KINETIC AND STRUCTURAL ADAPTATIONS OF CYTOPLASMIC MALATE-DEHYDROGENASES OF EASTERN PACIFIC ABALONE (GENUS HALIOTIS) FROM DIFFERENT THERMAL HABITATS - BIOCHEMICAL CORRELATES OF BIOGEOGRAPHICAL PATTERNING
E. Dahlhoff et Gn. Somero, KINETIC AND STRUCTURAL ADAPTATIONS OF CYTOPLASMIC MALATE-DEHYDROGENASES OF EASTERN PACIFIC ABALONE (GENUS HALIOTIS) FROM DIFFERENT THERMAL HABITATS - BIOCHEMICAL CORRELATES OF BIOGEOGRAPHICAL PATTERNING, Journal of Experimental Biology, 185, 1993, pp. 137-150
We measured the effects of temperature on cytosolic malate dehydrogena
ses (cMDHs) from the shell muscle of five species of eastern Pacific a
balone, genus Haliotis, found at different latitudes and/or tidal heig
hts. The apparent Michaelis-Menten constant (K(m)) of coenzyme (nicoti
namide adenine dinucleotide, NADH) was conserved within a narrow range
(11-21 mumol l-1) at physiological temperatures for all species. Howe
ver, elevated temperatures perturbed the K(m) of NADH for cMDHs of the
two species living at higher latitudes and/or lower tidal heights [Ha
liotis rufesens (red) and H. kamtschatkana kamtschatkana (pinto)] to a
much greater extent than for cMDHs of congeners from lower latitudes
and/or higher tidal heights [H. fulgens (green), H. corregata (pink) a
nd H. cracherodii (black)]. The apparent Arrhenius activation energies
for the cMDHs of these five species showed a similar interspecific di
vergence. Furthermore, green, pink and black abalone have cMDHs that a
re more resistant to thermal denaturation than are cMDHs of red and pi
nto abalone. Native gel electrophoresis showed that cMDHs of red and p
into abalone had identical mobilities, whereas cMDHs of green, pink an
d black abalone are distinct both from each other and from that of the
two cold-adapted species. These data suggest that cMDHs from the abal
one species living in warm habitats are adapted to function optimally
at higher temperatures than are the cMDHs of the two species living in
cooler habitats. The relationships suggested by these criteria are in
agreement with other studies that used morphological and molecular in
dices to predict abalone phylogeny. These results therefore provide fu
rther evidence that interspecific variation in protein structure and f
unction may be driven by natural selection based on only small (i.e. s
everal degrees Celsius) differences in average body temperature, and t
hat such selection is an important element of the mechanisms of specie
s formation and the maintenance of biogeographic patterning.