The site of paramyosin in insect flight muscle and the presence of an unidentified protein between myosin filaments and Z-line.

The position of paramyosin in insect flight muscle was determined by labelling myofibrils with antibody to paramyosin and examining them by fluorescent and electron microscopy.Antiserum to dung beetle paramyosin had antibodies to another protein as well as to paramyosin. Specific anti-paramyosin bound to the H-zone of Lethocerus myofibrils showing paramyosin was exposed only in that region. Antibodies to the other protein bound at the ends of the A-band.The exposure of antigenic sites in the two regions of the myofibril depended on the extent of contraction in the myofibril: the sites at the end of the A-band were most exposed in rest-length myofibrils and those at the H-zone in shortened ones.Antibody-labelling in stretched bee muscle showed that the protein at the ends of the sarcomere extended from myosin filaments to Z-line.The high resting elasticity of insect flight muscle and hence its capacity for oscillatory contraction may be due to the protein between myosin filaments and Z-line.