The nucleoprotein content of fibroblasts growing in vitro

Abstract

Growth in vitro of chick heart fibroblasts was meas-ured by increases in the nucleoprotein phosphorus (NPP). Chick embryo extract had a greater growth promoting power than sheep embryo extract at same N content. The activity of tissue extracts is impaired by procedures which denature proteins. Increased activity results from defatting the ex-tracts by freezing with ether. Defatted extracts are further improved by drying from the frozen state, which was the only satisfactory drying procedure for all extracts. Use of filter candles was obviated by sterilizing the extracts with benzene or ether. Sheep embryo extracts retained growth-promoting activity when stored at [long dash]30[degree] for 9 mos. in sterile state. The growth-promoting activity is not attributed to any organ or tissue. Ethanol precipitates of the embryonic extracts were more active than the same preparations from adult sheep heart. A nucleoprotein prepared from sheep embryo extract was effective in low concs. Solns. of histone in low concs. accentuated the effect of embryo extract on the NPP of fibroblasts.