Catalase A from Saccharomyces cerevisiae and its biosynthetic precursors can specifically be
immunoprecipitated from extracts obtained from yeast cells grown in the presence of L- [3H]leucine
or 59FeCls. The enzyme and its precursors recognized by a specific antiserum are absent from
anaerobic cells. During oxygen adaptation of yeast pre-grown on 0.3 % glucose under anaerobic
conditions catalase A is formed via a heme-less precursor, probably the apomonomer of the protein,
and a heme-containing intermediate. When cells are grown in the presence of Tween 80 the amount
of catalase A, but not of catalase T, increases 4-fold. Comparison of the mode of synthesis of
catalase T and A shows that no precursor-product relationship exists between the two proteins.