Table 2.
Overview of electron donor specificity of MtLPMO9A, MtLPMO9B or MtLPMO9C
| Group | No. | Reducing agent | MtLPMO9A | MtLPMO9B | MtLPMO9C | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Activity compared to ascorbic acid % | ||||||||||||
| C1-/C4-ox and non-ox | C1-ox | C4-ox | Non-ox | C1-/C4-ox and non-ox | C1-ox | Non-ox | C1-/C4-ox and non-ox | C4-ox | Non-ox | |||
| I | 1 | 3-Hydroxy-4-methoxycinnamic acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 |
| 2 | Homovanillic acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 3 | Naringin | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 4 | p-coumaric acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 5 | Sinapic acid | 23 | 23 | 31 | 24 | 4 | 3 | 14 | 15 | 12 | 18 | |
| 6 | Syringic acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 7 | Vanillic acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| II | 8 | (−)-Epicatechin | 77 | 68 | 90 | 27 | 21 | 19 | 34 | 21 | 15 | 26 |
| 9 | (+)-Catechin | 43 | 47 | 41 | 24 | 7 | 6 | 17 | 6 | 5 | 7 | |
| 10 | 3,4-Dihydroxybenzaldehyde | 9 | 13 | 7 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 11 | 3,4-Dihydroxybenzoic acid | 13 | 15 | 13 | 0 | 1 | 1 | 2 | 4 | 5 | 3 | |
| 12 | 3,4-Dihydroxycinnamic acid | 0 | 0 | 0 | 0 | 49 | 48 | 63 | 0 | 0 | 0 | |
| 13 | 3,4-Dihydroxyphenylacetic acid | 92 | 79 | 105 | 68 | 18 | 17 | 31 | 12 | 9 | 14 | |
| 14 | 3-Methylcatechol | 102 | 87 | 121 | 49 | 22 | 20 | 38 | 14 | 15 | 12 | |
| 15 | 4-Chlorocatechol | 72 | 68 | 75 | 74 | 8 | 7 | 24 | 24 | 21 | 26 | |
| 16 | Caffeic acid | 49 | 49 | 52 | 20 | 8 | 7 | 26 | 0 | 0 | 0 | |
| 17 | Carminic acid | 8 | 7 | 8 | 21 | 0 | 0 | 0 | 3 | 2 | 4 | |
| 18 | Catechol | 65 | 57 | 75 | 26 | 8 | 7 | 18 | 11 | 12 | 10 | |
| 19 | Chlorogenic acid | 36 | 38 | 36 | 25 | 4 | 3 | 18 | 0 | 0 | 0 | |
| 20 | Dopamine hydrochloride | 93 | 71 | 105 | 132 | 46 | 45 | 57 | 6 | 2 | 10 | |
| 21 | l -3,4-Dihydroxyphenylalanine | 101 | 75 | 123 | 86 | 79 | 78 | 84 | 33 | 26 | 41 | |
| 22 | Quercetin | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 23 | Taxifolin | 0 | 0 | 0 | 0 | 15 | 15 | 20 | 4 | 3 | 4 | |
| 24 | Resorcinol | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 25 | Hydroquinone | 51 | 55 | 51 | 25 | 2 | 1 | 10 | 5 | 4 | 7 | |
| III | 26 | Gallic acid | 81 | 72 | 94 | 38 | 46 | 45 | 54 | 22 | 18 | 26 |
| 27 | (−)-Epigallocatechin-gallate | 76 | 56 | 97 | 30 | 79 | 79 | 83 | 11 | 9 | 12 | |
| 28 | Tannic acid | 0 | 0 | 0 | 0 | 18 | 13 | 66 | 0 | 0 | 0 | |
| IV | 29 | Reduced glutathione | 0 | 0 | 0 | 0 | 16 | 15 | 30 | 8 | 7 | 8 |
| 30 | l -cysteine | 16 | 23 | 13 | 0 | 22 | 20 | 40 | 6 | 7 | 4 | |
| 31 | Allyl iso-thiocyanate | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| 32 | d-methionine | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
| V | 33 | Ascorbic acid | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 | 100 |
| Peak area (nC x min)a | (0.897) | (0.460) | (0.058) | (0.360) | (3.273) | (2.962) | (0.311) | (1.542) | (0.760) | (0.781) | ||
| 34 | d-quinic acid | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | 0 | |
The total sum of integrated peak areas of released oxidized (C1-ox, C4-ox) and non-oxidized (non-ox) and both (ox and non-ox) gluco-oligosaccharides from RAC, incubated with either MtLPMO9A, MtLPMO9B or MtLPMO9C in the presence of ascorbic acid, was taken as a reference and equals to 100 % of the LPMO activity. The numbers correspond to the relative activity of MtLPMO9A, MtLPMO9B or MtLPMO9C compared to ascorbic acid (total sum integrated peak areas of released oxidized and non-oxidized gluco-oligosaccharides of a reducing agent compared to ascorbic acid (areas from Fig. 5). Auto-oxidation of RAC was absent for all reducing agents tested based on the absence of oxidized or non-oxidized gluco-oligosaccharides. Reducing agents that can donate electrons to all three LPMOs are highlighted in italics. See “Methods” for details about the activity assays
aIntegrated peak areas of released C1-, C4-oxidized and non-oxidized gluco-oligosaccharides after incubation of MtLPMO9A, MtLPMO9B and MtLPMO9C with RAC in the presence of 1 mM ascorbic acid based on HPAEC (Fig. 5)