Interaction of Alkali Light Chain 1 with the Isolated 20-Kilodalton Fragment of Myosin Subfragment-1 Heavy Chain and F-Actin

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Abstract
The binding of one of the alkali light chains of myosin, Al, with the isolated renatured 20-kDa fragment of myosin subfragment-1 heavy chain was demonstrated by means of difference UV absorption spectroscopy. The difference spectrum with either rabbit or chicken Al showed two characteristic peaks at 279 and 287 nm indicating a perturbation of tyrosyl chromophores by the association with the 20-kDa fragment. The Δ¸ at 287 nm increased with an increase in the molar ratio of Al/20-kDa fragment and reached a maximum value at around equimolar ratio. The maximum Δ¸ value was approximately three times larger with rabbit Al than with chicken Al. Based on the positions of Tyr residues in the amino acid sequences, the contact surface of Al with myosin heavy chain was concluded to be spread over a large area of Al. The binding of 20-kDa fragment with F-actin was measured by following the increase in turbidity. The affinity appeared to increase several times in the presence of Al. Al may possibly control the affinity of myosin for actin.