Amino acid metabolism of growing tissues: II. Alanine-glutamic acid transaminase activity of embryonic rat liver

Abstract

1. 1. In embryonic liver 55 per cent of the alanine-glutamic acid transaminase activity resided in the mitochondrial fraction and 27 per cent in the supernatant fraction. In adult liver on the other hand only 20 per cent of the total transaminase activity was present in the mitochondrial fraction and 62 per cent in the supernatant. 2. 2. The ratio QT glutamic acid formation/QT alanine formation of the nuclear, mitochondrial and microsomal fractions of both embryonic and adult liver was considerably greater than 1. This ratio approximated 1 in the supernatant fractions of both embryonic and adult liver. 3. 3. It was shown by two independent methods that the transaminase activity of the supernatant fraction of adult liver was not due to solubilization of mitochondrial enzyme. 4. 4. In whole homogenates of 16-day-old embryonic liver the rate of the forward reaction (glutamic acid formation) was considerably greater than that of adult liver homogenates. On the other hand the reverse reaction (alanine formation) proceeded at a lower rate in embryonic liver homogenates. 5. 5. The significance of the characteristic QT glutamic acid formation/QT alanine formation ratio of embryonic and adult liver is discussed in terms of the subcellular distribution of alanine-glutamic acid transaminase.