Tyrosine decarboxylase catalyzes the removal of the carboxyl group from tyrosine to produce tyramine and carbon dioxide. Pyridoxal 5'-phosphate is a necessary coenzyme. By utilizing the apoenzyme (TYDAPO), prepared from cells grown on a vitamin B6 deficient medium, pyridoxal phosphate may be determined. Decarboxylation of radio-labeled tyrosine has permitted the determination of much smaller amounts of pyridoxal phosphate.
Acetone-dried cells were used as the source in a relatively simple extraction and purification of the apoenzyme. The holoenzyme may be used to determine tyrosine, phenylalanine and dihydroxyphenylalanine either manometrically or colorimetrically. Tashian (1957) has reported a determination of tyrosine in urine based on this principle. Plasma phenylalanine can also be determined using this enzyme. Poisner (1960) determined serum phenylalanine levels in schizophrenics using Hsia’s method and obtained a significant elevation over normals.
Unit Definition:1 unit yields 1umole of CO2 per minute from L-tyrosine @ 37°C, pH 5.5.
Activity:≥ 0.1units/mg dw
Optimum pH:5.5
Specificity:Dihydroxyphenylalanine and L-phenylalanine are acted upon at a much slower rate than L-tyrosine.
Stabilizers:Glycerol 10-25%, mercaptoethanol (5mM) and L-tyrosine (0.5mM)
Storage and Stability:Lyophilized powder may be stored at -20°C. Reconstitute to nominal volume, aliquot and store at -20°C. Reconstituted product is stable for 12 months at -20°C. For maximum recovery of product, centrifuge the original vial after thawing and prior to removing the cap.
