. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 158 A. SZENT-GYORGYI actually the case : if strips of the psoas are extracted at equilibrium length with 50 per cent glycerol, they are found to be entirely inelastic. At 0°, in Ringer, they cannot be stretched at all without breaking, and even at 13° C. extensibility does not exceed two per cent. If, however, ATP is added to the Ringer, the muscle again becomes extensible. Using fibre bundles of mm. diameter, the muscle could readily be stretched at ° C., on an average to 145 per cent of its rest
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. 158 A. SZENT-GYORGYI actually the case : if strips of the psoas are extracted at equilibrium length with 50 per cent glycerol, they are found to be entirely inelastic. At 0°, in Ringer, they cannot be stretched at all without breaking, and even at 13° C. extensibility does not exceed two per cent. If, however, ATP is added to the Ringer, the muscle again becomes extensible. Using fibre bundles of mm. diameter, the muscle could readily be stretched at ° C., on an average to 145 per cent of its rest 10 20 30 40 TEMP C° 50 FIGURE 14. Extensibility of extracted psoas fibres at varied temperature. 100 per cent of rest length (abscissa) means that the fibres are not extensible. The extensibility of the extracted muscle, in absence of ATP, is a function of temperature (Fig. 14). At 0° the muscle is practically not extensible; extensi- bility rises slowly with increasing temperature, rising rapidly at body temperature. The extensibility at higher temeperatures, up to 53°, is not due to denaturation, as shown by the relatively big force needed for extension. Denaturation rapidly sets in at a somewhat higher temperature, 54—55°, where the muscle soon becomes plastic, offering practically no resistance to stretching. This shows that, in absence of ATP, the actomyosin particles in muscle are surrounded by unbalanced forces which link neighboring particles together and make it impossible for them to move relative to one another, turning the system into a rigid, inelastic gel. They are counteracted by heat-agitation. The extensibility of muscle at low temperatures in presence of ATP shows that the elasticity of muscle actually depends on its ATP, which must be present in the resting state linked to the actomyosin. The interdependence of ATP and elasticity also shows that in the psoas the elastic properties observed were predominantly 8 These results are in agreement with prev
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
