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Muscle Research Unit, Department of Zoology, University of Hull, England

ABSTRACT

The proteins and adenosine triphosphatase activity of the contractile apparatus of Uromastix microlepis were studied and compared with those of a typical homoiotherm (rabbit). Uromastix microlepis is a diurnal lizard which inhabits the desert of the Arabian Peninsula and which experiences temperatures up to 50°C. At temperatures of 37°C, and less, the myofibrils of the lizard were less active than those of the rabbit. However, they were much more thermostable. Therefore at temperatures above 37°C the lizard myofibrils had a higher activity than the rabbit myofibrils. Energies of activation, calculated for a range of temperatures, indicated that the contractile apparatus of Uromastix is designed to work at relatively high physiological temperatures. Polyacrylamide gel electrophoresis suggested a possible difference in the troponin complex of the two species. The implications of enzyme systems designed to work at different temperatures are discussed.