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L Kerscher

Publications and source records attributed to L Kerscher.

10 recordsLinked to original sources
PubMed1985

Preliminary X-ray diffraction studies on a ferredoxin from the thermophilic archaebacterium, Thermoplasma acidophilum.

A ferredoxin from the thermophilic archaebacterium, Thermoplasma acidophilum, is supposed to contain two (4Fe-4S) active centers; one center could be linked by four cysteine residues to the protein and the other bonded with three cysteines and an unknown group. This ferredoxin has been crystallized by salting-out against 2.3 M-ammonium sulfate solution. The space group is P21212 with cell dimensions of a = 59.20 A, b = 52.77 A and c = 41.28 A. Four molecules pack in the unit cell with Vm = 2.03 A3/dalton.

Amino Acid Sequence↗
PubMed1985

Precipitation methods for the determination of LDL-cholesterol.

The selective precipitation of low-density lipoproteins (LDL) with polyvinyl sulfate (PVS), and the immunoprecipitation of high-density lipoproteins (HDL) and very-low-density lipoproteins (VLDL) with an anti-HDL antibody, can both be used to establish simple methods for the determination of LDL cholesterol. Whereas the PVS method requires the calculation of LDL cholesterol as the difference of total and supernatant cholesterol, the immunoprecipitation method allows the direct measurement of LDL cholesterol in the supernatant. As a first step, both methods were optimized to yield accurate values for normolipemic and slightly hyperlipemic serum samples. Moreover, the determination of LDL-cholesterol in lipemic sera can be achieved by a combination of immunoprecipitation and polyanion precipitation.

Chemical Precipitation↗
PubMed1985

Amino acid sequence of a ferredoxin from thermoacidophilic archaebacterium, Sulfolobus acidocaldarius. Presence of an N6-monomethyllysine and phyletic consideration of archaebacteria.

The amino acid sequence of a ferredoxin from a thermoacidophilic archaebacterium, Sulfolobus acidocaldarius, was determined by a combination of various conventional methods to be as follows: Gly-Ile-Asp-Pro-Tyr-Arg-Thr-His-Lys-Pro-Val-Val-Gly-Asp-Ser-Ser-Gly-His- Lys-Ile -Tyr-Gly-Pro-Val-Glu-Ser-Pro-Lys(Me)-Val-Leu-Gly-Val-His-Gly-Thr-Ile-Val -Gly-Va l-Asp-Phe-Asp-Leu-Cys-Ile-Ala-Asp-Gly-Ser-Cys-Ile-Thr-Ala-Cys-Pro-Val-As n-Val-P he-Gln-Trp-Tyr-Glu-Thr-Pro-Gly-His-Pro-Ala-Ser-Glu-Lys-Lys-Ala-Asp-Pro-V al-Asn- Glu-Gln-Ala-Cys-Ile-Phe-Cys-Met-Ala-Cys-Val-Asn-Val-Cys-Pro-Val-Ala-Ala- Ile-Asp -Val-Lys-Pro-Pro. It was composed of 103 amino acid residues giving a molecular weight of 10,908 excluding Fe and S atoms. This ferredoxin contained an N6-monomethyllysine residue at position 29 which was determined by a comparison of the elution profile of the acid hydrolysates of the protein and peptides on an amino acid analyzer with three methyl derivatives of lysine and also by field desorption mass spectrometry of a purified peptide. The ferredoxin has only 7 cysteine residues, which probably participate in constructing the Fe-S clusters of this ferredoxin, indicating the presence of a unique chelate structure. Comparison of this ferredoxin with other archaebacterial ferredoxins indicated that the archaebacteria might have multiple origins in an evolutionary tree.

Amino Acid Sequence↗
PubMed1982

Thermoacidophilic archaebacteria contain bacterial-type ferredoxins acting as electron acceptors of 2-oxoacid:ferredoxin oxidoreductases.

Thermoplasma acidophilum and Sulfolobus acidocaldarius contain coenzyme A-acylating 2-oxoacid:ferredoxin oxidoreductases similar to those found in halophilic archaebacteria. A common feature of these enzymes is the formation of a free radical intermediate in the course of the catalytic cycle. The electron-accepting ferredoxins and a similar protein from Desulfurococcus mobilis have been purified and characterized. In contrast to the [2Fe-2S] ferredoxin of Halobacterium halobium, the ferredoxins of thermoacidophilic archaebacteria most likely contain two [4Fe-4S]2 + (2 + .1 +) clusters per molecule. Properties of these proteins are compared with respect to the evolution of archaebacteria.

Amino Acids↗
PubMed1981

Purification and properties of two 2-oxoacid:ferredoxin oxidoreductases from Halobacterium halobium.

Pyruvate:ferredoxin oxidoreductase and 2-oxoglutarate:ferredoxin oxidoreductase were obtained from cell-free extracts of Halobacterium halobium as homogeneous proteins after ammonium sulfate precipitation, salting-out chromatography with ammonium sulfate on unsubstituted agarose, gel filtration and chromatography on hydroxyapatite. The respective molecular weights are 256000 and 248000. Both enzymes consist of two sets of non-identical subunits of Mr 86000 and 42000 in the case of the pyruvate-degrading enzyme and of 88000 and 36000 in the case of the 20 -oxogluatarate-degrading enzyme. Analyses indicate that an intact enzyme molecule contains two [4 Fe-4S]2 + (2 + , 1+) clusters and two molecules of thiamin diphosphate. Flavin nucleotides, lipoic acid and pantetheine are absent. Thus the enzymes are very similar to the 2-oxoacid:ferredoxin oxidoreductases from fermentative and photosynthetic anaerobes described previously, but are clearly different from the 2-oxoacid dehydrogenase multienzyme complexes which commonly occur in anaerobic organisms.

Amino Acids↗
PubMed1981

The catalytic mechanism of 2-oxoacid:ferredoxin oxidoreductases from Halobacterium halobium. One-electron transfer at two distinct steps of the catalytic cycle.

The catalytic cycle of the 2-oxoacid:ferredoxin oxidoreductases from Halobacterium halobium was investigated. The first step is binding of the 2-oxoacid to the enzyme followed by decarboxylation and transfer of one electron to the [4Fe-4S] cluster of the functional unit. The cluster is then reoxidized by ferredoxin or, in the absence of the physiological electron acceptor, by oxygen. In the resulting stable enzyme-intermediate radical the decarboxylation product of the 2-oxoacid remains tightly bound until reaction with coenzyme A caused formation of acyl-CoA and concomitant transfer of the second electron to the cluster, which again is reoxidized by ferredoxin or oxygen. After purification, part of the enzyme molecules still contain the intermediate radical. Enzyme preparations either free of radical or containing enhanced amounts are obtained by treatment with coenzyme A or 2-oxoacid, respectively. Whenever the radical is present in an enzyme molecule the respective binding site for the 2-oxoacid is blocked.

Binding Sites↗
PubMed1978

Complete amino acid sequence of Halobacterium halobium ferredoxin containing an Nepsilon-acetyllysine residue.

1. The complete amino acid sequence of the 2Fe-2S ferredoxin from Halobacterium halobium was determined to be: (formula see text):2. The apoferredoxin chain consists of 128 amino acid residues and has a molecular weight of 14,330. 3. There are only four cysteines in this ferredoxin molecule; they should be involved in the binding of the two iron atoms at the active center. Ther relative positions of these cysteines are similar to those of the cysteines in chloroplast ferredoxins. 4. There is a high degree of homology between H. halobium ferredoxin and chloroplast ferredoxins, though the latter molecules contain only about 98 amino acid residues. 5. H. halobium ferredoxin contains a single residue of Nepsilon-acetyllysine.

Amino Acid Sequence↗
PubMed1976

A new plant-type ferredoxin from halobacteria.

A stable, 2Fe-type ferredoxin has been prepared from Halobacterium halobium and purified by chromatography. A similar ferredoxin was also found in three other Halobacteria. The ferredoxin is present in large amounts-about 1 percent of the total soluble protein. From amino acid composition a molecular weight of 14800 +/- 200 was calculated. The ferredoxin was found to contain two atoms each of iron and sulphide. The midpoint redox potential of the protein is about -345 mV. The electron paramagnetic resonance spectrum of the reduced form shows much similarity to plant and algal ferredoxins with gx = 1.90, gy = 1.97 and gz = 2.07. The same similarity is observed in the optical absorption, optical rotatory dispersion and circular dichroism spectra. However it does not seem to mediate electron transport in the NADP-photoreduction system of chloroplasts. Extracts of the bacterial cells catalyze the reduction of the ferredoxin by NADH.

Amino Acids↗