First evidence for an LDL‐ and HDL‐associated nitratase activity that denitrates albumin‐bound nitrotyrosine—Physiological consequences

Abstract

SummaryIn the systemic circulation, LDL occurs in the form of a weakly nitrated LDL-albumin complex (LAC). The question here is whether LAC (or HDL) is able to denitrate the albumin-bound 3-NO 2 -tyrosine (3NT). Nitrated albumin was incubated in the presence of lipoprotein fraction (LPF) to be tested, with or without Ca 21 . After precipitation and centrifugation, supernatants (SNs) and protein pellets (PP) were collected. HCl proteolysis was carried out with deuterated 3NT as an internal standard, and amino acids were derivatized for GC-MS analysis, whereas SNs were used for NO 2 2 /NO 3 2 -fluorimetric assays. A loss of 3NT, higher with albumin-low LDL than with albumin-rich LDL or HDL, was found in PP only in the presence of Ca 21 . c-Tocopherol loading of LPF inhibited 3NT loss. 3NT loss was found for the first time to be stoichiometrically equivalent to NO 3 2 , proving that the 3NT loss must be ascribed to a 3NT-denitrating nitratase activity. 3NT loss and NO 3 2 production that clearly cannot be attributed to PON-1 were impaired by D-penicillamine and phenylacetate, inhibitor, and substrate of PON-1, respectively, leading to speculate on the active site. Finally, nitratase activity and albumin contribute to beneficially convert peroxynitrite (ONOO 2 ) into nonbioactive NO 3 2 . But, in inflammatory conditions, xanthine oxidoreductase is expressed leading to detrimentally reduce O 2 and NO 3 2 into O 2 2 and NO that may interact, reconstituting the ONOO 2 pool. The real consequence of nitratase activity and the physiological significance of nitration/denitration processes remain to be explored. IUBMBIUBMB Life, 60(1): [73][74][75][76][77][78] 2008

Human serum albumin: From bench to bedside

“…However, under inflammatory conditions, xanthine oxidoreductase is expressed leading to detrimentally reduce O 2 and NO 3 -into O 2 ÅÀ and Å NO that in turn may interact, reconstituting the ONOO -pool. As a whole, LDL and HDL are able to denitrate the HSA Tyr-3-NO 2 residues (Khan et al, 1997;Léger et al, 2008).…”

“…Remarkably, 82% of NO in blood ($7 lM) is transported as a S-nitrosothiol bound at the HSA residue Cys34 (Peters, 1996). Additionally, HSA could bind NO at Trp and Tyr residue(s) (Khan et al, 1997;Yamakura and Ikeda, 2006;Léger et al, 2008).…”

Ellagic acid and its methyl‐derivatives inhibit a newly found nitratase activity

“…We have recently established that free albumin (i.e. albumin which is not associated with LDL) once nitrated by PN to form the 3‐NO 2 ‐Tyr residues can be denitrated by a specific protein structure belonging to lipoprotein edifices [LDL and high density lipoprotein (HDL)] [6]. It was observed that the highest nitrase activity is associated to LDL.…”

Early Transient Hypoglycemia Is Associated with Increased Albumin Nitration in the Preterm Infant

“…This is further confirmed by the fact that at D4, PNA levels are similar in normoglycemic and ETH infants. Whether nitroalbumin is denitrated or cleared through increased transendothelial transport [42] remains to be determined, although Leger et al [43] recently reported that nitroalbumin can be denitrated by plasma lipoproteins. We and others have reported earlier that cytosolic [44,45] and mitochondrial [46] proteins are denitrated in cellulo within minutes.…”