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Aminopeptidase N Gene Expression and Abundance in Caprine Mammary Gland is Influenced by Circulating Plasma Peptide

¹ Department of Animal Sciences, Faculty of Agricultural, Food and Environmental Quality Sciences, and
² The Koret School of Veterinary Medicine, The Hebrew University of Jerusalem, PO Box 12, Rehovot, Israel
³ Agricultural Research Organization, Volcani Center, Institute of Animal Science, Bet Dagan, Israel

Corresponding author: S. J. Mabjeesh; e-mail: Mabjeesh{at}agri.huji.ac.il.

This study examined the localization and the effect of circulating peptides on the expression of aminopeptidase N (EC 3.4.11.2) in caprine mammary gland. Four lactating goats in mid to late lactation were used in a crossover design and were subjected to 2 dietary treatments. Abomasal infusion of casein hydrolysate was used to increase the concentration of peptide-bound amino acid in the circulation. Samples of mammary gland tissue from each goat were taken by biopsy at the end of each treatment period to measure gene and protein expression of aminopeptidase N in the tissue. There were no measurable effects on feed intake and milk production for any of the treatments. Western blot analysis showed that aminopeptidase N is located on the basolateral side of parenchymal cells and not on the apical membranes. Abomasal infusion of casein hydrolysate caused a marked change in the profile of arterial blood free amino acids and peptide-bound amino acids smaller than 1500 Da. Abundance of aminopeptidase N mRNA and protein increased by 51 and 58%, respectively, in casein hydrolysate-infused goats compared with the control treatment. It was concluded that aminopeptidase N is one candidate actively involved in the mammary gland to support protein synthesis and milk production. In accordance with the nutritional conditions in the current experiment, it is suggested that aminopeptidase N expression is partly controlled by the metabolic requirements of the gland and postabsorptive forms of amino acids in the circulation.

Key Words: mammary gland • aminopeptidase N • peptide

Abbreviation key: AP = alkaline phosphatase, APN = aminopeptidase N, CAS20 and CAS40 = casein hydrolysate infusions providing an additional 20 and 40% MP, respectively, CAS30 = casein hydrolysate infusion replacing 30% of MPI, FAA = free amino acid, -GT = -glutamyl transpeptidase, MP = metabolizable protein, MPI = metabolizable protein intake, PBAA = peptide-bound AA, PMV = plasma membrane vesicles.

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