The effect of zinc salts, zinc chloride and zinc sulfate on the structure and ATPase enzyme activity of actomyosin from pelagic fish (Sardinella longiceps) has been investigated. ATPase enzyme activity decreased in the presence of both the zinc salts. The inhibitory effect is present in both pH of 7.0 and 9.0. At concentration of 1 x 10(-3) M of zinc salts, complete inhibition of ATPase enzyme activity is observed. With the increase in temperature from 25 degrees C to 45 degrees C the ATPase activity decreased by nearly 80%. The solubility profile of actomyosin in the presence of zinc salts shows a sigmoid pattern as the concentration of both the zinc salts increases. Free SH content of actomyosin decreased with the increase in concentration of zinc salts. Intrinsic fluorescence indicated significant decrease in relative fluorescence intensity of actomyosin. This indicates significant alterations in the structure of actomyosin. Analysis of secondary structure also indicates significant alteration in the alpha-helical content upon binding of both zinc salts. (C) 2009 Elsevier Ltd. All rights reserved.