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I Zimmer

Publications and source records attributed to I Zimmer.

10 recordsLinked to original sources
PubMed2005

Biochemical properties of isoprene synthase in poplar (Populus x canescens).

Isoprene synthase (ISPS) catalyzes the elimination of pyrophosphate from dimethylallyl diphosphate (DMADP) forming isoprene, a volatile hydrocarbon emitted from many plant species to the atmosphere. In the present work, immunological techniques were applied to study and localize ISPS in poplar leaves (Populus x canescens). Immunogold labeling using polyclonal antibodies generated against His-tagged recombinant ISPS protein detected ca. 44% of ISPS in the stroma of the chloroplasts and ca. 56% of gold particles attached to the stromal-facing side of the thylakoid membranes. ISPS isolated from leaves exhibited the same biochemical properties as the recombinant ISPS without the plastid-targeting peptide heterologous expressed in E. coli, whereas an additional C- or N-terminal His-tag changed the biochemical features of the recombinant enzyme with regard to temperature, pH, and substrate dependence. In comparison to the closely related class of monoterpene synthases from angiosperms and ISPS of oaks, the most striking feature of the poplar ISPS is a cooperative substrate dependence which is characteristic to enzymes with positive substrate activation. The detection of four immunoreactive bands in poplar leaf extracts with isoelectric points from 5.0 to 5.5 and a native molecular weight of ca. 51 kDa give reason for future studies on post-translational modifications of ISPS.

Alkyl and Aryl Transferases↗
PubMed2000

Monoterpene synthase activities in leaves of Picea abies (L.) Karst. and Quercus ilex L.

In addition to direct ecological functions in the interaction of plants with the environment, the emission of monoterpenes, especially from the foliage of evergreen trees, is of great importance for the production of ozone and photochemical oxidants in the troposphere. In the present work, we established a reproducible non-radioactive standard enzyme assay and characterized monoterpene synthase activities in needles of Norway spruce (Picea abies (L.) Karst.) and in leaves of holm oak (Quercus ilex L.). In Norway spruce, the dominant monoterpenes formed were alpha-pinene, camphene, and to a lesser extent beta-pinene and limonene. In holm oak, alpha-pinene, sabinene, and beta-pinene were the main products, while limonene was a minor component. Under optimum conditions, in both Norway spruce and holm oak, monoterpene formation remained constant up to 180 min and 90 min, respectively, and varied with the buffer and Mg2+ and Mn2+ concentrations used. Optimum temperature for monoterpene synthase activity was 40 degrees C in both species; optimal pH ranged between 6.5 and 7.5 in both species. Apparent Michaelis-constants for the substrate GDP were ca. 17.9 +/- 5.1 microM for Norway spruce and ca. 69.4 +/- 22.1 microM for holm oak. Molecular weight determination by FPLC indicated that the monoterpene synthases in Norway spruce and holm oak have native molecular weights of ca. 59 and 50 kDa, respectively.

Cations, Divalent↗
PubMed1995

Chondroitin sulfate and chondroitin/keratan sulfate proteoglycans of nervous tissue: developmental changes of neurocan and phosphacan.

We have studied developmental changes in the structure and concentration of the hyaluronic acid-binding proteoglycan, neurocan, and of phosphacan, another major chondroitin sulfate proteoglycan of nervous tissue that represents the extracellular domain of a receptor-type protein tyrosine phosphatase. A new monoclonal antibody (designated 1F6), which recognizes an epitope in the N-terminal portion of neurocan, has been used for the isolation of proteolytic processing fragments that occur together with link protein in a complex with hyaluronic acid. Both link protein and two of the neurocan fragments were identified by amino acid sequencing. The N-terminal fragments of neurocan are also recognized by monoclonal antibodies (5C4, 8A4, and 3B1) to epitopes in the G1 and G2 domains of aggrecan and/or in the hyaluronic acid-binding domain of link protein. The presence in brain of these N-terminal fragments is consistent with the developmentally regulated appearance of the C-terminal half of neurocan, which we described previously. We have also used a slot-blot radioimmunoassay to determine the concentrations of neurocan and phosphacan in developing brain. The levels of both proteoglycans increased rapidly during early brain development, but whereas neurocan reached a peak at approximately postnatal day 4 and then declined to below embryonic levels in adult brain, the concentration of phosphacan remained essentially unchanged after postnatal day 12. Keratan sulfate on phosphacan-KS (a glycoform that contains both chondroitin sulfate and keratan sulfate chains) was not detectable until just before birth, and its peak concentration (at 3 weeks postnatal) was reached approximately 1 week later than that of the phosphacan core protein. Immunocytochemical studies using monoclonal antibodies to keratan sulfate (3H1 and 5D4) together with specific glycosidases (endo-beta-galactosidase, keratanase, and keratanase II) also showed that with the exception of some very localized areas, keratan sulfate is generally not present in the embryonic rat CNS.

Aging↗
PubMed1994

Hydroxymethyl-phytochelatins [(gamma-glutamylcysteine)n-serine] are metal-induced peptides of the Poaceae.

Exposure of several species of the family Poaceae to cadmium results in the formation of metal-induced peptides of the general structure (gamma-Glu-Cys)n-Ser (n=2-4). They are assumed to be formed from hydroxymethyl-glutathione (gamma-Glu-Cys-Ser) and are termed hydroxymethyl-phytochelatins (hm-PCs) in analogy to the homo-phytochelatins [(gamma-Glu-Cys)n-beta-Ala], discovered in legumes, and the phytochelatins [PCs, (gamma-Glu-Cys)n-Gly] found in most other plants and many fungi. The hm-PCs were isolated from the roots of cadmium-exposed rice (Oryza sativa L. cv Strella), and their structure was confirmed by amino acid analysis after total and enzymic hydrolysis and by tandem mass spectrometry. The hm-PCs probably play a significant role in heavy metal detoxication in rice. In addition to this new form of gamma-Glu-Cys (gamma EC) peptide, PCs and gamma EC peptides without C-terminal Ser or Gly are found. All gamma EC peptides are synthesized without delay after incubation of rice plants in 100 microM CdCl2 in the roots as well as in the shoots. Incubation times exceeding 24 h or higher concentrations of cadmium result in a selective enrichment of gamma EC peptides with higher chain length and an increased ratio of PCs to hm-PCs. gamma EC peptide synthesis is accompanied by a decrease of the glutathione content and an increase of the hydroxymethyl-glutathione content in roots and shoots of rice plants.

Amino Acid Sequence↗
PubMed1985

Reduction of ventricular arrhythmias by atenolol.

The effects of atenolol on ventricular arrhythmias were evaluated in 25 men with significant ventricular ectopy. The patients received 2 weeks each of placebo, 50, 100, and 200 mg of oral atenolol. Efficacy was determined by weekly 24-hour Holter monitors. In 20 patients who completed the protocol, the frequency of total ventricular ectopic beats, ectopic couplets, and ventricular tachycardia was significantly decreased after treatment. The complexity of ventricular ectopy was also decreased as measured by the Lown grade and the proportion of hours in which multiform ectopic beats were present. A therapeutic response, defined as the minimum percentage reduction in ventricular arrhythmias to demonstrate an effect due to atenolol rather than spontaneous variation, was achieved in up to 70% of patients for total number of ectopic beats, 75% for ectopic couplets, and 73% for ventricular tachycardia beats. The results show that oral atenolol is an effective agent for the treatment for ventricular arrhythmias.

Adult↗