Nanosecond pulse fluorometry in polarized light of dansyl-L-cysteine linked to a unique SH group of F-actin; the influence of regulatory proteins and myosin moiety.
The order of magnitude of the correlation time, which characterizes the dansyl cysteine residue linked to F-actin is ten times greater than the correlation time of the G-actin monomer [1]. Still it is much smaller than the correlation times of the F-actin polymer as a whole. The dansyl chromophore reveals that the C terminal end of the actin peptide chain, is mobile. As Ebashi and his co-workers have shown (13), Ca2+ triggers muscular contraction by acting on F-actin through the mediation of the regulatory proteins troponin and tropomyosin. By using spin label technique, Tonomura et al. [14] found that Ca2+ induces a conformational change on the troponin, tropomyosin actin complex. The quasi elastic scattering of laser light measurement of Fujime and Ishiwata [15] showed that troponin-tropomyosin F-actin has a rotational correlation time in the millisecond range which characterizes the flexibility of this complex; Ca2+ induces an increase of this flexibility. The present pulse fluorometry study shows an increase of mobility of the fluorescent probe induced by Ca2+. It seems difficult to correlate the results of the two kinds of measurements as long as we do not know the exact nature of the fluorescent kinetics unit.
D000199:Actins / Q000031:analogs & derivatives; D000818:Animals; D002118:Calcium; D003619:Dansyl Compounds; D015879:Myosin Subfragments; D009904:Optical Rotation; D011487:Protein Conformation; D011817:Rabbits; D013050:Spectrometry, Fluorescence; D014335:Tropomyosin; D014336:Troponin
D000199:Actins; D003619:Dansyl Compounds; D015879:Myosin Subfragments; D014335:Tropomyosin; D014336:Troponin; D002118:Calcium