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Biomedical subjects

M H Zenk

Publications and source records attributed to M H Zenk.

At least 19 recordsLinked to original sources
PubMed1992

The jasmonate precursor, 12-oxo-phytodienoic acid, induces phytoalexin synthesis in Petroselinum crispum cell cultures.

The pentacyclic biosynthetic precursor of jasmonic acid, 12-oxo-phytodienoic acid, was found to induce synthesis of the major flavonoid, apiin, in cell suspension cultures of Petroselinum crispum. The accumulation of apiin was preceded by an increase in the relative levels of poly (A)+ RNAs that code for the flavonoid biosynthetic enzymes phenylalanine ammonia lyase, 4-coumarate:CoA ligase and chalcone synthase, Poly (A)+ RNAs reached maximal levels at approximately 4-6 h after the addition of elicitor while flavonoids continued to accumulate in the cultures for at least 6 days. 12-Oxo-phytodienoic acid is the first pentacyclic precursor in the jasmonic acid biosynthetic chain which functions as a signal transducer for phytoalexin induction.

Blotting, Northern↗
PubMed1992

Saccharomyces cerevisiae and Neurospora crassa contain heavy metal sequestering phytochelatin.

In fungi, cellular resistance to heavy metal cytotoxicity is mediated either by binding of metal ions to proteins of the metallothionein type or by chelation to phytochelatin-peptides of the general formula (gamma-Glu-Cys)n-Gly. Hitherto, only one fungus, Candida glabrata has been shown to contain both metal inactivating systems. Here we show by unambiguous FAB-MS analysis that both a metallothionein-free mutant of Saccharomyces cerevisiae as well as a wildtype strain synthesize phytochelatin (PC2) upon exposure to 250 microM Cd2+ ions. The presence of Zn and/or Cu ions in the nutrient broth also induces PC2 synthesis in this organism. By 109Cd exchange and subsequent monobromobimane fluorescence HPLC, it could be shown that the presence of Cd2+ in the growth medium also induces phytochelatin synthesis in Neurospora crassa, which contains metallothioneins.

Cadmium↗
PubMed1991

Reactivation of metal-requiring apoenzymes by phytochelatin-metal complexes.

The enzymatically inactive, metal-requiring apoforms of diamino oxidase and of carbonic anhydrase were reactivated by copper-and zinc-phytochelatin complexes, respectively. The level and the rate of reactivation effected by metal complexes consisting of poly(gamma-glutamylcysteinyl)glycine as well as by the respective free metal ion were compared. An efficient transfer of zinc and copper from phytochelatin-complexes to apoenzymes was observed in vitro.

Amine Oxidase (Copper-Containing)↗
PubMed1991

Phytochelatins.

Explore the source record for details and available documents.

Amino Acid Sequence↗
PubMed1991

Immunologically active polysaccharides of Arnica montana cell cultures.

From the nutrition medium of Arnica montana cell cultures two homogeneous polysaccharides, an acidic arabino-3,6-galactan-protein with mean Mr of 100,000 and a neutral fucogalactoxyloglucan with mean Mr of 22,500 have been isolated by DEAE-Sepharose CL-6B and Sephacryl S-400 column chromatography. Their structures were elucidated mainly by methylation analysis, partial acidic and enzymatic hydrolysis and 13C NMR spectroscopy. The fucogalactoxyloglucan shows a pronounced enhancement of phagocytosis in vivo. The arabino-3,6-galactan-protein displays a strong anticomplementary effect and stimulates macrophages to excrete the tumour necrosis factor (TNF alpha).

Carbohydrate Sequence↗
PubMed1990

Radioimmunoassay for the quantitative determination of galanthamine.

A radioimmunoassay for the quantitation of pmol amounts of the therapeutically important Amaryllidaceae alkaloid, galanthamine, has been developed. The antiserum was raised against a conjugate of galanthamine-2-O-hemisuccinate-bovine serum albumin. The measuring range of the assay extends from 0.5 to 100 ng of galanthamine, and as little as 3.5 pmol may be detected. The antiserum is highly specific for galanthamine, showing practically no cross reactivity with different representatives of the most frequently occurring types of alkaloidal structures in Amaryllidaceae. This assay enables a rapid, sensitive and precise quantitation of galanthamine in unpurified plant extracts. The galanthamine concentration in bulbs of several Leucojum aestivum plants and the distribution of galanthamine in some Amaryllidaceae genera of South African origin have been investigated. Preliminary experiments indicate that the galanthamine-specific radioimmunoassay can be a useful tool in medicinal plant breeding as well as in tissue and cell culture studies.

Animals↗
PubMed1988

The cDNA clone for strictosidine synthase from Rauvolfia serpentina. DNA sequence determination and expression in Escherichia coli.

The cDNA clone for strictosidine synthase, the enzyme which catalyzes the stereospecific condensation of tryptamine with secologanin to form the key intermediate in indole alkaloid biosynthesis, strictosidine, has been identified with a synthetic oligodeoxynucleotide hybridization probe in a lambda gt11 cDNA library of cultured cells of Rauvolfia serpentina. The DNA has been sequenced, revealing an open reading frame of 1032 base pairs encoding 344 amino acids. The sequence of 60 nucleotides in the 5'-flanking region has been determined by primer extension analysis. The encoded protein has been expressed in E. coli DH5 as detected by immunoblotting of protein extracts with antibodies raised against the native enzyme.

Amino Acid Sequence↗
PubMed1988

Purification and properties of (S)-tetrahydroprotoberberine oxidase from suspension-cultured cells of Berberis wilsoniae.

A novel oxidase, catalyzing in the presence of oxygen the removal of four hydrogen atoms from a number of tetrahydroprotoberberines with simultaneous production of 1 mol H2O2 and H2O each, has been discovered and purified to homogeneity from Berberis wilsoniae cell cultures. This enzyme, (S)-tetrahydroprotoberberine oxidase, exhibited strict specificity for the (S)-enantiomer of tetrahydroprotoberberines and 1-benzylisoquinoline alkaloids, a pH optimum at 8.9, a molecular mass of 105 kDa and consisted of two subunits each of 53 kDa and covalently bound flavin. The Km values for (S)-scoulerine and (S)-norreticuline were 25 microM and 150 microM respectively. Concentration of the end-products, either protoberberines or H2O2, greater than 0.5 mM caused severe enzyme inhibition. This catalyst was responsible for the conversion of (S)-tetrahydrocolumbamine to the key intermediate, columbamine, in the metabolic pathway leading to berberine, jatrorrhizine and palmatine.

Berberine Alkaloids↗
PubMed1987

Analysis, cloning, and high-level expression of 2,4-dichlorophenoxyacetate monooxygenase gene tfdA of Alcaligenes eutrophus JMP134.

Plasmid pJP4 of Alcaligenes eutrophus JMP134 contains all genes for the degradation of 2,4-dichlorophenoxyacetic acid (2,4-D). Five of these genes, tfdB, tfdC, tfdD, tfdE, and tfdF, have recently been localized and cloned (R. H. Don, A. J. Weightman, H.-J. Knackmuss, and K. N. Timmis, J. Bacteriol. 161:85-90, 1985). Gene tfdA, which codes for the 2,4-D monooxygenase, has now been found by mutagenesis with transposon Tn5. A 3-kilobase fragment of pJP4 cloned in a broad-host-range vector could complement the 2,4-D-negative phenotype of two mutants which lacked 2,4-D monooxygenase activity. The cloned tfdA gene was also transferred to A. eutrophus JMP222, which is a cured derivative of JMP134. The recombinant strain could utilize phenoxyacetic acid as a sole source of carbon and energy. Pseudomonas sp. strain B13, containing the cloned tfdA, was able to degrade phenoxyacetic acid and 4-chlorophenoxyacetic acid. Gene tfdA was subcloned and analyzed by deletions. Expression of 2,4-D monooxygenase in Escherichia coli containing a 1.4-kilobase subfragment was demonstrated by radioisotopic enzyme assay, and a protein of 32,000-dalton molecular mass was detected by labeling experiments. A 2-kilobase subfragment containing tfdA has been sequenced. Sequence analysis revealed an open reading frame of 861 bases which was identified as the coding region of tfdA by insertion mutagenesis.

Alcaligenes↗
PubMed1979

Purification and properties of strictosidine synthase, the key enzyme in indole alkaloid formation.

A new enzyme, strictosidine synthase, which catalyzes the synthesis of 3-alpha(S)-strictosidine from tryptamine and secologanin was isolated from the soluble protein extract of Catharanthus roseus cell suspension cultures and was purified approximately 50-fold by ammonium sulfate fractionation, column chromatography on DEAE-cellulose. Ultrogel AcA34 and isoelectric focusing. The apparent molecular weight of the enzyme was 34000. The pH optimum was 6.8, apparent Km values for tryptamine and secologanin were 2.3 mM and 3.4 mM respectively for the enzyme to synthesize strictosidine. Strictosidine synthase shows high substrate specificity. No apparent cofactor requirement could be demonstrated. Of several enzyme inhibitors tested, only p-chloromercuribenzoate inhibited the enzyme. The enzyme was relatively stable and could be stored at -20 degrees C for periods of up to 1 year without appreciable loss of catalytic activity. The enzyme was demonstrated to occur in suspension cultures of 15 different species belonging to 9 different genera of the indole-alkaloid-producing subfamily Plumerioideae of the Apocynaceae family. This enzyme is responsible for the synthesis of strictosidine the key intermediate in the formation of the majority of monoterpenoid indole alkaloids occurring in the plant kingdom.

Cells, Cultured↗
PubMed1979

Iodinated digoxin derivatives with improved reactivity and stability, for use in radioimmunoassay.

We report the synthesis and properties of a new digoxin derivative, prepared by reacting cyanogen bromide-activated digoxin with tyramine. The derivative is extremely stable, and its monoiodinated form can be isolated in 85--90% purity by a single thin-layer chromatographic step. [125I]Tyramine-digoxin is immunologically stable for at least four months (immunoreactivities, 90% or greater throughout), with a shelf life of about six months. Nonspecific binding of less than 10% was observed for several batches during this time.

Digoxin↗