expression or aconitase activity. These results suggest that appearance of aconitase is stimulated by conditions that induce sporulation but is independent of certain gene products thought to act at an early stage of sporulation.
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PMID:Relationship between aconitase gene expression and sporulation in Bacillus subtilis. 311 Jan 34

This study was aimed to evaluate the preventive role of S-allylcysteine (SAC) on mitochondrial and lysosomal enzymes in isoproterenol (ISO)-induced rats. Male albino Wistar rats were pretreated with SAC (50, 100 and 150 mg/kg) daily for a period of 45 days. After the treatment period, ISO (150 mg/kg) was subcutaneously injected to rats at an interval of 24 h for two days. The activities of heart mitochondrial enzymes (isocitrate dehydrogenase, succinate dehydrogenase, malate dehydrogenase and alpha-ketoglutarate dehydrogenase) and respiratory chain enzymes (NADH dehydrogenase and cytochrome C oxidase) were decreased significantly (p<0.05) in ISO-induced rats. The activities of lysosomal enzymes (beta-glucuronidase, beta-N-acetyl glucosaminidase, beta-galactosidase, cathepsin-D and acid phosphatase) were increased significantly (p<0.05) in serum and heart of ISO-induced rats. Pretreatment with SAC (100 mg/kg and 150 mg/kg) for a period of 45 days increased significantly (p<0.05) the activities of mitochondrial and respiratory chain enzymes and decreased the activities of lysosomal enzymes significantly (p<0.05) in ISO-induced rats. Oral administration of SAC (50, 100 and 150 mg/kg) for a period of 45 days to normal rats did not show any significant (p<0.05) effect in all the parameters studied. The altered electrocardiogram (ECG) of ISO-treated rats was also restored to near normal by treatment with SAC (100 and 150 mg/kg). These results confirm the efficacy of SAC in alleviating ISO-induced cardiac damage.
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PMID:S-allylcysteine ameliorates isoproterenol-induced cardiac toxicity in rats by stabilizing cardiac mitochondrial and lysosomal enzymes. 1718 65