ISSN:
1432-136X
Keywords:
Cold adaptation
;
Enzyme kinetics
;
Substrate affinity
;
Chitinase
;
Antarctic krill, Euphausia superba
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
,
Medicine
Notes:
Abstract N-acetyl-β-d-glucosaminidase, a chitin-degrading enzyme, is highly active in the integument and digestive tract of euphausiids. The enzyme was used as a model to compare temperature-dependent enzymatic parameters of Antarctic krill, Euphausia superba, with those of a euphausiid species (Meganyctiphanes norvegica) found in both the Scandinavian Kattegat and the Mediterranean. Other species examined were an Antarctic isopod, Serolis polita, and a tropical crab, Ocypode ryderi. Enzyme isoforms of NAGase were isolated chromatographically. Temperature optimum (between 30 and 53 °C) and activation-energy (47–59 kJ·mol-1) of isoenzymes were generally unrelated to genotypic cold adaptation. Although pH profiles were temperature-dependent, there was no apparent temperature-related control of activities by pH in the experienced physiological range. In contrast, apparent Michaelis constants showed minima at ambient water temperatures (total range: 0.1–0.6 mol·l-1). Potentially, enzyme variants play a role in acclimatisation regulated by Michaelis constants. Apparently, the rate-limiting effects of polar temperatures are partly compensated in the Antarctic crustaceans by construction of enzymes with substrate affinities similar to those of species from warmer climates. The significance of apparent Michaelis constants in evaluating mechanisms of metabolic cold compensation is discussed. Necessary additional experimental approaches are highlighted.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00309662
Permalink
