Isoniazid inhibition of liver glutamic oxaloacetic transaminase from the goat Capra hircus

1. 1. Glutamic oxaloacetic transaminase (EC 2.6.1.1), has been prepared from the liver of Hausa he-goat ( Capra hircus). 2. 2. Gel filtration of the liver extract presents evidence of two molecular species of the enzyme; one species (Fraction A) has a specific activity of 280 U/mg protein and the other (Fraction B) has a specific activity of 338 U/mg protein. 3. 3. Fraction A has optimum activity at pH 6.8 and Fraction B is optimally active at pH 5.5. The observed variation in activity with pH variation may be due to ionisation of some group(s) on the enzyme. 4. 4. Characteristic spectral changes typical of INH/GOT interactions at low and high pH values are presented. 5. 5. Typical Dixon's plot indicates a competitive inhibition of the enzyme by INH. K i, and K m of 0.04 and 2.5 mM for Fraction A and K i and K m of 0.098 and 4.7 mH for Fraction B have been calculated from the data. 6. 6. These results have been discussed in the light of the properties of the enzyme from other sources.