Biogeochemistry Program , Japan Agency for Marine-Earth Science and Technology , Yokosuka , Kanagawa 237-0061 , Japan.
Published: February 2020
AI Article Synopsis
Article Abstract
Compound-specific isotope analyses of geoporphyrins, which are derivatives of chloropigments possessed by phototrophs, provide essential records of the biogeochemical cycle of past aquatic environments. Here, we evaluated uncertainties in carbon and nitrogen isotopic compositions (δC and δN) associated with high-performance liquid chromatography (HPLC) purification and isotopic measurements of geoporphyrins. Evaluation of total blank carbon and nitrogen for the HPLC and our sensitivity-improved elemental analyzer/isotope ratio mass spectrometer (nano-EA/IRMS) analysis confirmed that blank carbon can be corrected and that blank nitrogen is negligible compared to the mass of geoporphyrins required for the isotopic measurement. While geoporphyrins exhibited substantial in-peak carbon and nitrogen isotopic fractionations, no systematic changes in δC and δN values were observed during reversed- and normal-phase HPLC isolation of Ni- and VO-porphyrin standards, with the changes in δC and δN values being within ±0.6‰ and ±1.2‰ (2σ), respectively. These values are comparable to the instrumental precision of the nano-EA/IRMS system (±1.3‰ for 0.70 μgC and ±1.1‰ for 0.08 μgN, 2σ), confirming that no substantial artifact in the δC and δN values would be expected during the reversed- and normal-phase HPLC purification. The sensitivity and precision of our method enable us to determine δC and δN values of both major and minor geoporphyrins found in ancient sediments, which would provide detailed information on the photosynthetic primary producers and the carbon and nitrogen cycles in the past.
Purpose: To compare VEP and fMRI as a means of detecting the abnormal visual projections in albinism in different stimulation conditions.
Methods: Cortical response to monocular full-field pattern-onset and hemifield pattern-onset and -reversal stimulation of 18 subjects with a known diagnosis of albinism, 17 control subjects, and 6 control subjects with infantile nystagmus syndrome (INS) was determined by VEP and fMRI. An asymmetry index was used to quantify the extent of response lateralization as measured by both VEP and fMRI.
Protein synthesis and turnover in ruminal micro-organisms were assessed by stable-isotope methods in order to follow independently the fate of amino acid (AA)-C and -N in different AA. Rumen fluid taken from sheep receiving a grass hay-concentrate diet were strained and incubated in vitro with starch-cellobiose-xylose in the presence of NH3 and 5 g algal protein hydrolysate (APH)/l, in incubations where the labels were (15)NH3, [(15)N]APH or [(13)C]APH. Total (15)N incorporation was calculated from separate incubations with (15)NH3 and [(15)N]APH, and net N synthesis from the increase in AA in protein-bound material.
