Modification of Pepsinogen with Pyridoxal Phosphate
1974; Elsevier BV; Volume: 249; Issue: 23 Linguagem: Inglês
10.1016/s0021-9258(19)81263-2
ISSN1083-351X
Autores Tópico(s)Glycosylation and Glycoproteins Research
ResumoPyridoxal-PO4 binds to pepsinogen in a reaction in which the stoichiometry is highly dependent on the conformation of the protein. When pepsinogen is in its native conformation, pyridoxal-PO4 forms Schiff bases with the α-NH2 group of Leu1 and the e-NH2 group of Lys358. When the protein is mildly denatured and assumes a more extended conformation, pyridoxal-PO4 can react with the e-NH2 groups of approximately 3 other lysine residues present in the NH2-terminal region of the pepsinogen molecule. Pepsinogen with pyridoxal-PO4 covalently attached at Leu1 and Lys358 by reduction of the protein-pyridoxal-PO4 Schiff bases can be activated to pepsin. This modified pepsin, which has a pyridoxal-PO4 molecule covalently attached to the e-NH2 group of its sole lysine residue, cannot be distinguished catalytically from the unmodified enzyme. As soon as 1 or 2 of the lysine residues in the NH2-terminal region of pepsinogen become modified with pyridoxal-PO4, the zymogen can no longer be activated, possibly because the protein cannot assume the proper conformation required for activation. No pattern to the sequence of pyridoxal-PO4 incorporation into pepsinogen was observed after the first 2 pyridoxal-PO4 molecules were incorporated. The lysine residues showing the greatest reactivity toward pyridoxal-PO4 other than Lys358 were found in regions of the NH2 terminus in which the density of basic amino acids was highest.
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