Aminopeptidases and Dipeptidyl Peptidases Activities in Chicken Bone Tissue.

Abstract

There have been very few papers reporting on the localizations of aminopeptidases and dipeptidyl peptidases activities in bone tissue, although these peptidases seem to have important roles in bone resorption and osteoid degradation. The present study demonstrates these peptidases in fixed and decalcified tibial metaphyses of 3-week-old chickens using the azo-dye methods at light microscopic level. As substrates, amino 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 aminopeptidase-A (AP-A, EC 3.4.11.7), Gly-Arg-MNA for dipeptidyl peptidase-I (DPP-I, EC 3.4.14.1), Lys-Ala-or Lys-Pro-MNA for dipeptidyl peptidase-II (DPP-II, EC 3.4.14.2), and Gly-Pro-MNA for dipeptidyl peptidase-IV (DPP-IV, EC 3.4.14.5). An AP-M in osteoclasts, and APA in osteoblasts and osteocytes were observed. These activities were sensitive to 10 mM of ethylenediaminetetraacetic acid (EDTA). A DPP-I was seen in osteoclasts, osteoblasts and osteocytes in the presence of mercaptoethylamine (MEA), however Gly-Arg-MNA hydrolyzing activity in the absence of MEA was restricted to only osteoclasts. DPP-II activity was present in osteoblasts and osteocytes, using Lys-Pro-MNA as a substrate. There was no Lys-Ala-MNA hydrolyzing activity in bone cells. The present study failed to demonstrate DPP-IV activity in either 4% paraformaldehyde- or 2.5% glutaraldehyde-fixed samples, although it was observed in the glomerulus and proximal convoluted tubule cells of the rat kidney fixed with glutaraldehyde. The present study suggests that AP-M and DPP-I in osteoclasts, and AP-A, DPP-I and DPP-II in osteoblasts seem to function in the bone remodeling process.