Role of hydrolysis in the association of leu-enkephalin to peripheral blood mononucleate cells.
The possible hydrolysis of labelled leucine enkephalin in the presence of peripheral blood mononucleate cells and its association with the same cells have been investigated. Results obtained indicate that under experimental conditions leu-enkephalin is rapidly hydrolysed in the presence of model cells. Under the same conditions, the radioactive label is partially associated with the cells. The presence of protease inhibitors reduces both enkephalin degradation and association of the radioactive label with the cells. The hypothesis that the associated species is intact leu-enkephalin is not supported by the relative kinetics of enkephalin hydrolysis and of association of the radioactive label with the cells, nor by the statistically significant correlation between these data, nor again by the effect of proteolysis inhibitors. The same data agree with the hypothesis that the radioactive label associated with the cells is represented by one, or several, of the fragments formed by enkephalin hydrolysis, not by the intact molecule. However, results obtained in the presence of hydrolysis-stable DADL indicate association with the cells of the intact peptide. Moreover, antigen stimulation has opposite effects on the two peptides: with leu-enkephalin, hydrolysis and association are increased, with DADL association is decreased by stimulation. The sum of these data seems to suggest the co-existence in PBMC of two phenomena, i.e. internalization of one, or several, of the fragments formed by the enzyme degradation of enkephalin and binding to membrane receptors of the intact pentapeptide.
Urbani
A
A
Dipartimento di Medicina Sperimentale e Scienze Biochimiche, II Università degli Studi di Roma Tor Vergata, Italy.
Bongiorno
L
L
Ausiello
C M
CM
Marini
M
M
Roda
L G
LG
D002478:Cells, Cultured; D004743:Enkephalin, Leucine / Q000378:metabolism*; D016308:Enkephalin, Leucine-2-Alanine / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D007963:Leukocytes, Mononuclear / Q000378:metabolism*; D010835:Phytohemagglutinins; D011480:Protease Inhibitors / Q000494:pharmacology
D010835:Phytohemagglutinins; D011480:Protease Inhibitors; D004743:Enkephalin, Leucine; D016308:Enkephalin, Leucine-2-Alanine