Bovine muscle 20S proteasome. III: Quantification in tissue crude extracts using ELISA and radial immunodiffusion techniques and practical applications

The 20S proteasome is a large complex (700 kDa) that exhibits endo- and exo-peptidase activities with wide specificity. In postmortem muscles, several sets of evidence suggest a possible significant contribution of proteasome to meat tenderisation. Hence, an accurate and rapid quantification procedure is needed to attest that new function during the ageing of meat. In the present work, we developed an ELISA test enabling the quantification of nM concentrations of the 20S proteasome. We further tested the radial immunodiffusion (RID) technique described as a more simple method that can quantitatively determine the concentration of an antigen in a complex mixture. The ELISA test allowed us to quantify the 20S protesome in tissue homogenates and fluids with a recovery of 100%, a coefficient of variation lower than 5% and a detection limit of 9 ng/ml. Quantification of the 20S proteasome in various bovine tissue by ELISA showed the highest concentration in liver followed by spleen and kidney, with muscles exhibiting the lowest concentrations. In addition, measurement of the proteasome concentration in eight different bovine muscles with various metabolic profiles led to the conclusion that the relationship between muscle metabolic properties and proteasome concentration is rather complex. Nevertheless, heart muscle exhibited the highest proteasome content (331 μg/g wet tissue) whereas the lowest values were found for M. Tensor Fascia Latae (213 μg/g wet tissue), a fast twitch white muscle, M. Supraspinatus (209 μg/g wet tissue), a slow twitch red muscle and M. Pectoralis profondus (203 μg/g wet tissue), an intermediate muscle. As compared to other endogenous peptidases, muscle tissue contains relatively high amounts of proteasome. Hence this complex can be quantified using the RID, which allows quantification of protein in the μg range. Plotting the concentration values determined with both methods for all bovine tissues tested gave a straight line with a correlation coefficient of 0.99.