Nanosecond fluorescence depolarization studies on actin labeled with 1,5‐IAEDANS and dansyl chloride

Fluorescence depolarization studies on the rotational relaxation behavior of G-and F-actin have been performed [l-5] .For G-actin, such studies yield information on the size, shape and aggregation state of the monomer.More interestingly, such studies on F-actin can yield information on the flexibility of the polymer.This property may be significant to the structure and function of the thin fdaments, especially when it pertains to cooperative behavior related to calcium regulation of muscle contraction.While the results of these studies on G-actin are generally in agreement with each other, there are discrepancies in the results reported for F-actin, When labeled with e-ADP, F-actin exhibited no detectable fluorescence depolarization within the time scale of the experiment, and the rotational correlation time was estimated to be >lO ~.rs at 21°C [3].Yet F-actin labeled with either didansyl cystine [4] or pyrene maleimide [5] exhibited measurable depol~ization, yielding correlation times of the order to 500 ns at room temperature.Furthermore, correlation times obtained from other physical studies did not agree with the Abbreviations: 1,5-IAEDANS, N-iodoacetyl-IV'-(5.sulfo-lnaphthyl)-ethylenediamine; AEDANS-G, 1 ,S.IAEDANS.labeled G-actin; AEDANS-F, 1,5-IAEDANS-labeled F-actjn;