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

We have previously demonstrated the existence of two types of endopeptidase in Escherichia coli. A purification procedure is described for one of these, designated protease II. It has been purified about 13,500-fold with a recovery of 24%. The isolated enzyme appears homogeneous by electrophoresis and gel filtration. Its molecular weight is estimated by three different methods to be about 58,000. Its optimal pH is around 8. Protease II activity is unaffected by chelating agents and sulfhydryl reagents. Amidase and proteolytic activities are stimulated by calcium ion, which decreases the enzyme stability. Like pancreatic trypsin, this endopeptidase catalyses the hydrolysis of alpha-amino-substituted lysine and arginine esters. It appears distinct from the previously isolated protease I, which is a chymotrypsin-like enzyme. The apparent Michaelis constant for hydrolysis of N-benzoyl-L-arginine ethyl ester is 4.7 X 10(-4) M. The esterase activity is inhibited by diisopryopylphosphorofluoridate (Ki(app) equals 2.7 X 10(-3) M) and tosyl lysine chloromethyl ketone (Ki(app) equals 1.8 X 10(-5) M), indicating that serine and histidine residues may be present in the active site. However, protease II is insensitive to phenylmethanesulfonyl fluoride and several natural trypsin inhibitors. Its amidase and esterase activities are competitively inhibited by free arginine and aromatic amidines. The proteolytic activity measured on axocasein is very low. In contrast to trypsin, protease II is without effect on native beta-galactosidase. It easily degrades aspartokinase I and III. Nevertheless both enzymes are resistant to proteolysis in the presence of their respective allosteric effectors. These results provide further evidence that such differences in protease susceptibility can be related to the conformational state of the substrate. The possible implication of structural changes in the mechanism of preferential proteolysis in vivo, is discussed.
 ...
PMID:Protease II from Escherichia coli. Purification and characterization. 24 Aug 39

Recent genetic mapping of the aspartokinase II (lysC) operon of Bacillus subtilis [M. Petricek. L. Rutberg & L. Hederstedt (1989) FEMS Microbiology Letters 61, 85-88; N.Y. Chen. J. J. Zhang & H. Paulus (1989) Journal of General Microbiology 135, 2931-2940] has shown its chromosomal location to be close to the aecA locus, the mutation of which leads to highly increased levels of aspartokinase II. In order to examine the relationship between lysC and aecA, we have cloned the control regions of the lysC operon from several independent aecA mutants and determined their nucleotide sequences. The nucleotide sequences of the aecA mutants differed from the wild-type sequence by the substitution of one or two nucleotides at two widely separated sites in the transcribed leader region of the lysC operon. To confirm that the observed nucleotide changes are indeed responsible for the AecA phenotype and not simply the reflection of sequence polymorphisms in different B. subtilis strains, we introduced the same nucleotide substitutions as those observed in the aecA strains into the leader region of the wild-type lysC operon by oligonucleotide-directed mutagenesis. The expression of the mutagenized genes was analysed after transcriptional or translational fusion to lacZ in a single-copy integration vector. The levels of beta-galactosidase were greatly elevated by the nucleotide substitutions, with similar increases observed in transcriptional and translational fusions. The high level of expression of beta-galactosidase in the lysC'-lac'Z strains with nucleotide substitutions corresponding to the aecA mutations was resistant to repression by L-lysine but was completely abolished by the inactivation of the lysC promoter.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Identification of aecA mutations in Bacillus subtilis as nucleotide substitutions in the untranslated leader region of the aspartokinase II operon. 190 38

Mutants containing fusions of the lac gene to the lysC gene were isolated. In these, the expression of beta-galactosidase was regulated by lysine (and arginine), as previously described for aspartokinase III.
 ...
PMID:Regulation of aspartokinase III synthesis in Escherichia coli: isolation of mutants containing lysC-lac fusions. 624 91