Induction of tyrosine alpha-ketoglutarate transaminase by steroid hormones in a newly established tissue culture cell line.

Abstract

Tyrosine [alpha]-ketoglutarate transaminase can be induced by steroid hormones in a newly established line of tissue culture cells, derived from primary culture of the ascites form of an experimental rat hepatoma. The isolation, growth, and morphology of the tissue culture cells are described. Heat inactivation studies and disc gel electrophoresis suggest that induced and basal tyrosine transaminase are the same. The enzyme activity is stabilized to heat by pyridoxal phosphate or [alpha]-ketoglutarate, but made unstable to heat by pyridoxal. Kinetics of tyrosine transaminase induction reveal a 2-hr, lag after addition of steroid, followed by a rapid rise in enzyme for 5-8 hr. to a plateau level about 10 times the basal activity. The induced level is maintained as long as steroid is present. The induction is blocked by puromycin, cycloheximide, chloramphenicol, progesterone, actinomycin D, and mitomycin C. After induction by steroid has taken place, actinomycin D produces a further increase in enzyme activity.