A possible role for myosin light chain 1 slow of bovine muscle.

Myosin light chain 1 slow (LC1slow) was purified from the bovine slow-twitch muscle masseter and used as an antigen in chicken. The antibody fraction from egg yolk was employed to show the distribution of LC1slow in samples of diverse bovine muscles. Adjacent cryosections were cut. One section was stained for myofibrillar adenosine triphosphatase (ATPase) activity and the other was challenged with the antibody fraction, followed by a fluorescently-labelled secondary antibody. The ATPase section (viewed with conventional optical microscopy) displayed fast and slow fibres, whereas the antibody-labelled section (viewed with epifluorescent optics) showed which of the slow fibres contained LC1slow. In some of the muscles examined, the slow fibres contained variable amounts of LC1slow. In other muscles, such as those involved in chewing, the slow fibres were all rich in LC1slow. Slow fibres in yet other muscles, for example deep hip muscles and an extraocular muscle, were devoid of LC1slow. Based on the probable functions of the muscles examined, the hypothesis is advanced that LC1slow is associated with movement, its absence from slow fibres signifying a postural role for those slow fibres. The present work also documents the LC1slow content and muscle fibre composition of 14 hind leg muscles of a single ox. The results suggest postural and locomotory roles for certain muscles.