four sequential steps. Dialysed S35 extracts were mixed slowly with
0.1 vol. 1 % (w/v) protamine sulphate (Sigma) in TM buffer with gentle
agitation for 20 min. The nucleic acid precipitate was removed by
centrifugation at 15000g for 20 rnin and the supernatant was
chromatographed through a DEAE-Sephacel (Pharmacia) anion
exchange column equilibrated with TM buffer. The column was
washed with 200 ml of TM buffer and the proteins eluted with 200 ml of
a linear gradient (0-0.5 M) of ammonium sulphate in TM buffer. The
active fractions were collected, pooled and fractionated with increasing
concentrations of ammonium sulphate (Sigma; enzyme grade). Most of
the L-asparaginase activity precipitated in the 30-45 % saturation
fraction. The enzyme precipitate was dissolved in TM buffer and
filtered through a Sephacryl S-200 or Sephadex G-200 column
(2.6 x 100 cm), eluting with TM buffer at a flow rate of 0.5 ml min-l.
The M, of L-asparaginase was calculated by comparison with globular
proteins of known M, (Pharmacia calibration kit). Partially purified
preparations kept their activity when frozen at - 80 "C but lost 50% of
their activity in 5 d at 4 "C.