부산대학교 도서관

This study was designed to investigate a postulated relationship between vitamin B-12 and leucine metabolism in mature domestic chickens. Plasma amino acid analysis revealed the presence of β-leucine at a concentration of 60 to 80 µmol/l. After 425 d on a vitamin B-12-deficient diet, plasma β-leucine was 133% higher (P< 0.06) and plasma leucine and methionine lower (P< 0.03) than values in plasma from hens fed a diet adequate in vitamin B-12. Branched-chain-amino-acid aminotransferase (EC 2.6.1.42) (BCAT) activity was not enhanced by vitamin B-12 deprivation (P> 0.05). In contrast to leucine, β-leucine was not utilized as substrate by BCAT for the formation of α-ketoisocaproate. Kidney extracts possessed leucine 2,3-aminomutase (EC 5.4.3.7) (LAM) activity, as evidenced by enhanced conversion of β-leucine to β-leucine in the presence of adenosylcobalamin. LAM activity could not be demonstrated in liver or muscle extract, while leucine formation by pancreas extract was negligible. These data represent the first evidence of the presence of the amino acid β-leucine in chicken plasma. In addition, the data support vitamin B-12-dependent leucine synthesis from β-leucine in the chicken and highlight the kidney's role in leucine synthesis.