The actin content of fibroblasts

Abstract

Cultures of chick skin fibroblasts were dissolved in solutions of sodium dodecyl sulphate, and their entire protein content was examined by gel electrophoresis. The most abundant species migrated in the same position as muscle actin. It gave a similar pattern of iodinated peptides after reaction with radioactive sodium iodide and digestion with proteinases, and contained comparable amounts of N-methylhistidine. Its amount was estimated by quantitative densitometry of stained gels with bovine serum albumin as an internal standard, and by radioactive assay ofcultures that had been grown in the presence of [35S]methionine. The values obtained ranged from 7 to 14% of the total cellular protein, with an average of 8.5 %. A protein band in the position of muscle myosin was also present and accounted for about 2.5 % of the total protein. Both this and the actin band increased in relative amount with the age of the cultures.

Isolation and Characterization of Profilactin and Profilin from Calf Thymus and Brain

“…Bray and Thomas determined that as much as 50 % of the actin in extracts of brain is in a non-filamentous form under a variety of extraction conditions [36,37]. Recently we determined that in extracts of suspension cultured lymphocytes (cell line DG-75) as much as 60-65 o/, of the actin is in an unpolymerized form [39].…”

Relationships between Actin Regulatory Mechanisms and Measurable State Variables

“…Biochemically, it can be measured by comparing the quantity of actin that resists triton extraction to total cellular actin. 6 The fluorescence-based methods of FRAP and PAF can also be used to estimate the polymer fraction. In FRAP, fluorescently derivatized actin is introduced to cells either through microinjection or expression, and a laser is used to rapidly photobleach a region of the cell.…”

“…6 This is made possible in many cells by the sequestering protein thymosin b4, which binds in a 1:1 complex with monomers and prevents their assembly into filaments. Thymosin b4 inhibits nucleotide exchange on bound monomers, but also has a 100-fold higher affinity for ATP-bound monomers than ADP-bound monomers, and therefore generally binds monomers after they have exchanged ADP for ATP.…”

Localization of [alpha]-actinin and tropomyosin in muscle and nonmuscle systems

“…All the Pq-SO crude a-actinin fractions also contained sizable quantities of a 42,000-dalton polypeptide that migrated at the same rate as actin (Figure 67). Previous studies have shown that fibro blasts (Bray and Thomas, 1975;Perdue, 1973;Yang and Perdue, 1972) and brush borders (Tilney and Mooseker, 1971) contain actin. The Pq-SQ crude a-actinin fractions from brush borders and fibroblasts also contain and small amounts of a 30,000-dalton polypeptide that may be tropomyosin (Figure 67).…”

“…Because both actin (Bray and Thomas, 1975;Perdue, 1973;Yang and Perdue, 1972) and myosin (Adelstein et , 1972;Ostlund et al , 1974) have been purified from fibroblasts, it seems likely that the 42,000…”