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The nuclear content of conjugated polyamines increased during rat liver regeneration. Conjugated polyamines isolated from the acid-precipitable fraction of nuclei required peptide bond hydrolysis for release of the parent compounds. The most striking change occurred in conjugated putrescine which fluctuated in a biphasic manner; maximal nuclear levels 12-fold and 25-fold above those of sham-operated controls were achieved at 4 and 42 hr after hepatectomy, respectively. Conjugated spermidine and spermine increased 3- and 2-fold respectively within 4 hr and remained high throughout the 48 hr studied. When expressed on the basis of mg of nuclear protein, the maximal conjugated putrescine increased 19-fold, conjugated spermidine increased 2-fold, and conjugated spermine decreased by 50%. Therefore, the spermidine and spermine conjugates may be of a more constitutive nature whereas the large changes in the nuclear conjugation of putrescine associated with the onset of growth may play a regulatory role. The nucleus also contained transglutaminase (R-glutaminyl-peptide:amine gamma-glutamyl-yltransferase, EC 2.3.2.13), an enzyme shown in vitro to conjugate polyamines covalently to proteins. The specific activity of the nuclear enzyme increased rapidly after partial hepatectomy to a level 3-fold above control at 4 hr and 7-fold above control at 42 hr. The increased conjugating activity resulted from an increase in detectable maximal velocity and not a change in affinity of the enzyme for putrescine (Km congruent to 0.4 mM). There was also a 3-fold increase at 42 hr in the number of nuclear amine acceptor sites present to which radiolabeled putrescine could be conjugated by endogenous enzyme.

Increased nuclear conjugated polyamines and transglutaminase during liver regeneration.