Proteolysis at pressure and HPLC peptide mapping of M4-lactate dehydrogenase homologs from marine fishes living at different depths.

1. The effects at 10 degrees C of moderate hydrostatic pressure (136 atm) on trypsinolysis of muscle-type (M4) lactate dehydrogenase homologs (LDH, EC 1.1.1.27, L-lactate:NAD+ oxidoreductase) from shallow- and deep-occurring marine fishes were examined by mapping the partial digests by reverse phase HPLC. 2. Comparison of peptide maps of digests generated at 1 and 136 atm revealed that increased pressure did not expose new cleavage sites in homologs of any of the species; no new peptides were generated. 3. Increased pressure did alter the relative amounts of peptides produced. The net effect of increased pressure was to increase the amount of peptides generated in the shallow-occurring species. For deep-living species pressure did not alter the net amount of peptides produced compared to the 15 min atmospheric pressure samples, although the relative amounts of some of the peptides changed. Incubation at 136 atm for 30 min decreased the net amount of peptides produced. 4. It is suggested that the effects of pressure on trypsinolysis may result from slight conformational changes in the substrate proteins.