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The in vivo effects of phenobarbital on 32 P incorporation into rat liver acidic nuclear proteins were studied. Nuclei were isolated in citric acid and the acidic nuclear proteins were extracted with phenol. Electrophoretic fractionation of these proteins was achieved on 10% acrylamide gels containing 0.1% sodium dodecylsulfate at pH 7.2. A stimulation of 32 P incorporation into acidic nuclear proteins was observed within 2–6 h after administration of drug. A maximum, 48% greater than control level, was observed at 24 h after treatment. The electrophoretic profiles of the incorporated 32 P indicated that the stimulation may be selective for specific acidic nuclear proteins; however, the phosphorylation of all the acidic nuclear phosphoproteins seems to be stimulated to some degree. These results suggest that phosphorylation of acidic nuclear proteins may play a role in the effects of phenobarbital on liver growth or microsomal enzyme activity.

Reducing agents are commonly used to limit aggregation of acidic nuclear proteins in aqueous media. However, these agents interfere with protein determinations and thus make it difficult to continuously monitor protein concentration. In this study, acidic nuclear proteins were alkylated with iodoacetamide to eliminate the need for a reducing agent. The alkylated proteins can be easily analyzed; and furthermore, alkylation may enhance the resolution obtained by column chromatography or gel electrophoresis.