Actin and Microfilaments

At least six different isoforms of actin have been identified in vertebrate tissues, each encoded by a different gene (Vanderkerckhove and Weber 1978, Reddy et al. 1990). Non-muscle cells contain two general cytoplasmic actins, P and y. They are very similar to each other (only 4 amino acid substitutions) (Vandekerckhove and Weber 1979). Ultrastructural evidence that calponin binds selectively to cytoskeletal actin has led some investiga- 

Monomeric actin is stable in distilled water only. 

Actin has been isolated from alveolar macrophages by Hartwig and Stossel (1975, 1982), Stos-SEL and Hartwig (1975, 1976), and Hartwig et al. (1977). Under the electron microscope, Allison et al. (1971) and Senda et al. (1975) saw arrow heads typical for actin microfilaments with heavy meromyosin. 

Hartwig and Janmey (1989) found that phor-bol 12-myristate 13-acetate would increase the nucleation activity of macrophages washed out of the lungs of New Zealand white rabbits given complete 

Freund s adjuvant intravenously. This increment was completely cytochalasin-sensitive, indicating that exposure to PMA leads to formation of free barbed ends. 

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