TABLE 3. Enzymatic properties of OS₂ and its mutants.

The specific activities were measured on [³H]oleate-radiolabeled E.coli membranes and on vesicles composed of the single phospholipid POPG, POPS or POPC using the real-time fluorometric assay employing the fatty acid binding protein. Interfacial binding of sPLA₂ was determined by the centrifugation method on sucrose-loaded vesicles of 20 mole% DOetPS/ 80 mole% DOetPC. The results are representative of at least duplicate experiments with SEM values lower than 40%.

sPLA2	Specific activity				Interfacial binding
	E.coli	POPG	POPS	POPC	DOetPS/PC
	dpm/(pmol × min)	µmol/(min×mg)			Kd (mM) c
venom OS2	1090	433	26	53.7	0.023
rec OS2 WT	1000	471	23	59.1	0.074
OS2 H48Q	2	1.2	0.05	0.05	0.040
OS2 D49K	0a	nd b	nd b	nd b	no binding at 1 mM
OS2 G30S	2.3	0.60	0.03	0.03	no binding at 1 mM
OS2 K31L-R34S	950	169	3.10	61.8	0.007
N-term. chimera	1	2.60	0.003	0.02	no binding at 1 mM
Central chimera	5060	131	5.8	86	0.015
C-term. chimera	1.9	0.01	0.17	0.18	no binding at 1 mM
venom OS1	10	2.40	2.2	9.7	no binding at 1 mM

^aNo sPLA₂ activity is detected at 1 µM after 2 h of incubation.

^bNot determined.

^cThe indicated K_d values are averaged values of K_d values measured by SDS-PAGE analysis (for sPLA₂s with low specific activity), or by both SDS-PAGE and sPLA₂ assays (for sPLA₂s with high specific activity).