Characterization and identification of dityrosine cross-linked peptides using tandem mass spectrometry

The use of mass spectrometry coupled with chemical cross-linking of proteins has become a powerful tool for proteins structure and interactions studies. Unlike structural analysis of proteins using chemical reagents specific for lysine or cysteine residues, identification of gas-phase fragmentation patterns of endogenous dityrosine cross-linked peptides have not been investigated. Dityrosine cross-linking in proteins and peptides are clinical markers of oxidative stress, aging, and neurodegenerative diseases including Alzheimer’s disease and Parkinson’s disease. In this study, we investigated and characterized the fragmentation pattern of a synthetically prepared dityrosine cross-linked dimer of Aβ(1–16) using ESI tandem mass spectrometry. We then detailed the fragmentation pattern of dityrosine cross-linked Aβ(1–16), using collision induced dissociation (CID), higher-energy collision induced dissociation (HCD), electron transfer dissociation (ETD), and electron capture dissociation (ECD). Application of these generic fragmentation rules of dityrosine cross-linked peptides allowed for the identification of dityrosine cross-links in peptides of Aβ and α-synuclein generated in vitro by enzymatic peroxidation. We report, for the first time, the dityrosine cross-linked residues in human hemoglobin and α-synuclein under oxidative conditions. Together these tools open up the potential for automated analysis of this naturally occurring post-translation modification in neurodegenerative diseases as well as other pathological conditions

Reactions of nitroplatinum complexes. 1. 15N and 195Pt NMR spectra of platinum(II) nitrite complexes

15N and 195Pt NMR spectra have been used to characterize the products of reaction of Pt(15NO2)42- with sulfamic acid, Pt(15N-O2)3(H2O)- and cis-Pt(15NO2)2(H2O)2, and the hydroxo complexes Pt(15NO2)3(OH)2- and cis-Pt(NO2)2(OH)2 2- derived from them by deprotonation. At intermediate pH values, the dinitro complexes rapidly form the hydroxo-bridged compounds [{Pt-(15NO2)2(μ-OH)}n] 1- (n = 2, 3). The acid dissociation constant for Pt(15NO2)3(H2O)- (pKa 5.32) was determined from the variation with pH of δN for nitro ligands cis to water/hydroxide. 15N and 195Pt NMR parameters were obtained for the series Pt(15NO2)3Zm-. The changes in these parameters as Z was changed correlated with those in the series Pt(15NH3)3Zn+. δN and J(Pt-N) values are much more sensitive to change in the ligand Z for the nitro ligand trans to Z than for that cis to Z

Aspects of the solution chemistry of trans-diammineplatinum(II) complexes

A convenient method for small-scale preparations of trans-[PtCl2(NH3)2] (e.g., for preparing 15N-labeled compounds) is to heat [Pt(NH3)4]Cl2 at 190-195°C, under vacuum. 15N and 195Pt NMR spectra have been used to characterize in solution trans-diammineplatinum(II) complexes with aqua, chloro, nitrato, sulfato, acetato, and phosphato ligands. A solution of trans-[Pt(OH)(H2O)(NH3)2]+ allowed to stand gives a precipitate [{trans-Pt(μ-OH)(NH3)2}n] (NO3)n. 15N NMR spectra have been used to determine acid dissociation constants for trans-[Pt(H2O)2(15NH3) 2]2+ (pKa1 4.35, pKa2 7.40) and for trans-[PtCl(H2O)(15NH3)2] + (pKa1 5.63)

Ring-Opened Adducts of the Anticancer Drug Carboplatin with Sulfur Amino Acids

Inorganic Chemistry3541065-1072INOC

L-Methionine increases the rate of reaction of 5′-guanosine monophosphate with the anticancer drug cisplatin: Mixed-ligand adducts and reversible methionine binding

10.1039/DT9950003721Journal of the Chemical Society, Dalton Transactions223721-372

Amine oxidase activity of β-amyloid precursor protein modulates systemic and local catecholamine levels

The catecholamines dopamine (DA), norepinephrine (NE) and epinephrine (E) are neurotransmitters and hormones that mediate stress responses in tissues and plasma. The expression of β-amyloid precursor protein (APP) is responsive to stress and is high in tissues rich in catecholamines. We recently reported that APP is a ferroxidase, subsuming, in neurons and other cells, the iron-export activity that ceruloplasmin mediates in glia. Here we report that, like ceruloplasmin, APP also oxidizes synthetic amines and catecholamines catalytically (Km NE=0.27 mm), through a site encompassing its ferroxidase motif and selectively inhibited by zinc. Accordingly, APP knockout mice have significantly higher levels of DA, NE and E in brain, plasma and select tissues. Consistent with this, these animals have increased resting heart rate and systolic blood pressure as well as suppressed prolactin and lymphocyte levels. These findings support a role for APP in extracellular catecholaminergic clearance