The hydrolysis process and the quality of amino acid analysis: ABRF-94AAA collaborative trial

Determination of the experimental extinction coefficient of therapeutic proteins using the Edelhoch method

The objective of this study was to determine how the theoretical values of the extinction coefficient (EC) compares to the experimentally determined extinction coefficient for a large set of biotherapeutic proteins measured by the Edelhoch method. We have performed extensive analysis based on over 176 observations covering 19 different types of molecules from different structural classes covering mAbs, bispecific antibodies, fusion proteins and BiTE molecules. Precision was measured by assessing the repeatability of the measurements for each molecule and determining the relative standard deviation (%RSD). The maximum RSD observed for any given molecule was 1.7% with an average RSD of 0.9%. Deviation from the theoretical extinction coefficient was determined by calculating the experimental bias first, which is the difference between the mean experimental extinction coefficient and the theoretical extinction coefficient. The percent bias (%bias) was then calculated as (bias ÷ theoretical EC) × 100. The maximum %bias observed for any given molecule was 5.3% with an average %bias of 2.6%. Our results indicate that the Edelhoch method is highly reliable with significant improvement in execution efficiency with reduction in cost, time and improvements in safety when compared to the commonly used methods such as amino acid analysis (AAA) technique.

Chromatographic Method for Determination of the Amino Acid Content in Dioscorea bulbifera L. Tubers by RP-HPLC

Background: The present study was carried out for determination of amino acid content in tubers of Dioscorea bulbifera using reverse-phase high-performance liquid chromatography. Methods: The method involved the vapor phase hydrolysis of the sample, automated derivatisation of the amino acids with the aid of AccQ-Fluor reagent kit, separated on a high performance liquid chromatography equipped with photo diode array (HPLC-PDA) at 254 nm having column temperature of 37 ºC. Results: The proportional molar concentration for each amino acid was calculated based on the concentration of standard amino acids and expressed as μg amino acid/mg sample. Methionine, aspartic acid and leucine were major components while as tyrosine was found minor from the plant on dry weight basis. Conclusion: The method is reliable, simple and economical for determining the amino acid content of Dioscorea bulbifera tubers.

Amino acid composition in eyes from zebrafish (Danio rerio) and sardine (Sardina pilchardus) at the larval stage

A comparative study was performed to identify differences in the amino acid composition of the eyes from zebrafish (Danio rerio) and sardine (Sardina pilchardus) larvae and their link to the environmental adaption of the species. Amino acids in the acidic hydrolysates of eyes from 11 zebrafish and 12 sardine were determined with the use of high-performance liquid chromatography involving precolumn derivatization with ortho-phthalaldehyde. Differences in the content of most amino acids were detected between zebrafish and sardine. These amino acids were aspartate, glutamate, serine, glycine, threonine, arginine, methionine, valine, phenylalanine, isoleucine, leucine and lysine. Of particular note, the percentage of methionine in zebrafish eyes was much higher than that in sardine, whereas the opposite was observed for glutamate and glycine. These results indicate that zebrafish and sardine likely have experienced differences in adaptation to environmental changes. We suggest that the amino acid composition of eyes represents a powerful tool to discriminate between species characterized by different lifestyle and inhabiting different environments.

Amino acid analysis

Amino acid analysis (AAA) is one of the best methods to quantify peptides and proteins. Two general approaches to quantitative AAA exist, namely, classical postcolumn derivatization following ion-exchange chromatography and precolumn derivatization followed by reversed-phase HPLC (RP-HPLC). Excellent instrumentation and several specific methodologies are available for both approaches, and both have advantages and disadvantages. This unit focuses on picomole-level AAA of peptides and proteins using the most popular precolumn-derivatization method, namely, phenylthiocarbamyl amino acid analysis (PTC-AAA). It is directed primarily toward those interested in establishing the technology with a modest budget. PTC derivatization and analysis conditions are described, and support and alternate protocols describe additional techniques necessary or useful for most any AAA method--e.g., sample preparation, hydrolysis, instrument calibration, data interpretation, and analysis of difficult or unusual residues such as cysteine, tryptophan, phosphoamino acids, and hydroxyproline.

Hydrolysis and amino acid composition of proteins

Amino acid composition analysis is a classical protein analysis method, which finds a wide application in medical and food science research and is indispensable for protein quantification. It is a complex technique, comprising two steps, hydrolysis of the substrate and chromatographic separation and detection of the residues. A properly performed hydrolysis is a prerequisite of a successful analysis. The most significant developments of the technology in the last decade consist in the (i) reduction of the hydrolysis time by the use of microwave radiation energy; (ii) improvement in the sensitivity of the residue detection, the quantification of the sensitive residues and separation of the enantiomeric forms of the amino acids; (iii) application of amino acid analysis in the large-scale protein identification by database search; and (iv) gradual replacement of the original ion exchange residue separation by reversed-phase high-performance liquid chromatography. Amino acid analysis is currently facing an enormous competition in the determination of the identity of proteins and amino acid homologs by the essentially faster mass spectrometry techniques. The amino acid analysis technology needs further simplification and automation of the hydrolysis, chromatography and detection steps to withstand the pressure exerted by the other technologies.

Effect of the hydrolysis method on the determination of the amino acid composition of proteins

Fast and reproducible separation and determination of amino acids serves the economical and reliable characterization and quantification of peptides and proteins as well as the identification of proteins by amino acid composition analysis on a large-scale. A prerequisite of a successful compositional analysis is a complete hydrolysis of the peptides and proteins and a quantitative recovery of the residues in the hydrolyzate. We investigated the effect of different acid-hydrolysis methods on the compositional analysis of known proteins in solution and after blotting onto polyvinylidene difluoride membranes and worked out the conditions for the processing of large numbers of samples. The reliability of each method was studied by introducing the analysis data into the AACompIdent software and deducing the protein identification scores. All acid-hydrolysis methods delivered reliable analysis data. The most accurate data were provided by conventional, thermal hydrolysis of proteins in solution in the presence of methanesulfonic acid, closely followed by hydrolysis with hydrochloric acid and microwave radiation-dependent hydrolysis with hydrochloric or methanesulfonic acid, respectively. For blotted proteins, conventional hydrolysis delivered more accurate analysis data in comparison with the microwave radiation-induced hydrolysis. The extraction of the residues from the membrane hydrolyzate was a critical step for unambiguous protein identification. Microwave radiation-induced hydrolysis was responsible for a higher degree of racemization of the residues.