Method
Reagents
| A. Tris-HCl buffer, pH 7.8 | 55 mM (containing 3.3 mM magnesium chloride) |
|---|
| B. NAD+ solution | 60 mM (Should be prepared fresh) |
|---|
| C. G-6-P solution | 0.1 M glucose-6-phosphate (should be prepared fresh) |
|---|
| D. Enzyme diluent | 5 mM Tris-HCl buffer, pH 7.5, containing 0.1 % of bovine serum albumin. |
|---|
Procedure
1.Prepare the following reaction mixture in a cuvette (d = 1.0 cm) and equilibrate at 30 ℃ for about 5 minutes.
| 2.7 mL | Tris-HCl buffer, pH 7.8 | (A) |
| 0.1 mL | NAD+ solution | (B) |
| 0.1 mL | G・6・P solution | (C) |
| Concentration in assay mixture |
|---|
| Tris-HCl buffer | 50 mM |
|---|
| G-6-P | 3.3 mM |
|---|
| NAD+ | 2.0 mM |
|---|
| MgCl2 | 3.0 mM |
|---|
| BSA | 33 μg/mL |
|---|
2.Add 0.1 mL of the enzyme solution* and mix by gentle inversion.
3.Record the increase in optical density at 340 nm against water for 4 to 5 minutes with a spectrophotometer thermostated at 30 ℃ and calculate the ΔOD per minute from the initial linear portion of the curve (ΔOD test).
At the same time, measure the blank rate (ΔOD blank) using the same method as the test except that the enzyme diluent is added instead of the enzyme solution.
*Dissolve the enzyme preparation in ice-cold enzyme diluent (D) and dilute to 0.05−0.20 U/mL with the same buffer, immediately before the assay.
Calculation
Activity can be calculated by using the following formula :
Weight activity (U/mg) = (U/mL)×1/C
| Vt | : Total volume (3.0 mL) |
| Vs | : Sample volume (0.1 mL) |
| 6.22 | : Millimolar extinction coefficient of NADH (cm2/micromole) |
| 1.0 | : Light path length (cm) |
| df | : Dilution facter |
| C | : Enzyme concentration in dissolution (c mg/mL) |
REFERENCES
1)A.Ishaque,M.Mihausen and H.R.Levy; Biochem. Biophys. Res. Comm., 59, 894 (1974).
2)C. Olive, M.E. Geroch and H.R.Levy; J.Biol.Chem., 246, 2043 (1971).
3)M.Milhausen and H.R. Levy; Eur.J.Biochem., 50, 453 (1975).
4)E.L.Coe and L.-H.Hsu; Biochem. Biophys. Res. Comm., 53, 66 (1973).
5)C.Olive and H.R. Levy; Biochem., 6, 730 (1967).
6)R.P.Metzger, S.A. Metzger and R.L. Parsons; Arch Biochem. Biophys., 149, 102 (1972).
7)Methods in Enzymology, Vol, 1, p328 (S.P.Colowick and N.O.Kapalan,eds.), Academic Press, New York (1955).
Table 1. Effect of Various Chemicals on Glucose-6-phosphate dehydrogenase
[The enzyme dissolved in 50 mM Tris-HCl buffer,pH 7.5 (5.25 U/mL) was incubated with each chemcal for 1 hr at 30 ℃.]
| Chemical | Concn.(mM) | Residual
activity(%) |
|---|
| None | – | 100 |
|---|
| Metal salt | 2.0 | |
| AgNO3 | | 86 |
| Ba(OAc)2 | | 51 |
| CaCl2 | | 90 |
| Cd(OAc)2 | | 74 |
| CoCl2 | | 80 |
| CuSO4 | | 66 |
| FeCl3 | | 0 |
| FeSO4 | | 1 |
| HgCl2 | | 84 |
| MgCl2 | | 90 |
| MnCl2 | | 89 |
| NiCl2 | | 89 |
| Pb(OAc)2 | | 3 |
| Zn(OAc)2 | | 67 |
| ZnSO4 | | 53 |
| KF | 2.0 | 93 |
| NaF | 20.0 | 98 |
| NaN3 | 20.0 | 93 |
| Chemical | Concn.(mM) | Residual
activity(%) |
|---|
| NEM | 2.0 | 91 |
| PCMB | 2.0 | 96 |
| MIA | 2.0 | 14 |
| Iodoacetamide | 2.0 | 0 |
| EDTA | 5.0 | 94 |
| (NH4)2SO4 | 20.0 | 98 |
| Borate | 20.0 | 95 |
| o-Phenanthroline | 2.0 | 93 |
| α,α′-Dipyridyl | 2.0 | 95 |
| Urea | 2.0 | 93 |
| Guanidine | 2.0 | 93 |
| Hydroxylamine | 2.0 | 91 |
| Na-cholate | 1.0 % | 102 |
| Triton X-100 | 1.0 % | 100 |
| Brij 35 | 1.0 % | 4 |
| SDS | 0.1 % | 0 |
| Tween 20 | 0.1 % | 101 |
| Span 20 | 0.1 % | 99 |
| DAC | 0.1 % | 0 |
Ac, CH3CO; NEM, N-Ethylmaleimide; PCMB, p-Chloromercuribenzoate; MIA, Monoiodoacetate; EDTA, Ethylenediaminetetraacetate; SDS, Sodium dodecyl sulfate; DAC, Dimethylbenzylalkylammoniumchloride.

Fig.1. Stability (Powder form)
(kept under dry conditions)

Fig.2. Stability (Powder form)
(kept under dry conditions)

Fig.3. Stability (Liquid form at 5 ℃)
enzyme concentration:5,000 U/mL composition:3.2 M ammonium sulfate,pH 6.0

Fig.4. pH-Activity
30 ℃ in the following buffer solution: pH 5.7-6.8, 15 mM Veronal-CH3COONaHCI;pH 6.8-8.5,50 mM Tris-HCI; pH 8.5-9.5, 50 mM glycine-NaOH

Fig.5. Temperature activity
(in 50 mM Tris-HCI buffer, pH 7.8)

Fig.6. pH-Stability
30 ℃, 17 hr-treatment with the following buffer solution: pH 5.0-7.8, 30 mM VeronalCH3COONa-HCI;pH 7.5-8.5, 0.1 M Tris-HCI; pH 8.5-9.5,0.1 M glycine-NaOH

Fig.7. Thermal stability
30 min-treatment with 5.0 mM glycineNaOH buffer, pH 8.0, containing 0.1 % of bovine serum albumin
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