Pyridoxal 5' phosphate involvement in age-related modifications of tyrosine aminotransferase: multiple form patterns.

Multiple form patterns of tyrosine aminotransferase were studied in senescent and adult rat liver. Two main modifications were described for "old" rat enzyme: (i) appearance of a new molecular form, specific for old rats, eluted after adult form III and having other properties identical to this form; (ii) disappearance of intermediate forms II and III after enzyme induction; this result seems to be due to acceleration of the conversion process. Vitamin B6 deficiency of old rats explain this and other (previously described) post-translational modifications of "old" tyrosine aminotransferase. The influence of pyridoxal 5' phosphate and the role of protease(s) in the multiple form conversion are discussed. Moreover we show the possibility of a correlation between in vivo alterations of the enzyme molecule and modifications of tyrosine aminotransferase multiple form patterns observed in vitro.