Purification and biochemical characterisation of a glucose-6-phosphate dehydrogenase from the psychrophilic green alga Koliella antarctica

摘要

Psychrophilic organisms have evolved a number of modifications of cellular structures to survive in the cold environment; among them it is worth noting an increased efficiency of enzymes at lower temperatures. Glucose-6-phosphate dehydrogenase (G6PDH; EC 1. 1. 1. 49) was purified and characterised from the psychrophilic green alga Koliella antarctica (Trebouxiophyceae, Chlorophyta) from the Ross Sea (Antarctica). It was possible to isolate a single G6PDH using biochemical strategies; its maximum activity was measured at 35 °C, and the enzyme showed an E_a of 39. 6 kJ mol~(-1). This protein reacted with antibodies raised against higher plants plastidic isoforms. KaG6PDH showed peculiar kinetic properties, with a K_(iNADPH) value lower than K_(mNADP)~ +. Notably, catalytic activity was inactivated in vitro by DTT and chloroplastic thioredoxin f. These biochemical properties of G6PDH are discussed with respect to higher plant G6PDHs and the adaptation of K. antarctica to polar low-temperature environment.