Marginal involvement of pyroglutamyl aminopeptidase I in metabolism of thyrotropin-releasing hormone in rat brain.
On thyrotropin-releasing hormone (TRH) metabolism, pyroglutamyl aminopeptidase II (PAP-II), a zinc-dependent ectoenzyme primarily located in the central nervous system, is believed to play a predominant role. Recently we cloned pyroglutamyl aminopeptidase I (PAP-I) which is known for specifically removing a L-pyroglutamate (L-pGlu) residue from the amino terminus of proteins and peptides including TRH. To investigate possible contribution of PAP-I toward TRH metabolism, we conducted biochemical and immunohistochemical characterization using recombinant rat, mouse and human PAP-Is and an antibody raised against rat PAP-I. The Km values toward TRH by the recombinant PAP-Is were about 0.05 mM, being similar value to the reported value of recombinant PAP-II. The L-pGlu-cleaving activities toward TRH in rat brain homogenate were inhibited by a PAP-II specific inhibitor 1,10-phenanthroline, but not inhibited by the antibody against rat PAP-I. Immunohistochemical study in rats revealed heterogeneous distribution of PAP-I in the pituitary, the target tissue of TRH, but the distribution was cytosolic. Taken together, these results suggested that PAP-I might not be dominantly involved in the degradation of TRH in rats. Additionally, we found that PAP-I was localized in the renal proximal tubules. Further investigations are needed for elucidating the function of PAP-I in these restricted sites.
Abe
Koji
K
Drug Metabolism and Pharmacokinetics Research Laboratories, Sankyo Co., Ltd, Tokyo, Japan. koumia@sankyo.co.jp
Fukuda
Kuniaki
K
Tokui
Taro
T
D000626:Aminopeptidases / Q000378:metabolism*; D000818:Animals; D001921:Brain / Q000201:enzymology / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007150:Immunohistochemistry; D008297:Male; D051381:Rats; D011916:Rats, Inbred F344; D013347:Subcellular Fractions / Q000201:enzymology / Q000378:metabolism; D013973:Thyrotropin-Releasing Hormone / Q000378:metabolism*
D004791:Enzyme Inhibitors; D013973:Thyrotropin-Releasing Hormone; D000626:Aminopeptidases; C497676:pyroglutamyl aminopeptidase I, rat