The biological effects of vanadyl curcumin and vanadyl diacetylcurcumin complexes: the effect on structure, function and oxidative stability of the peroxidase enzyme, antibacterial activity and cytotoxic effect

Figures & data

Figure 1. Circular dichroism spectra of HRP in absence (control) and presence of vanadyl curcumin (VO(cur)₂) and vanadyl diacetylcurcumin (VO (DAC)₃). The molar ratio of HRP to the both curcumin complexes is 1:1.

Figure 2. Intrinsic fluorescence spectra of HRP excited at 280 nm (A) and 295 nm (B) in 0–20 µM concentrations of vanadyl diacetylcurcumin. In the inset figures fluorescence intensity at λ_max has been plotted against molar concentration of the complex.

Figure 3. Intrinsic fluorescence spectra of HRP excited at 280 nm (A) and 295 nm (B) in 0–20 µM concentrations of vanadyl curcumin (B). In the inset figures fluorescence intensity at λ_max has been plotted against molar concentration of the complex.

Figure 4. Percentage of activity of HRP at different concentrations of vanadyl curcumin (VO(cur)₂) and vanadyl diacetylcurcumin (VO(DAC₂). Inset shows the rate of HRP reaction (V) at various concentrations of the complexes.

Figure 5. The rate of reaction of HRP (V) at different concentrations of hydrogen peroxide in absences (0) and presence of 1–3 µM (1, 2 and 3) vanadyl curcumin (A) and vanadyl diacetylcurcumin (B). In the inset figures, the enzyme activity was considered 100% in the absence of the complex.

Figure 6. Percentage of decrease in activity of HRP on the oxidative condition (at 3.12 µM concentration of H₂O₂ that is four-fold more than the optimum concentration of H₂O₂ for the enzymatic assay of HRP) at various concentrations of vanadyl curcumin (VO(cur)₂) and vanadyl diacetylcurcumin (VO(DAC)₂).

Table 1. IC₅₀ values (µM) of hydrogen peroxide in absence (control) and presence of 1, 2 and 3 µM vanadyl curcumin (VO(cur)₂) and vanadyldiacetylcurcumin (VO(DAC)₃).

	VO(cur)2	VO(DAC)2
Control	2.8	3
1 µM	5.2	3.2
2 µM	6.7	4.1
3 µM	6.7	4

Table 2. Michaelis constant for H₂O₂ substrate (¹K_m) and phenol substrate (² K_m), maximum rate of the enzymatic reaction (V_max), catalytic rate constant (k_cat) and catalytic efficiency (k_cat/k_m) of HRP in the absence (control) and presence of 0.5 and 3 µM vanadyl curcumin (VO(cur)₂).

[VO(Cur)2]	^1Km (mM)	^2Km (mM)	Vmax (U/mg)	kcat (s^−1)	kcat/^1Km (s^−1mM^−1)	kcat/^2Km (s^−1mM^−1)
0 µM	0.11 ± 0.01	5.6 ± 0.8	395 ± 23	288 ± 17	2618	51
0.5 µM	0.24 ± 0.03	4.6 ± 0.4	450 ± 57	328 ± 42	1366	71
3 µM	0.36 ± 0.03	3.5 ± 0.5	560 ± 24	408 ± 17	1133	116

Table 3. Michaelis constant for H₂O₂ substrate (¹K_m) and phenol substrate (²K_m), maximum rate of the enzymatic reaction (V_max), catalytic rate constant (k_cat) and catalytic efficiency (k_cat/K_m) of HRP in the absence (control) and presence of 0.5 and 3 µM vanadyl diacetylcurcumin (VO(DAC)₂).

VO(DAC)2	^1Km (mM)	^2Km (mM)	Vmax (U/mg)	kcat (s^−1)	kcat/^1Km (s^−1.mM^−1)	kcat/^2Km (s^−1mM^−1)
0 µM	0.120 ± 0.006	5.15 ± 0.20	386 ± 21	282 ± 15	2350	55
0.5 µM	0.290 ± 0.007	3.80 ± 0.35	501 ± 28	367 ± 20	1262	96
3 µM	0.46 ± 0.02	3.95 ± 0.5	560 ± 14	409 ± 10	889	225

Table 4. Activation energy of the enzymatic reaction (E_a), the free energy of activation (ΔG^#), the enthalpy of activation (ΔH^#) and the entropy of activation (ΔS^#) in the absence (control) and presence of 3 µM vanadylcurcumin (VO(cur)₂) and vanadyldiacetylcurcumin (VO(DAC)₃).

	Ea (kJ mol^−1)	ΔG^# (kJ mol^−1)	ΔH^# (kJ mol^−1)	ΔS^# (kJ mol^−1 K^−1)
Control	57.1 ± 2.1	54.6 ± 2.1	54.6 ± 2.1	0.17 ± 0.02
VO(Cur)2	39.9 ± 1.2	37.3 ± 1.1	37.4 ± 1.2	0.13 ± 0.001
VO(DAC)2	51.6 ± 1.6	49.1 ± 1.6	49.1 ± 1.7	0.15 ± 0.02

Figure 7. Viability of MCF-7 (C135) breast cancer, bladder (C5637) and LNCaP (C439) prostate carcinoma cell lines at various concentrations of vanadyl curcumin (VO(cur)₂) assayed by MTT method.

Figure 8. Viability of MCF-7 (C135) breast cancer, bladder (C5637) and LNCaP (C439) prostate carcinoma cell lines at various concentrations of vanadyl diacetylcurcumin (VO(DAC)₂) assayed by MTT method.