FORMATION OF ARROWHEAD COMPLEXES WITH HEAVY MEROMYOSIN IN A VARIETY OF CELL TYPES

TLDR

Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments that can be readily visualized in sectioned muscle. The study examines the significance of HMM‑filament binding given that arrowhead complexes appear in cell types not normally thought to contain actin filaments. HMM binds actin filaments to form arrowhead complexes in a variety of cells—including fibroblasts, chondrogenic, nerve, epithelial, and metaphase cells—while showing no interaction with microtubules, tonofilaments, membranes, nuclei, or collagen fibrils.

Abstract

Heavy meromyosin (HMM) forms characteristic arrowhead complexes with actin filaments in situ. These complexes are readily visualized in sectioned muscle. Following HMM treatment similar complexes appear in sectioned fibroblasts, chondrogenic cells, nerve cells, and several types of epithelial cells. Thin filaments freshly isolated from chondrogenic cells also bind HMM and form arrowhead structures in negatively stained preparations. HMM-filament complexes are prominent in the cortex of a variety of normal metaphase and Colcemid-arrested metaphase cells. There is no detectable binding of HMM with other cellular components such as microtubules, 100-A filaments, tonofilaments, membranes, nuclei, or collagen fibrils. The significance of HMM-filament binding is discussed in view of the finding that arrowhead complexes form in types of cells not usually thought to contain actin filaments.