Helle Malerod

Bio: Helle Malerod is an academic researcher from University of Oslo. The author has contributed to research in topics: Hydrophilic interaction chromatography & High-performance liquid chromatography. The author has an hindex of 13, co-authored 15 publications receiving 575 citations. Previous affiliations of Helle Malerod include Oslo University Hospital.

A Critical Review of Trypsin Digestion for LC-MS Based Proteomics

Abstract: Proteomics is defined as the large-scale study of proteins in particular for their structures and functions (Anderson and Anderson 1998), and investigations of proteins have become very important since they are the main components of the physiological metabolic pathways in eukaryotic cells. Proteomics increasingly plays an important role in areas like protein interaction studies, biomarker discovery, cancer prevention, drug treatment and disease screening medical diagnostics (Capelo et al. 2009). Proteomics can be performed either in a comprehensive or “shotgun” mode, where proteins are identified in complex mixtures, or as “targeted proteomics” where “selective reaction monitoring” (SRM) is used to choose in advance the proteins to observe, and then measuring them accurately, by optimizing the sample preparation as well as the LC-MS method in accordance to the specific proteins (Mitchell 2010). Whether “MS-based shotgun proteomics” has accomplished anything at all regarding clinically useful results was recently addressed by Peter Mitchell in a feature article (Mitchell 2010), and he states that the field needs to make a further step or even change direction. Referring to discussions with among others John Yates and Matthias Mann, Mitchell addresses the failure in the search for biomarkers as indicators of disease, the difficulties of protein arrays, the uncertainty of quantification in “shotgun proteomics” (due to among others the efficiency of ionization in the mass spectrometers), database shortcomings, the problems of detecting post translational modifications (PTMs), and finally the huge disappointment in the area of drug discovery. The field points in the direction of targeted proteomics, but targeted proteomics will not be the solution to all our questions and comprehensive proteomics will still be needed. In order to get as much information, with as high quality as possible, from a biological sample, both the sample preparation and the final LC-MS analyses need to be optimized. The most important step in the sample preparation for proteomics is the conversion of proteins to peptides and in most cases trypsin is used as enzyme. Trypsin is a protease that specifically cleaves the proteins creating peptides both in the preferred mass range for MS sequencing and with a basic residue at the carboxyl terminus of the peptide, producing information-rich, easily interpretable peptide fragmentation mass spectra. Some other proteases can be used as well, such as Lys-C, which is active in more harsh conditions with 8 M urea, and give larger fragments than trypsin. Asp-N and Glu-C are also highly sequence-

Recent advances in on-line multidimensional liquid chromatography

Abstract: Multidimensional liquid chromatography (MD LC) has, due to enhanced peak capacity compared to one-dimensional LC, become an important analytical tool for separating components in complex samples, e.g. in proteomics. MD LC can be performed both on-line and off-line. Because of the advantages like possible automation and minimal sample loss, on-line MD LC has appeared to be very attractive also for high throughput analysis. This review includes only on-line coupled MD LC. Different aspects related to the compatibility of separation principles and column dimensions are highlighted and recent applications using on-line mainly two-dimensional (2D) LC have been included.

Electrochemically mediated atom transfer radical polymerization

Abstract: Electrochemical reduction of an exemplary ATRP catalyst, C 11 Br 2 /Me 6 TREN, is shown to be an efficient process to mediate and execute an ATRP. The onset of polymerization occurs only through passage of a cathodic current achieved under a reductive potential to form Cu 1 Br 2 /Me 6 TREN, within the reaction medium. Unprecedented control over the polymerization kinetics can be attained through electrochemical methods by modulating the magnitude of the applied potential allowing polymerization rate enhancement or retardation. Additional polymerization control is gained through electrochemical “dials” allowing polymerization rate enhancements achieved by larger applied potentials and the ability to successfully switch a polymerization “on” and “off between dormant and active states by application of multistep intermittent potentials.

Solid-phase extraction of organic compounds: A critical review (Part I)

Abstract: Solid-phase extraction (SPE) is the most widely used method for the extraction, changing of solvents, cleanup, concentration, and fractionation of organic compounds from a number of samples. This procedure is also very useful for desalting proteins and sugar samples. However, most SPE procedures are still poorly developed, with little consideration to the physics involved in the process and are described as largely empirical, labor-intensive, and time-consuming trial-and-error processes, without much systematization. The objective of this study is to propose a number of contradictions, disagreements, failings, and shortcomings of the SPE procedures found elsewhere. The different arguments introduced in this study attempt to challenge the suitability of this procedure, particularly when it is conducted in the traditional manner (under gravity and at a high flow rate). The first part of this study focuses on describing the state-of-the-art in SPE and its physical fundamentals.