Irradiations of rabbit myofibrils with an ultraviolet microbeam. I. Effects of ultraviolet light on the myofibril components necessary for contraction.
Glycerinated rabbit psoas myofibrils, F-actin, and myofibril ghosts were irradiated with ultraviolet light (UV) to investigate how UV blocks myofibril contraction. Myofibril contraction is most sensitive to 270- and 290-nm wavelength light. We irradiated I and A bands separately with 270- and 290-nm wavelength light using a UV microbeam and constructed dose-response curves for blocking sarcomere contraction. For both wavelengths, irradiations of A bands required less energy per area to block contraction than did irradiations of I bands, suggesting that the primary effects of both 270- and 290-nm wavelength light in stopping myofibril contraction are on myosin. We investigated whether the primary effect of UV in blocking I-band contraction is the depolymerization of actin by comparing the relative sensitivities of I-band contraction, F-actin depolymerization, and thin filament depolymerization to 270- and 290-nm light. We also compared the dose of UV required to depolymerize F-actin in solution with the dose needed to block I-band contraction and the dose required to alter thin filament structure in myofibril ghosts. The results confirm that UV blocks I-band contraction by depolymerizing actin. We discuss how the results might be relevant to the hypothesis that an actomyosin-based system is involved in chromosome movement.
D000199:Actins / Q000378:metabolism / Q000528:radiation effects; D000818:Animals; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000528:radiation effects*; D009132:Muscles / Q000502:physiology / Q000528:radiation effects; D009210:Myofibrils / Q000502:physiology / Q000528:radiation effects* / Q000648:ultrastructure; D009218:Myosins / Q000302:isolation & purification; D011817:Rabbits; D012518:Sarcomeres / Q000502:physiology / Q000528:radiation effects; D014466:Ultraviolet Rays
D000199:Actins; D009218:Myosins