PSYCHROPHILIC ENZYMES - MOLECULAR-BASIS OF COLD ADAPTATION

Psychrophilic organisms have successfully colonized polar and alpine r egions and are able to grow efficiently at sub-zero temperatures. At t he enzymatic level, such organisms have to cope with the reduction of chemical reaction rates induced by low temperatures in order to mainta in adequate metabolic fluxes. Thermal compensation in cold-adapted enz ymes is reached through improved turnover number and catalytic efficie ncy. This optimization of the catalytic parameters can originate from a highly flexible structure which provides enhanced abilities to under go conformational changes during catalysis. Thermal instability of col d-adapted enzymes is therefore regarded as a consequence of their conf ormational flexibility. A survey of the psychrophilic enzymes studied so far reveals only minor alterations of the primary structure when co mpared to mesophilic or thermophilic homologues. However, all known st ructural factors and weak interactions involved in protein stability a re either reduced in number or modified in order to increase their fle xibility.