Proteome analysis of pyloric ceca: a methodology for fish feed development?

Changing the protein source of fish feed from fish meal to alternative sources of protein will affect traits such as fish growth, quality, and feed utilization. The present investigation was initiated to introduce a two-dimensional gel electrophoresis based proteomic workflow as a tool to investigate feed effects on fish by analyzing protein changes in the fish gut. The workflow was used to study the effect of substituting fish meal in fish feed by alternative sources of protein. Rainbow trout divided into five groups were fed for 72 days with feeds varying in protein composition. By two-dimensional gel electrophoresis proteins extracted from the pyloric ceca were separated, making it possible to measure the abundance of more than 440 protein spots. The expression of 41 protein spots was found to change due to differences in feed composition. By mass spectrometry 31 of these proteins were identified, including proteins involved in digestion (trypsinogen, carboxylic ester hydrolase, and aminopeptidase). The many expression changes indicated that the trout, when adapting to differences in feed formulation, alter the protein composition of the gut.

Identification of carbonylated protein in frozen rainbow trout (Oncorhynchus mykiss) fillets and development of protein oxidation during frozen storage.

Frozen storage of fish is known to enhance lipid oxidation, resulting in the development of an unpleasant rancid taste and odor. Frozen storage of fish is also known to reduce protein solubility, and proteins are expected to be oxidatively modified; however, these oxidative mechanisms are poorly understood. Generally, protein oxidation leads to a wide range of modifications; the most studied being the formation of carbonyl groups. The present work shows, by UV spectrophometric determination of protein carbonyl groups in rainbow trout muscle, that storage at -20 degrees C resulted in a 2-fold increase in protein carbonylation compared to storage at -30 or -80 degrees C. Furthermore, low-salt-soluble proteins in fish that were either fresh or stored for 3 years at -80 degrees C were found to have similar extents of carbonylation. Proteome analysis and two-dimensional immunoblotting of rainbow trout low-salt- and high-salt-soluble proteins gave a detailed description of the protein carbonylation pattern. Several carbonylated proteins were identified by LC-MS/MS, such as nucleoside diphosphate kinase, adenylate kinase, pyruvate kinase, actin, creatine kinase, tropomyosin, myosin light chains 1 and 2, and myosin heavy chain. Furthermore, the results showed a reduced solubility of nucleoside diphosphate kinase in fish stored at -20 degrees C for 2 years compared to fish stored at -80 degrees C. It was observed that low-abundant proteins could be relatively more carbonylated than high-abundant proteins, thereby indicating that some proteins are more susceptible to oxidation than others, due to either their cellular localization, amino acid sequence, or biochemical function.

Changes in cod muscle proteins during frozen storage revealed by proteome analysis and multivariate data analysis.

Multivariate data analysis has been combined with proteomics to enhance the recovery of information from 2-DE of cod muscle proteins during different storage conditions. Proteins were extracted according to 11 different storage conditions and samples were resolved by 2-DE. Data generated by 2-DE was subjected to principal component analysis (PCA) and discriminant partial least squares regression (DPLSR). Applying PCA to 2-DE data revealed the samples to form groups according to frozen storage time, whereas differences due to different storage temperatures or chilled storage in modified atmosphere packing did not lead to distinct changes in protein pattern. Applying DPLSR to the 2-DE data enabled the selection of protein spots critical for differentiation between 3 and 6 months frozen storage with 12 months frozen storage. Some of these protein spots have been identified by MS/MS, revealing myosin light chain 1, 2 and 3, triose-phosphate isomerase, glyceraldehyde-3-phosphate dehydrogenase, aldolase A and two alpha-actin fragments, and a nuclease diphosphate kinase B fragment to change in concentration, during frozen storage. Application of proteomics, multivariate data analysis and MS/MS to analyse protein changes in cod muscle proteins during storage has revealed new knowledge on the issue and enables a better understanding of biochemical processes occurring.

Comparison of methods used for pre-concentrating small volumes of organic volatile solutions.

Eight pre-concentration techniques were compared for their capacity to retain volatile and semi-volatile solutes during evaporation of solvent (dichloromethane). The 2-ml test-samples containing 0.2 ppm or 2 ppm (v/v) of volatile and semi-volatile solutes were concentrated to a final volume of 1 ml, 200 microl and 50 microl, respectively. When pre-concentrating to 50 microl, the highest recoveries for both the diluted (0.2 ppm) and concentrated (2 ppm) solutions were found by passive evaporation in a test tube at 22 degrees C. The pre-concentration time from 2 ml to 50 microl by this method was 19-20 h. Heating the test tube to 47 degrees C yielded lower recoveries in dilute samples, but the recoveries of concentrated samples were only slightly lower than the recoveries obtained by passive evaporation. The evaporation time was decreased to 1-2 h. The recoveries and the reproducibility of these methods were superior to the other pre-concentration methods tested. Loss of solute was apparently mainly caused by the fast vapour streams created when speeding up the process of evaporation by heating or by introducing a gas stream into the tube. This increased co-evaporation and thereby solute loss. The capacity of the methods to trap the escaping vapours and create a reflux determined the capacity of the methods to recover the solutes. The experiments demonstrated that more solute is lost during the pre-concentration of dilute samples compared to more concentrated solutions.