'Freezing' of the calcium-regulated structures of gizzard thin filaments by glutaraldehyde

Reconstituted thin filaments (the actin-tropomyosin-leiotonin complex) of chicken gizzard were cross-linked with glutaraldehyde either in the presence or absence of Ca2+. The ability of resultant thin filaments to activate myosin ATPase was 'frozen' in the activated or inactivated state, respectively. This result clearly indicates the existence of actin-linked regulation in smooth muscle.