Two questions
1. Significance 
2. Lack of consistency between enzymes (log2) within the arginine and proline metabolism pathway.

.  1. We've dealt with significance in a past post on Limma (it was not voom though). I'll try and find the post and link it here.

2. The answer is straight forward: whilst all four enzymes include Arginine and proline metabolism pathway 

* only ARG and ODC1 share exactly the same pathways. Thus these should give very similar results. 

* NOS1 is a key enzyme in 6 different pathways.
 
* ALDH2 is involved in 13 different pathways. 

Therefore NOS1 and ALDH2 would have "confounders" (from an experimental perspective, not host metabolism) because they are more complex than singly arginine and proline metabolism pathways.

The other factor is in cancer patients the transcriptomics will get messed up, ALDH2 could go all over the place.

*Prediction*  ARG = ORD < NOS1 < ALDH2

```
**ALDH2** aldehyde dehydrogenase 2 
Pathways
Glycolysis / Gluconeogenesis
Ascorbate and aldarate metabolism
Fatty acid degradation
Valine, leucine and isoleucine degradation
Lysine degradation
**Arginine and proline metabolism**
Histidine metabolism
Tryptophan metabolism
beta-Alanine metabolism
Glycerolipid metabolism
Pyruvate metabolism
Pantothenate and CoA biosynthesis
```

```
**ARG** arginase
Pathways
**Arginine and proline metabolism**
Glutathione metabolism
```
```
**NOS1** nitric oxide synthase 
Pathways
Arginine biosynthesis
**Arginine and proline metabolism**
Calcium signaling pathway
Phagosome
Apelin signaling pathway
```
```
**ODC1** ornithine decarboxylase 1
Pathways
**Arginine and proline metabolism**
Glutathione metabolism
```