Meeting Abstract
We explore the basic principles of pressure tolerance in enzymes of deep-sea fishes using lactate dehydrogenases (LDH) as a case study. We compared enzyme activities under a full range of pressures from two hadal snailfishes (Notoliparis kermadecensis and Pseudoliparis swirei) with a shallow-adapted snailfish, Liparis florae, and an abyssal grenadier, Coryphaenoides armatus. We then quantified the LDH content in muscle homogenates to compare the enzymes’ catalytic efficiency using mass-spectrometric determination of the LDH-specific conserved peptide LNLVQR. While studying the effect of pressure on LDH activity, we discovered an unexpected aspect of adaptation. Existing theory suggests that piezophilic adaptation necessitates a decrease in volume changes in protein transitions under high pressure. However, we observed a substantial increase in specific volume change of inactivation in deep-living species. With this change, the enzyme activities from abyssal and hadal species do not substantially decrease up to 100–200 MPa, well beyond full-ocean depth pressures. In contrast, the activity of the enzyme from the tidepool snailfish, L. florae, decreases nearly linearly from 0.1 to 250 MPa. The increased stability of LDH comes at the expense of decreased catalytic efficiency, which is compensated by increased enzyme contents in high-pressure adapted species. This newly-discovered strategy of pressure adaptation is apparently used when substantial changes in functional enzyme-solvent interactions cannot be eliminated.
