LC/MS characterization of undesired products formed during iodoacetamide derivatization of sulfhydryl groups of peptides

Coupling of a vented column with splitless nanoRPLC-ESI-MS for the improved separation and detection of brain natriuretic peptide-32 and its proteolytic peptides

The circulating concentration of a biomarker for congestive heart failure, Brain (B-type) Natriuretic Peptide (BNP-32), is measured using ELISA based assays in order to rapidly diagnose and monitor disease progression. The lack of molecular specificity afforded by these assays has recently come into question as emerging studies indicate there are potentially multiple heterogeneous forms of BNP in circulation with immunoreactive capabilities. In order to better understand the molecular biology of BNP-32 as it relates to congestive heart failure, it would thus be advantageous to use a detection platform such as Fourier transform ion cyclotron resonance mass spectrometry. This high resolving power mass spectrometer can provide unparalleled molecular specificity and can facilitate identification and characterization of the various molecular forms across all disease states. Unfortunately, BNP circulates at low concentrations (as low as 3fmol/mL). Thus, it will require a collaborative effort from a number of orthogonal front-end technologies to overcome the disconnect between the practical detection limits of this instrument platform and the physiological levels of BNP-32 and its alternative molecular forms. Herein, we begin optimization of these front-end techniques by first enhancing the conditions for online nanoLC-ESI-MS separations of BNP-32 and its proteolytic fragments. Through extensive analysis of various chromatographic parameters we determined that Michrom Magic C8 stationary phase used in conjunction with a continuous, vented column configuration provided advanced chromatographic performance for the nano-flow separations involving intact BNP-32 and its associated tryptic peptides. Furthermore, conditions for the tryptic digestion of BNP-32 were also studied. We demonstrate that the use of free cysteine as an alkylation quenching agent and a secondary digestion within the digestion scheme can provide targeted tryptic peptides with increased abundances. Combined, these data will serve to further augment the detection of BNP-32 by LC-MS.

Identifying residues in antigenic determinants by chemical modification

Chemical modification of the side chains of amino acid residues was one of the first methods developed to investigate epitopes in protein antigens. The principle of the method is that alteration of the structure of a key residue of an epitope by a chemical modification will alter reactivity with antibody by affecting either specificity or avidity or both. Chemical modification has the advantage that it can be applied to discontinuous as well as continuous epitopes and may be of value in identifying cryptic epitopes. We consider here the several recent studies that have applied site-specific chemical modification to the identification of epitopes on antigens, including the use of formaldehyde, glutaraldehyde, and acid anhydrides, to produce allergoids where determinants important to reaction with IgE are modified but the ability to elicit an IgG response is retained. It is noteworthy that modification of amino groups with charge reversal appears to be the most useful approach. The approach to the use of site-specific chemical modification as a tool for the study of protein function is discussed, and emphasis is placed on the necessity to (1) validate the specificity of modification and (2) assess potential conformational change that may occur secondary to modification. Finally, a list of chemical reagents used for protein modification is presented, together with properties and references to use.

Automated derivatization and analysis of malondialdehyde using column switching sample preparation HPLC with fluorescence detection

Analyte derivatization is advantageous for the analysis of malondialdehyde (MDA) as a biomarker of oxidative stress in biological samples. Conventionally, however, derivatization is time consuming, error-prone and has limited options for automation. We have addressed these challenges for the solid phase analytical derivatization of MDA from small volume tissue homogenate samples. A manual derivatization method was first developed using Amberlite XAD-2 (12 mg) as the solid phase. Subsequently an automated column switching process was developed that provided simultaneous derivatization and extraction of the MDA-DH hydrazone product on a cartridge packed with XAD-2, followed by quantitative elution of the product to an analytical LC column (Waters NovoPak C18, 3.9 x 150 mm). The LOD was 0.02 microg/mL and recovery was quantitative. The method was linear (r(2) >0.999) with precision < 5% from the LOQ (0.06 microg/mL) to at least 35 microg/mL. The method was successfully applied to the analysis of small volume (30 microL) mouse tissue homogenate samples. Endogenous levels of MDA in the tissues ranged from 20 to 40 nmol/g tissue (ca. 0.1-0.2 microg/mL homogenate). Compared to conventional MDA analyses, the current method has advantages in automation, selectivity, precision and sensitivity for analysis from very small sample volumes.