[Phenylalanyl-tRNA-synthase from human placenta: isolation and characteristics].

Phenylalanyl-tRNA synthetase (EC 6.1.1.20) from human placenta was isolated and purified using fractionation with polyethyleneglycol and chromatography on hydroxylapatite, heparin-Sepharose and mono-S. The enzyme purified 14800-fold with a 8% yield had a specific activity of 260 U./mg. The molecular mass of the native enzyme as determined by gel filtration was 270 +/- 13 kDa. The molecular masses of the enzyme subunits according to SDS-PAGE data were 74 +/- 4 kDa (alpha-subunit) and 63 +/- 3 (beta-subunit). The Km values for tRNA, ATP and phenylalanine in the aminoacylation reaction were 6.6 X 10(-8) M, 8.3 X 10(-5) M and 5.8 X 10(-6) M, respectively.