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L Bock

Publications and source records attributed to L Bock.

9 recordsLinked to original sources
PubMed1990

Improved methods for the purification of enzymes of the folate pathway in Escherichia coli. I. Chromatographic methods.

A sequence of chromatographic procedures is described for the isolation of three consecutive enzymes of the folate pathway in Escherichia coli: hydroxymethyldihydropteridine pyrophosphokinase (E.C. 2.7.6.3) (I), 7,8-dihydropteroate synthase (E.C. 2.5.1.15) (II) and 7,8-dihydrofolate reductase, (E.C. 1.5.1.3) (III). Starting with the crude extract, ion-exchange chromatography on a DEAE-Sepharose CL-6B column with a salt gradient completely separated I, II and III. I and II were further purified by hydrophobic-interaction chromatography on Phenyl-Sepharose CL-4B, followed by size-exclusion chromatography on Ultrogel AcA 54. For III only size-exclusion chromatography was used. The overall enrichment factors, on the basis of protein, were 13,700-fold for I, 280-fold for II and 500-fold for III. Bacterial batches of more than 500 g were handled.

Chromatography, Ion Exchange↗
PubMed1990

[Mourning].

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Adaptation, Psychological↗
PubMed1985

Human pancreatic growth hormone releasing factor (hpGRF): GRF- and GH-levels after bolus injection and infusion of hpGRF.

Synthetic human pancreatic growth hormone releasing factor (hpGRF) was given as an i.v. bolus to healthy volunteers in 5 different dosages (3.3 micrograms to 200 micrograms hpGRF). In addition 11 healthy subjects were infused over 2 respectively 5 hours in a dosage of 100 micrograms hpGRF/h after receiving a bolus of 50 micrograms hpGRF. Four healthy subjects served as placebo controls. GH, PRL, TSH, and GRF were measured by specific radioimmunoassays. The results show the clearcut dose response relationship between the administered GRF dosage and the resulting GH response from 3.3 to 50 micrograms hpGRF i.v. Higher dosages of hpGRF did not lead to a more pronounced GH response though there was a linear dose response relationship between the administered hpGRF and the GRF immunoreactivity 5 minutes after injection. Infusion of hpGRF could not sustain elevated GRF levels and a second bolus of 50 micrograms hpGRF given at the end of the 2-respectively 5-hour infusion led to a minor increase compared to the first bolus. 100 micrograms hpGRF was given to 14 patients with active acromegaly leading to a significant rise of the GH levels with the exception of 3 patients. Of the latter 3 two had received previous therapy, and one patient suffered from ectopic GRF hypersecretion. When GH responses to hpGRF were compared to the responses to other releasing hormones there was no correlation. After transsphenoidal surgery divergent responses of GH were seen. In one patient with low basal GH and an exaggerated rise after GRF before surgery there was no response after successful transsphenoidal operation.(ABSTRACT TRUNCATED AT 250 WORDS)

Acromegaly↗
PubMed1977

Purification and characterization of the DNA-dependent RNA polymerase and its subunit sigma from Micrococcus luteus.

DNA-dependent RNA polymerase from Micrococcus luteus can be isolated from cell extracts after removal of an excess of nucleic acids by fractionation with ammonium sulfate, followed by two consecutive gel filtrations through agarose and chromatography on cellulose phospate. Either homogeneous holoenzyme or a mixture of core and holoenzyme is obtained in this way, as is indicated by electrophoresis in polyacrylamide gels in the absence of detergent, where core enzyme migrates ahead of holoenzyme. Homogeneous core enzyme can be isolated from holoenzyme by chromatography on DEAE-cellulose. Core enzyme contains the subunits alpha, beta and beta' previously described [U.I. Lill et al., (1975) Eur. J. Biochem. 52, 411-420] in a molar ratio of 2:1:1. Holoenzyme contains an additional subunit sigma of 80 000 molecular weight (molar subunit composition alpha2 betabeta' sigma) and two relatively small polypeptides (molecular weight 14 000 and 25 000, respectively). Subunit sigma may be isolated from holoenzyme by chromatography on DEAE-cellulose at pH 6.9 in the presence of low concentrations of glycerol. The behaviour of holoenzyme during sedimentation in a glycerol gradient at low ionic strength indicates its occurrence as a dimer of the alpha2betabeta'sigma-protomer, whereas the monomeric form is preferred by core enzyme. Holoenzyme is much more active than core enzyme in RNA synthesis on bacteriophage T4DNA as template. The activity of the latter is stimulated by isolated sigma. M. luteus sigma as well as holoenzyme enhances also the activity of core enzyme fro- Escherichia coli. The formation of a hybrid between micrococcal sigma and E. coli core polymerase is also suggested by the influence of sigma on the oligomerisation of the enzyme from E. coli.

DNA, Viral↗