Increased nuclear conjugated polyamines and transglutaminase during liver regeneration.
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.
D000818:Animals; D002467:Cell Nucleus / Q000378:metabolism*; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008115:Liver Regeneration; D008297:Male; D011073:Polyamines / Q000378:metabolism*; D011700:Putrescine / Q000378:metabolism; D051381:Rats; D013095:Spermidine / Q000378:metabolism; D013096:Spermine / Q000378:metabolism; D005723:gamma-Glutamyltransferase / Q000378:metabolism*
D011073:Polyamines; D013096:Spermine; D005723:gamma-Glutamyltransferase; D013095:Spermidine; D011700:Putrescine