Crithidia fasciculata tyrosine transminase : I. Development, characterization and differentiation from alanine transminase

Abstract

1. 1. Considerable tyrosine transminase ( L-tyrosine: 2-oxoglutarate aminotransferase, EC 2.6.1.5) activity was found to be present in both the soluble and particulate cell fractions of the kinetoplastid Crithidia fasciculata. 2. 2. Pyridoxal phosphate activates the soluble form of tyrosine transminase over 4-fold and α-ketoglutarate over 2-fold; α-ketoglutarate increases too the degree of conjugation of the enzyme with the coenzyme. 3. 3. Tyrosine transminase is differentiated on the basis of its properties and development from alanine transminase activity in the soluble cell fraction. 4. 4. Its activity rises transiently at the beginning and again after the end of the logarithmic phase of growth, attaining levels 20–30 times as high as in normal rat liver. 5. 5. At the end of the stationary phase of growth, tyrosine transminase activity practically dissapears from the soluble fraction and increases in the insoluble cell fraction. This process is paralleled by active haemin accumulation in the particulate cell fraction.