ABSTRACT
Stable isotopes have gained prominence in nutrition and trace element research. Fast atom bombardment mass spectrometry (FAB-MS) measurement of iron isotope ratios has an accuracy of > or equal to 99.7% with the stable isotopes (54)Fe, (56)Fe, and (58)Fe with relative standard deviations (RSDs) of < or equal to 0.9%. The isolation of iron from biological matrices can be accomplished in 4 h with almost total removal of isobaric interferences caused by (39)KOH, (39)K.H2O, (40)CaOH, and/or (40)Ca.H2O. FAB-MS isotope enrichment measurements from this method compare favorably to predicted absorption/enrichment levels.
Subject(s)
Erythrocytes/chemistry , Iron Isotopes , Iron/blood , Spectrometry, Mass, Fast Atom Bombardment/methods , Humans , Iron/administration & dosage , Iron/isolation & purificationABSTRACT
A series of ring-substituted 3-phenylpropenes has been examined as mechanism-based inhibitors for the copper protein dopamine beta-hydroxylase. p-HO-, p-CH3O-, m-HO-, m-CH3O-, p-Br-, and p-CN-substituted phenylpropenes all inactivate the enzyme under turnover conditions, requiring ascorbate and oxygen. Replacement of the benzylic hydrogens in 3-(p-hydroxyphenyl)propene with deuterium results in a kinetic isotope effect of 2.0 on kinact/KO2 but in no effect on the partition ratio, Vmax/kinact, consistent with a stepwise mechanism for hydrogen abstraction and oxygen insertion. The partition ratio is unchanged in the pH range from 4.5 to 7.1. Determination of the kinetics of inactivation and the partition ratios for each of these ring-substituted phenylpropenes has allowed determination of the respective V/KO2 values. A linear free energy plot of these values as a function of sigma+ gives a rho value of -1.2, while the partition ratios show only a slight decrease upon going electron-withdrawing groups. The results are consistent with a mechanism for dopamine beta-hydroxylase in which a hydrogen atom is abstracted to form a benzylic radical, which then partitions between hydroxylation and enzyme inactivation.
