Lysine catabolism in pig tissues

Abstract

The primary pathway of lysine degradation in pigs presumably depends on the bifunctional protein α‐aminoadipate δ‐semialdehyde synthase (AASS) which contains lysine α‐ketoglutarate reductase (LKR) and saccharopine dehydrogenase (SDH) activities. In liver, AASS is restricted to the mitochondrial matrix and lysine is transported, presumably, by one or both mitochondrial ornithine transporters (MOT1/MOT2). Lysyl oxidase (LylOx) may represent a minor pathway of lysine oxidation. We assessed LKR, SDH and LylOx activities, lysine oxidation, mRNA abundance of LKR and MOT1/2 and AASS protein abundance (via SDH antibody) in liver, heart, kidney medulla and cortex, enterocytes, triceps and longissimus. In growing pigs (n=5), tissues oxidized lysine at varying rates. LKR activity was highest in liver (P<0.05). LKR mRNA abundance in liver was 6 to 130‐fold greater than other tissues (P<0.05). No differences in SDH activity across tissues were detected. No AASS protein could be detected in muscle. LylOx activity was highest in muscle. MOT1 and 2 were detected in every tissue, although no differences were detected as a function of tissue; interestingly there was a significant correlation between LKR activity and MOT1 mRNA abundance (P<0.05, R2= 0.48). These data indicate that extra‐hepatic tissues contribute to lysine oxidation as do enzymes other than LKR. (Support; HATCH WVA 470)