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)

Under diazotrophic conditions in the absence of molybdenum (Mo) and vanadium (V), Azotobacter vinelandii reduces N2 to NH4+ by using nitrogenase 3 (encoded by anfHDGK). However, dinitrogenase reductase 2 (encoded by vnfH) is also expressed under these conditions even though this protein is a component of the V-containing alternative nitrogenase. Mutant strains that lack dinitrogenase reductase 2 (VnfH-) grow slower than the wild-type strain in N-free, Mo-, and V-deficient medium. In this medium, these strains synthesize dinitrogenase reductase 1 (a component of the Mo-containing nitrogenase encoded by nifH), even though this component is not normally synthesized in the absence of Mo. Strains that lack both dinitrogenase reductases 1 and 2 (NifH-VnfH-) are unable to grow diazotrophically in Mo- and V-deficient medium. In this medium, NifH- VnfH- strains containing an anfH-lacZ transcriptional fusion exhibited less than 3% of the beta-galactosidase activity observed in the wild type with the same fusion. Beta-Galactosidase activity expressed by VnfH- mutants containing the anfH-lacZ fusion ranged between 57 and 78% of that expressed by the wild type containing the same fusion. Thus, expression of dinitrogenase reductase 2 seems to be required for transcription of the anfHDGK operon, although, in VnfH-mutants, dinitrogenase reductase 1 appears to serve this function. Active dinitrogenase reductase 1 or 2 is probably required for this function since a nifM deletion mutant containing the anfH-lacZ fusion was unable to synthesize beta-galactosidase above background levels. An anfA deletion strain containing the anfH-lacZ fusion exhibited beta-galactosidase activity at 16% of that of the wild type containing the same fusion. However, in the presence of NH4+, the beta-galactosidase activity expressed by this strain more than doubled. This indicates that AnfA is required not only for normal levels of anfHDGK transcription but also for NH4+ -and, to a lesser extent, Mo-mediated repression of this transcription.
 ...
PMID:The gene encoding dinitrogenase reductase 2 is required for expression of the second alternative nitrogenase from Azotobacter vinelandii. 190 63

The chlA locus encodes functions required for the biosynthesis of the molybdopterin part of the molybdenum cofactor. Mutants, carrying gene fusions at the chlA locus, which place beta-galactosidase expression under the control of the chlA promoter, have been isolated employing lambda placMu1 as the mutagen. The mutants exhibited beta-galactosidase expression which was greatly enhanced when grown anaerobically. Secondary mutations at the chlB, D, E or G loci did not affect the high level of expression. The fnr gene product was not required for the anaerobic expression. Bacteriophage lambda transducing phages were isolated which carried the phi(chlA-lac) mutations and were used to construct chlA+/phi(clA-lac) merodiploids. The merodiploids exhibited a much lower level of expression but showed the same characteristics as strains carrying lac fusions to the single chromosomal chlA locus. Genetic evidence is presented which strongly suggests that the molybdenum cofactor is a repressor of chlA expression. The anaerobic enhancement of chlA expression is mediated via a mechanism that is distinct from the molybdenum cofactor effect.
 ...
PMID:Regulation of the chlA locus of Escherichia coli K12: involvement of molybdenum cofactor. 190 67

The nifBQ transcriptional unit of Azotobacter vinelandii has been previously shown to be required for activity of the three nitrogenase systems, Mo nitrogenase, V nitrogenase, and Fe nitrogenase, present in this organism. We studied regulation of expression and the role of the nifBQ region by means of translational beta-galactosidase fusions to each of the five open reading frames: nifB, orf2 (fdxN), orf3 (nifO), nifQ, and orf5. Expression of the first three open reading frames was observed under all three diazotrophic conditions; expression of orf5 was never observed. Genes nifB and fdxN were expressed at similar levels. With Mo, expression of nifO and nifQ was approximately 20- and approximately 400-fold lower than that of fdxN, respectively. Without Mo, expression of nifB dropped three- to fourfold and that of nifQ dropped to the detection limit. However, expression of nifO increased threefold. The products of nifB, fdxN, nifO, and nifQ have been visualized in A. vinelandii as beta-galactosidase fusion proteins with the expected molecular masses. The NifB- fusion lacked activity for any of the three nitrogenase systems and showed an iron-molybdenum cofactor-deficient phenotype in the presence of Mo. The FdxN- mutation resulted in reduced nitrogenase activities, especially when V was present. Dinitrogenase activity in extracts was similarly affected, suggesting a role of FdxN in iron-molybdenum cofactor synthesis. The NifO(-)-producing mutation did not affect any of the nitrogenases under standard diazotrophic conditions. The NifQ(-)-producing mutation resulted in an increased (approximately 1,000-fold) Mo requirement for Mo nitrogenase activity, a phenotype already observed with Klebsiella pneumoniae. No effect of the NifQ(-)-producing mutation on V or Fe nitrogenase was found; this is consistent with its very low expression under those conditions. Mutations in orf5 had no effect on nitrogenase activity.
 ...
PMID:Expression of the nifBfdxNnifOQ region of Azotobacter vinelandii and its role in nitrogenase activity. 849 13

Azotobacter is a diazotrophic bacterium that harbors three genetically distinct nitrogenases referred to as nif, vnf, and anf systems. The nifM is an accessory gene located in the nif gene cluster and is transcriptionally regulated by the NifA. However, Azotobacter mutants that lack NifA are known to synthesize functional NifM and this accessory protein is known to be needed for the activity of nitrogenase-2 and nitrogenase-3. To determine how the transcription of nifM is regulated when Azotobacter is grown under conditions in which nitrogenase-2 or nitrogenase-3 is expressed, we generated an Azotobacter vinelandii strain that carries a nifM:lacZ-kanamycin resistance gene cassette in its chromosome. In this strain the nifM open reading frame was disrupted by the presence of a lacZ-kanamycin resistance gene cassette so that it could not produce active NifM. Moreover, the lacZ gene was placed under the transcriptional control elements of the nifM gene so that the lacZ expression could be used as a marker to determine the extent of expression of the nifM gene under different growth conditions. Our results show that this strain was unable to grow in Burk's nitrogen-free medium supplemented with either molybdenum or vanadium or lacking both metals suggesting that in the absence of functional NifM none of the nitrogenases were active. It was also found that the nifM expression was differentially regulated when the A. vinelandii cells were grown under conditions that activate nitrogenase-2 and nitrogenase-3, as determined by liquid beta-galactosidase activity measurements. These results suggest that the transcriptional activators, VnfA and AnfA, may regulate the nifM expression.
 ...
PMID:Regulated expression of the nifM of Azotobacter vinelandii in response to molybdenum and vanadium supplements in Burk's nitrogen-free growth medium. 1052 62

Culture growth and recombinant protein yield of the Pichia pastoris GS115 methanol utilization positive system were studied in response to the types and levels of metals present in the growth medium and the supplemental salts typically used for these fermentations. Magnesium and zinc were both required to support cell growth but at significantly reduced levels compared to the control. However, supplementation with calcium, cobalt, iron, manganese, iodine, boron, and molybdenum were not required to sustain cell mass. When the medium was reformulated with only zinc and magnesium, the cells grew to 12-15 generations, which are expected for high cell density fed-batch fermentations. Product yields of the recombinant protein beta-galactosidase were significantly influenced by the trace metal concentrations. By using response surface and full factorial designs, maximum protein yield occurred when the concentration of zinc salt was limited to the level necessary only to support cell mass while protein yield positively correlated to increasing levels of the remaining trace metal salts. These studies are the first to show that excess trace metals must be optimized when developing P. pastoris based fed-batch fermentations.
 ...
PMID:Evaluation of metals in a defined medium for Pichia pastoris expressing recombinant beta-galactosidase. 1739 84