[Investigation of rat brain prealbumins]

12 prealbumines of rat brain water-soluble fraction were studied. Neither lipid components nor carbohydrate ones were found out in the proteins. Three of the proteins appeared to be RNA-proteids. Their subcellular distribution was investigated. The effects of temperature, salts, acids and ethanol on disc electrophoretic spectrum of brain prealbumines were closely observed. The amino acid composition, properties, compartmentation, tissue and species specificity of one of the prealbumines were studied in detail. The protein is marked as BTB-protein, as it migrates under disc electrophoresis in 7,5% polyacrylamide gel with the "witness" front of bromothemol blue (BTB). The content of BTB-protein is 0.06--0.08 gr per 100 gr of wet tissue. The protein is RNA-proteid. Its molecular weight is 10,000--20,000. BTB-protein contains 42 mole % of acidic amino acids and 5.4 mole % of alkaline ones. The protein was found in nuclear and cytoplasmic fractions. It is mainly an all-organs protein. Small amount of this protein is found in blood serum. BTB-protein can be found on the disc electrophoregramms of embryo and newborn rats brain proteins, as well as of the brain of other mammals, birds and amphibia. BTB-protein is resistant to boiling and to the effects of salts, acids, ethanol. It is suggested that BTB-protein has heterogenous structure and may be of neurophysin nature.