Table 1. Effects of various substrates and reagents on SOR activity.

The substrate (sulphur) concentration was 78 mM.

			Activity (%)
Substrate	Reagent	Reagent concentration (mM)	Oxygenase	Reductase
Sulphur (S8)	–	–	100	100
	EDTA	1	127	143
	EDTA	10	150	141
	EDTA	50	160	108*
	EDTA	100	134	13*
	Ca2+	1	82	101
	Mg2+	1	110	92
	Sodium citrate	1	103	85
Sulphur (S8), EDTA-washed	–	–	104	94
	EDTA	10	147	124
	Zn2+	0.5	5	16
	EDTA/Zn2+	1/0.5	114	86
	Fe(III) citrate	0.1	102	19*
	Fe(III) citrate	0.01	96	1*
	(NH4)2Fe(SO4)2	0.1	105	150
	(NH4)2Fe(SO4)2	0.01	110	90
No sulphur	K2 Tetrathionate	10	0	0

* Interference with the colorimetric assays.