Table 1.
Menadione Effect on Activities of Key Mitochondrial and Cytosolic-Oxidized Nicotinamide Adenine Dinucleotide-Linked and Oxidized Nicotinamide Adenine Dinucleotide Phosphate-Linked Dehydrogenases Under Various Glucose Concentrations
| |
18.3 mM glucose + MQ (μM) |
6.1 mM glucose + MQ (μM) |
1.2 mM glucose + MQ (μM) |
||||||
|---|---|---|---|---|---|---|---|---|---|
| Cellular enzymes | 0 | 50 | 200 | 0 | 50 | 200 | 0 | 50 | 200 |
| cyto NADK (U/min/mg prot) |
1.1 ± 0.07 | 1.36a ± 0.08 | 1.29a ± 0.05 | 0.98 ± 0.05 | 1.67b ± 0.1 | 1.76b ± 0.08 | 0.46c ± 0.05 | 0.56 ± 0.06 | 0.82b ± 0.05 |
| cyto ICDH-NADP+ (nmol/min/mg prot) |
78.55 ± 3.8 | 76.9 ± 2.9 | 71.1 ± 3 | 82.88 ± 6.8 | 82.75 ± 3.9 | 75.57 ± 5 | 54.53c ± 3 | 58.9c ± 2.8 | 65.1 ± 4.3 |
| cyto ME-NADP+ (nmol/min/mg prot) |
26.87 ± 2.9 | 30.2 ± 2.9 | 26.8 ± 3 | 28.88 ± 2.3 | 36.8a ± 1.7 | 36.27a ± 3.1 | 23.9 ± 2.2 | 27.9 ± 4 | 36.5 ± 8.8 |
| cyto G6PDH (nmol/min/mg prot) |
58.2 ± 5.5 | 74.7 ± 20.9 | 66.6 ± 22.1 | 55.79 ± 4.6 | 62.2 ± 3.7 | 53.01 ± 3 | 39.16 ± 2 | 44.6 ± 3.7 | 55.5a ± 7.7 |
| mito ICDH-NAD+ (nmol/min/mg prot) |
326.3 ± 24.6 | 308.8 ± 13.9 | 305.9 ± 14.8 | 297.1 ± 25.9 | 358.3a ± 14.2 | 341.9a ± 19 | 359 ± 43 | 423 ± 123 | 441 ± 135 |
| mito NNT (nmol/min/mg prot) |
5.8 ± 0.4 | 8.8 ± 2.0 | 14.1 ± 4.4 | nd | nd | nd | 6.7 ± 0.7 | 11.5 ± 2.5 | 21.8a ± 3.6 |
| mito ICDH-NADP+ (nmol/min/mg prot) |
280.9 ± 22.2 | 271.61 ± 14.9 | 251.7 ± 13.6 | 263.03 ± 12 | 310.9 ± 20 | 268.3 ± 18.8 | 285.5 ± 15 | 316.7 ± 18 | 267.1 ± 58 |
Cell incubations with MQ under different glucose conditions, preparation of cell lysates, and enzyme assays were as described in Methods. With the exception of NADK and NNT, all enzyme activities are expressed as the amount of NADPH or NADH produced per minute per milligram protein. NADK activity is expressed in Units; one Unit is the amount of enzyme generating 1 μmol of NADP+ in 1 min at 30°C. NNT activity is expressed as nmol of 3-acetylpyridine adenine nucleotide reduced per minute per milligram protein. Results are mean ± standard error of the mean for six separate cell preparations for all enzymes and three preparations for NNT.
p < 0.05.
p < 0.001 are statistically different from untreated controls at each glucose concentration.
p < 0.05 at 0.2 g/l glucose are statistically different from 3 g/l glucose.
MQ, menadione; NADK, NAD kinase; ICDH, isocitrate dehydrogenase; ME, malic enzyme; G6PDH, glucose 6-phosphate dehydrogenase; NNT, nicotinamide nucleotide transhydrogenase; cyto, cytosolic; mito, mitochondrial; nd, not determined.