Immunohistochemical localization of dipeptidyl aminopeptidase IV in rat kidney, liver, and salivary glands

Specific antibodies directed against dipeptidyl aminopeptidase (DAP) IV prepared from rat and pig kidneys were produced in rabbits. Using a peroxidase-labeled or fluorescein isothiocyanate-labeled antibody method, localization of DAP IV was investigated in various tissues of the rat (kidney, liver and salivary glands). DAP IV was mainly localized in the brush border of the proximal tubules (kidney), in the cell membrane around bile canaliculi of hepatic cells (liver), and in the cell membrane of serous acinar cells (parotid and submaxillary glands). These results substantiate that DAP IV is a membrane-bound peptidase.

Comparison of dipeptidyl peptidase IV prepared from pig liver and kidney

Dipeptidyl peptidase IV (dipeptidylpeptide hydrolase, EC 3.4.14.-) has been purified from the microsomal fraction of pig liver, using an immunoaffinity chromatography, and its properties compared with those of the enzyme purified from pig kidney. The amino acid compositions of both enzymes were similar. The same kinds of carbohydrates were found in both enzymes, but there were differences in the molar concentrations of individual sugars. The liver enzyme had greater concentrations of mannose, fucose and sialic acid than the kidney enzyme, while the concentrations of galactose and glucosamine were greater in the kidney enzyme. The carbohydrates accounted for approx. 18.3 and 22.7% of the weight of the kidney and liver enzymes, respectively. The pH optima, molecular weights, substrate specificities and Km values of the two enzymes and the effects of diisopropylfluorophosphate on their activities were nearly identical. The liver enzyme was heat- and pH-sensitive, but not attacked by proteinases.

Immunohistochemical localization of dipeptidyl aminopeptidase (DAP) IV in the rat submandibular gland during postnatal development

The localization of dipeptidyl aminopeptidase (DAP) IV in the rat submandibular gland during postnatal development was studied immunohistochemically using the unlabeled antibody enzyme method. Cryostat sections of rat submandibular glands were examined in animals 1 to 50 days old. In the first postnatal week, faint immunoreaction was detected in the apical region of the cytoplasm of terminal tubules. During the second postnatal week the reaction was gradually restricted to the luminal region of terminal tubules or developing acinar cells, and its intensity increased. The most striking change of the enzyme localization was observed in 15-day-old rats. At this time, DAP IV was confined to the luminal and lateral membranes of differentiated acinar cells and to the luminal membranes of intercalated and striated duct cells. This localization pattern was similar to that of the adult animal. DAP IV activity in the gland was also measured biochemically during the postnatal development. The results were in agreement with those of the immunohistochemical study. These results suggest that the localization of DAP IV is closely related to the postnatal differentiation and proliferation of acinar cells.

Identification and quantification of alpha-amino adipic acid in bovine dentine phosphoprotein

A unique phosphoprotein, which contains an uncommon amino acid, alpha-amino adipic acid (alpha-AAA), was isolated from unerupted bovine teeth by extensive EDTA demineralization. The alpha-AAA in the protein hydrolysates was identified based on the elution time on an amino acid analyzer using the sodium and lithium citrate buffer in a dual column system, and its identity was confirmed by comparisons of its DNS derivative with that of authentic alpha-AAA. This result suggests that the lysine residues in the phosphoprotein may be deaminated by an amine oxidase into allysine and further oxidized to alpha-AAA.

Immunochemical identity of dipeptidyl aminopeptidase IV from pig serum, liver, submaxillary gland and kidney

The enzymes which were extracted by autodigestion from the microsomal fractions of the pig kidney, liver and submaxillary gland and from the serum showed an immunochemical identity by a double immunodiffusion test. But the kidney enzyme had a different pI-value from the pI-values of the enzymes of other organs.

Successive cleavage of N-terminal Arg1--Pro2 and Lys3-Pro4 from substance P but no release of Arg1-Pro2 from bradykinin, by X-Pro dipeptidyl-aminopeptidase

X-Pro dipeptidyl-aminopeptidase (EC 3.4.14.1) purified homogeneously from the human submaxillary gland was proved to hydrolyze N-terminal dipeptide Arg1-Pro2 and subsequent dipeptide Lys3-Pro4 from substance P (Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-gly-Leu-Met-NH2). Km and V values of hydrolysis of substance P were 2.0 mM and 3.6 mumol/min per mg protein, respectively. In contrast, the N-terminal Arg-Pro of bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) was not cleaved by the enzyme.

Dipeptidyl aminopeptidase IV, a glycoprotein from pig kidney

Dipeptidyl aminopeptidase IV was purified 350 fold from pig kidney by chromatographic procedures including affinity chromatography with conjugates of Gly-Pro linked to Sepharose 4.B. Purified enzyme existed in a dimeric form as determined by sodium dodecyl sulfate polyacrylamide-gel electrophoresis using dimethyl suberimidate (a cross-linking reagent). The molecular weight of the subunit was estimated to be 100 000 by gel filtration with 6 M guanidine hydrochloride and to be 94 000 based on analysis of N-terminal residue (dinitrophenyl-serine). The amino acid composition of the purified enzyme was also determined. The enzyme contained 18.3% of carbohydrate consisting of mannose, galactose, fucose, glucosamine and sialic acid. The enzyme desialized with sialidase was found to still possess full enzyme activity.