F. Ikegami et al., BIOSYNTHESIS OF BETA-(ISOXAZOLIN-5-ON-2-YL)-L-ALANINE BY CYSTEINE SYNTHASE IN LATHYRUS-SATIVUS, Phytochemistry, 33(1), 1993, pp. 93-98
Two different forms of cysteine synthase (CSase) were purified from th
e grass pea (Lathyrus sativus), being separated by chromatography on D
EAE-Sepharose Fast Flow or EAH-Sepharose 4B. The native isoenzyme A wa
s a dimer with a subunit M(r) of 35 000, whereas the isoenzyme B was a
lso a dimer with a subunit M(r) of 39 000. The K(m) values of isoenzym
es A and B were 6.1 and 7.2 mM for O-acetyl-L-serine (OAS), respective
ly. Data on the substrate specificity show that both isoenzymes cataly
se the formation of beta-(isoxazolin-5-on-2-yl)-L-alanine (BIA), the b
iosynthetic precursor of the neurotoxin beta-N-oxalyl-L-alpha,beta-dia
minopropionic acid (ODAP), and some other heterocyclic beta-substitute
d alanines from OAS as an additional catalytic activity. Antiserum pro
duced from purified spinach CSase isoenzyme A was cross-reactive with
Lathyrus isoenzyme A, but less with isoenzyme B. Several properties, i
ncluding the amino acid compositions of the purified enzymes, and the
intracellular localization of these enzymes in the grass pea and pea (
Pisum sativum) are also described.