摘要:

The major routes for making aminoacids and their isotopomers described in the literature are briefly compiled, especially considering about fourty research papers from the last five years. This report concentrates on the introduction of2H,13C,15N,17O and18O into different defined positions of L-α-aminoacids. A scheme of four reaction categories with flowcharts is presented (homologation reactions with labelled cyanide and acetate; α-homologation of labeled glycine; β-homologation and/or amination of labelled alanine equivalents and α-enoic acids, including side chain modifications; and reductive amination and transamination of labelled α-ketoacids). The labelling studies done here include the 1-13C substitution of α-ketoacids by the trimethylsilyl cyanide method, the glycine isotopomer homologation by the azlactone and hydantoin methods, the enzymatic aryl and/or ammonia addition to pyruvate and α-enoic acids, and the enzymatic reductive amination of α-ketoacids under enzymatic or enzymo—electrochemical NAD+recycling.

ISSN:1025-6016    

DOI:10.1080/10256019508234017

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The incidence of Crassulacean acid metabolism (CAM) in plants collected at various habitats in Madagascar was investigated by survey of carbon and hydrogen isotope ratios ((δ13C and δD values). In about 50% of the epiphytic orchids from evergreen higher and lower montane forests the δ13C values were indicative for CAM. The remainder of the species are presumably C3plants. In all samples of malagasy epiphytic leafless orchids comprising 9 species, the δ13C values suggest extreme CAM with CO2uptake proceeding entirely during the night. All terrestrial orchids collected in the lower montane forests obviously acquire external carbon by C3-photosynthesis, whereasLissochilus decaryi, a terrestrial orchid from the semi-arid south of Madagascar and various other species of this genus are CAM plants. This is the first report of CAM occurrence in sympodial terrestrial orchids.

ISSN:1025-6016    

DOI:10.1080/10256019508234018

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Since the end of the 80s elemental analyzer-isotope ratio mass spectrometer connections have been used for the fast, automatic and highly precise determination of carbon and nitrogen content as well as their isotopic composition in one run. But for artificially enriched stable isotopes as tracer in biological processes and since these processes have a high biological variability anyway (e.g. soil processes) the use of these highly precise but also sophisticated and expensive instruments is not required. In this case the use of a quadrupole mass spectrometer connected with an elemental analyzer can offer a low cost alternative. As shown, such coupling is suitable for automatic simultaneous routine analysis of total nitrogen and carbon and their isotopic enrichment (15N,13C) in plant material and soils. The relative standard deviation for15N and13C determination is ⩽2% To meet this precision a careful sample homogenization by grinding is very important. The duration of one measurement is 6–8 min. depending on whether nitrogen alone or both nitrogen and carbon are determined. This enables a high sample throughput.

ISSN:1025-6016    

DOI:10.1080/10256019508234019

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The relation between the ratio of the natural13C and12C isotopes of carbon in silages of a C3species (winter-barley) and a C4species (maize) was examined as a potential marker in rate of passage studies in ruminants concurrently with the external marker titanium(IV)-oxide (TiO2). Diets were formulated to contain 140 g crude protein kg−1dry matter. Two ruminally cannulated steers and two wethers were fed on a diet based on whole-plant winter-barley silage (BS) once daily at 07.00 h. The animals received one single meal of whole-plant maize silage (MS), concurrently with a single dose of TiO2. Animals were then switched back to BS for the remainder of the experiment. Faeces were collected over 5 days post MS feeding. Ruminal pH in steers appeared to be unaffected by switches from C3to C4silage feeding, and vice-versa. In steers, faecal samples peaked in TiO2value approximately 22 to 28 h after dosing, and then declined. Carbon isotope values peaked approximately 31 to 35 h after steers received the C4silage, and then declined. The time of this peak corresponded closely to that from a study which used intrinsically labelled13C forage. Carbon isotope values from faecal samples of wethers showed no clear peak and decline. However, measurement of carbon isotope ratios in neutral detergent fibre of silage and faeces instead of whole material greatly improved curve shaping. Provided that C3and C4forages of similar chemical composition and digestibility are used in order to minimize perturbation of rumen fermentation and subsequent passage processes, naturally occurring differences in stable carbon isotope ratios may be used as passage markers in ruminants. This restriction will limit the potential use of estimating passage rates from naturally occurring differences in carbon isotope ratios to only a few specific cases.

ISSN:1025-6016    

DOI:10.1080/10256019508234020

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Reviewed is the transition period in the history of physics between 1895 and 1905, a decade which began 100 years ago and which is characterized by high scientific activity and creativity with significant results for the further development of natural science. A great number of outstanding scientists, especially physicists, worked in this period. Their important discoveries manifest the beginning of the history of isotopic research.

ISSN:1025-6016    

DOI:10.1080/10256019508234021

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:1025-6016    

DOI:10.1080/10256019508234016

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor