carbobenzoxycarbonyl-l-phenylalanyl-l-alanine-d-diazomethane and pepstatin

The effects of in situ postrigor injection (24 h postmortem) of exogenous aspartic, serine, and cysteine proteinase effectors into cylindrical beef longissimus samples on tenderness and myofibrillar protein degradation and integrity were studied. Injection of phenylmethanesulphonylfluoride (PMSF) and pepstatin did not influence shear force or protein degradation measured 8 d postmortem, confirming that neither serine nor aspartic proteinases affect tenderization. Injection of leupeptin, an epoxysuccinyl peptide (E-64), or N-acetyl-Leu-Leu-norleucinal (calpain inhibitor I) blocked tenderization completely, as observed by higher (P < .05) shear force values. A causal relationship between increased toughness and prevented action of the cysteine proteinases was suggested by a concomitant reduction of myofibrillar protein degradation, generally reflected in higher (P < .05) remaining troponin-T and titin amounts and lower (P < .05) levels of 30-kDa peptide, as evaluated by semiquantitative SDS-PAGE. Moreover, parallel to these changes, amounts of salt-soluble myofibrillar protein and semiquantitative concentrations of individual salt-soluble proteins (SDS-PAGE) were also reduced (P < .05). Injection of Triton-X-100 and Ca2+ increased (P < .05) tenderness, as well as myofibrillar protein degradation and solubility, and free Ca2+, whereas EDTA induced the opposite results, indicating an important role for calpains in tenderization. Because cathepsin B, D, H, and L inhibitors did not affect texture or proteolysis, our results suggest that calpains are the main proteases involved in beef tenderization.

Topics: Animals; Calcimycin; Calcium; Calpain; Cathepsins; Cattle; Cysteine Proteinase Inhibitors; Diazomethane; Edetic Acid; Electrophoresis, Polyacrylamide Gel; Endopeptidases; Glycoproteins; Leucine; Leupeptins; Male; Meat; Muscle Proteins; Muscles; Octoxynol; Pepstatins; Phenylmethylsulfonyl Fluoride; Postmortem Changes; Solubility

The effect of the lysosomotropic agent NH4Cl and the proteinase inhibitors leupeptin, Z-Phe-Ala-CHN2 (benzyloxycarbonylphenylalanylalanyldiazomethane) and pepstatin on the degradation of intracellular proteins in Swiss 3T3 mouse and normal human fibroblasts in both the exponential and stationary (confluent) growth phases in nutritionally complete conditions was investigated. Inhibitory effects of all four agents on degradation in both growth states were detected. The increase in proteolysis normally occurring as cells approach confluence could be completely blocked by NH4Cl, by Z-Phe-Ala-CHN2, or by pepstatin in the presence of leupeptin. These results suggest that the lysosomal system is responsible for the regulation of proteolysis at confluence and further confirm its role in 'basal' proteolysis in growing cells.

Topics: Ammonium Chloride; Animals; Cells, Cultured; Diazomethane; Fibroblasts; Humans; Leupeptins; Lysosomes; Mice; Pepstatins; Proteins