Comparison of Polyphenol Oxidases Prepared From Different Parts of Artichoke (Cynara Scolymus L.)

Figures & data

Table 1 Substrate specificity of artichoke PPO

	U mL min^−1	U mL min^−1
Substrate	Head	Leaf + Stem
Catechol	8820	3370
Pyrogallol	1670	1270
L-DOPA	2250	600

Table 2 K _m and V _max values of artichoke head and artichoke leaves-and-stem PPO

	Km (mM)		V max (U mLmin^−1)		V max/Km
Substrate	ahPPO	alSPPO	ahPPO	alSPPO	ahPPO	alSPPO
Catechol	7.7	5.4	16,666	16,667	13,964	18,481
Pyrogallol	1.7	2.7	714	1316	2709	2918
L-DOPA	2.1	8	1111	2857	3413	2138

Table 3 The I₅₀ values of different inhibitors for both artichoke PPOs

	I50 (mM)
Inhibitor	Leaf + Stem	Head
L-cysteine	0.097	0.079
Sodium azide	3.67	3.19
Na-EDTA	23.4	11.8
Potassium cyanide	0.022	0.016
Citric acid	41.3	25.5
Ascorbic acid	0.09	0.08
Benzoic acid	3.9	4.5
Thiourea	0.12	0.1
β-mercaptoethanol	0.18	0.1
Sodium bisulphite	0.105	0.109
Ethylene glycol	7.6	5.6
Thioacetamid	0.14	0.15

Figure 1 Effect of pH on _ALSPPO activity (A) and _AHPPO activity (B).

Figure 2 Effect of temperature on _ALSPPO activity (A) and _AHPPO activity (B)

Figure 3 Effect of temperature on stability of _ALSPPO activity (A) and _AHPPO activity (B). The enzyme solution was incubated for various time intervals (5–60 min) at the specified temperature (40–80°C) and rapidly cooled. The activity was measured at 25°C, was taken as 100% and activities measured (40–80°C) were compared with the activity measured at 25°C.

Figure 4 T_m (midpoint of thermal inactivation) for both artichoke PPOs

Table 4 The effect of different activators on catecholase activity for both artichoke PPOs

	Relative activity (%)
Activator	Leaves-and-stem	Head
None	100	100
SDS
(1 mM)	106	130
(10 mM)	106	132
Urea
(1 mM)	102	111
(10 mM)	108	120
CuSO4
(1 mM)	139	127
(2 mM)	146	141