Summary
The saline-soluble proteins of rat liver nuclei have been extensively resolved into profiles according to charge, permitting comparison with similar arrays from liver cytoplasm.
Nuclei were isolated in 2.1 m sucrose solution from the perfused livers of rats fed stock, control, or hepatocarcinogenic 3′-methyl-4-dimethylaminoazobenzene diet. After feeding the azo dye for 20 days, the nuclei contained 3% of the bound azo dyes of liver. Exhaustive extraction of the nuclei in isotonic saline-phosphate buffer at pH 7.4 dissolved approximately 49% of the nitrogen and 86% of the protein-bound dyes.
Fifteen classes of the soluble nuclear macromolecules, formerly designated on the basis of free boundary electrophoresis, were isolated by column zonal electrophoresis. The strongly acidic, weakly acidic, and near-neutral Classes 2–15 consist of proteins. In contrast, the basic Classes 16–18 are composed of small molecules, apparently dissociated from macromolecules. Approximately one-half of the protein-bound dyes in the charge profiles are associated with a small class of near-neutral proteins, Class 14. The remainder are combined mainly with the acidic proteins, Classes 5–9.
The saline-soluble proteins isolated from liver nuclei generally appear to be similar to those of cytoplasm. This appears to apply particularly to the principal near-neutral azoproteins of the nucleus (Class 14) and those of the cytoplasm (slow h2). Conjecturally, these soluble macromolecules may be shared throughout the “soluble space” of the cell.
This investigation was supported in part by USPHS Grants CA-05945, CA-06927, and FR-05539 from the National Cancer Institute and an appropriation from the Commonwealth of Pennsylvania. This paper was presented in part at the 57th Annual Meeting of the American Association for Cancer Research, Denver, Colorado, May 26–28, 1966 (4).
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