The N terminus of myosin light chain 1 (MLC-1) of skeletal muscle bind
to the C terminus of actin. We investigated whether the N termini of
human cardiac MLC-1 isoforms likewise bind to actin. Furthermore, we i
nvestigated whether the N-terminal sequence 5-15 (P5-14) of MLC-1 of h
uman atrium (ALC-1) and ventricle (VLC-1) bind with different affiniti
es to actin. Affinity beads mere produced by covalently coupling a syn
thetic peptide corresponding to the N-terminal sequence 4-14 of human
VLC-1 to aminohexylagarose in order to bind G-actin. We found, that G-
actin specifically binds to the affinity beads. Furthermore, preincuba
tion of G-actin with P5-14 of both ALC-1 and VLC-1 decreased the amoun
t of G-actin recovered from the affinity beads in a concentration-depe
ndent manner. The half-maximal effective concentrations, however mere
significantly (p < 0.01) different being 0.32 +/- 0.02 mu M and 0.71 /- 0.02 mu M for the VLC-1 and ALC-1 peptide, respectively. The approp
riate scrambled peptides mere without effect up to 3 mu M These result
s demonstrate the specific interaction between the N-terminal domains
of human cardiac MLC-1 isoforms and actin and reveal different actin a
ffinities of MLC-1 isoforms. Weak binding of ALC-I to actin could expl
ain the higher cycling kinetics of cross-bridges with ALC-1 compared t
o those with VLC-1. (C) 1997 Federation of European Biochemical Societ
ies.