Localization of β-Actinin in the Z Lines of Chicken Breast Muscle, as Detected with a Monoclonal Antibody Specific to the βI Subunit (Cap Zα)

Abstract

Immunofluorescence microscopy showed that a monoclonal antibody, 2F3, specific to the βI subunit (Cap Zα) of β-actinin (Cap Z) bound to the Z lines of chicken breast muscle. When myofibrils were briefly extracted with 0.6 M KI, the reactivity of the Z lines with 2F3 was very weak, but on subsequent treatment with purified β-actinin, the antibody binding recovered. β-Actinin inhibited elongation of the actin filaments of isolated I-Z-I brushes, myosin-extracted sarcomeres, on the addition of G-actin. However, when an increased concentration of G-actin was added, the inhibitory action of β-actinin became negligible, suggesting that β-actinin did not cap the pointed end of an actin filament in a myofibril.