Quantification of calpastatin using an optical surface plasmon resonance biosensor.

An immunological biosensor for calpastatin was developed on a surface plasmon resonance based system (Biacore Q). The performance of the biosensor assay was evaluated using ovine and bovine muscle and heart extracts with known calpastatin activity. In addition, the relationship between immunologically detectable calpastatin at 1 day postmortem and shear force at 14 days postmortem was investigated for bovine longissimus dorsi. Calpastatin biosensor results for several experiments were linearly related to calpastatin activity measurements with correlation coefficients ranging from 0.51 to 0.99. The intra- and inter-assay CVs were <6% (n=12). During postmortem storage, the amount of immunologically detectable calpastatin decreased faster than the inhibitory activity in the enzymatic assay. Probably, the epitope recognized by the antibody is degraded faster than the inhibitory sites of calpastatin during postmortem storage. Calpastatin content at 1 day postmortem was correlated to shear force at 14 days postmortem (r=0.75). It is anticipated that developments in the near future will allow for at-line calpastatin determinations in beef plants. At present, the calpastatin biosensor assay appears suitable for research purposes where large numbers of samples need to be processed for breed evaluation or selection programs because this assay requires less labor than other methods.