The mol wt of the pine PAL subunit, estimated from the
mobility on SDS-PAGE, is 74,000. The native mol wt of PAL,
estimated by gel filtration chromatography on Sephacryl S-
300, is 280,000, in agreement with the tetrameric nature of
PAL in all organisms examined to date. Flat bed isoelectric
focusing of purified PAL next to a set of standards yielded an
estimate of pl 5.8.
The purified enzyme follows Michaelis-Menten kinetics,
with a Km of 27 ,uM for L-phenylalanine. A double reciprocal
(Lineweaver-Burk) plot shows no sign of an inflection point,
and the Hill coefficient was approximately unity. This observation
contrasts with observations on PAL purified from
many other higher plants. The enzyme is commonly described
as showing negative cooperativity (10).
Purified PAL protein was submitted to N-terminal amino
acid sequence analysis, and 22 amino acids of sequence were
obtained. A degenerate nucleotide sequence that could encode
the observed amino acids was inferred, and an oligonucleotide
primer was synthesized from a portion of the sequence, using
inosine in positions where any of three or four nucleotides
might occur (Fig. 2).