THE EFFECT OF SOFT X-RADIATION ON MYOFIBRILS

Myofibrils, the contractile organelles from striated muscles, have bee n examined in the X-ray microscope to determine the effect of radiatio n on their function and structure. Using X-rays of energy 350-385 eV i n the water window we find that after an exposure to 7.5 x 10(5) photo ns/mu m(2) (calculated to give an absorbed dose of 20 000 Gy) the myof ibrils will no longer contract. The use of the free radical scavenging agent, DMSO, gives some protection to the fibrils. It has also been f ound that after this much irradiation the fibrils lose up to 20% of th eir mass. Further substantial mass loss occurs on subsequent irradiati on. After 25 times the loss-of-function exposure only 30% of the mass remains. Analysis of a series of images of the same myofibril covering this range of exposures shows that the mass is preferentially lost in some areas of the structure and consequently significant structural c hanges occur.