AMINOPEPTIDASES AND DIPEPTIDYL PEPTIDASES ACTIVITIES IN CHICKEN BONE TISSUE

There have been very few papers reporting on the localizations of amin opeptidases and dipeptidyl peptidases activities in bone tissue, altho ugh these peptidases seem to have important roles in bone resorption a nd osteoid degradation. The present study demonstrates these peptidase s in fixed and decalcified tibial metaphyses of 3-week-old chickens us ing the ate-dye methods at light microscopic level. As substrates, ami no acid derivatives of 4-methoxy-2-naphthylamine (MNA) were used: Leu- or Ala-MNA for aminopeptidase-M (AP-M, EC 3.4.11.2), Glu-MNA for amin opeptidase-A (AP-A, EC 3.4.11.7), Gly-Arg-MNA for dipeptidyl peptidase -I (DDP-I, EC 3.4.14.1), Lys-Ala- or dipeptidyl peptidase-ll (DPP-II, EC 3.4.14.2), and Gly-Pro-WNA for dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5). An AP-M in osteoclasts, and AP-A in osteoblasts and osteocy tes were observed. These activities were sensitive to 10 mM of ethylen ediaminetetraacetic acid (EDTA). A DPP-I was seen in osteoclasts, oste oblasts and osteocytes in the presence of mercaptoethylamine (MEA), ho wever Gly-Arg-MNA hydrolyzing activity in the absence of MEA was restr icted to only osteoclasts. DPP-II activity was present in osteoblasts and esteocytes, using Lys-Pro-MNA as a substrate. There was no Lys-Ala -MNA hydrolyzing activity in bone cells. The present study failed to d emonstrate DPP-IV activity in either 4% paraformaldehyde- or 2.5% glut araldehyde-fixed samples, although it was observed in the glomerulus a nd proximal convoluted tubule cells of the rat kidney fixed with gluta raldehyde. The present study suggests that AP-M and DPP-I in osteoclas ts, and AP-A, DPP-I and DPP-II in osteoblasts seem to function in the bone remodeling process.