Rapid increase of profilin-like proteins during liver development.

Extraction of the cytoplasm of rat liver with 5% PCA and subsequent TCA (20%) treatment resulted in the recovery of only a few proteins, the predominant one having an apparent molecular weight of 12K. This 12K protein increased sharply (9-fold) between 2 weeks and 10-20 weeks and then decreased until at least 2 years after birth. 12K protein was separated into two components, 12K-1 (larger) and 12K-2 (smaller), by gel chromatography which had similar amino acid compositions to those of profilin (from Acanthamoeba and hog thyroid). Like profilin, 12K-1 protein inhibited the rate of actin polymerization, while 12K-2 protein did not. These findings suggest that liver profilin-like proteins increase sharply during development.