Implying activity of other genes

[abfmdf]

I have characterised the activity of a new enzyme and as the genome has been sequenced I have been looking at the surrounding genes.

Now the surrounding genes are all interrelated in a degradation pathway ie

Gene 1 (predicted to act on known substrate) converts A to B
Gene 2 (predicted to act on known substrate) converts B to C
Gene 3 (my enzymes) I know from experiments converts C to D
Gene 4 (enzyme type predicted, but not substrate it acts on) (D to E)
Gene 5 (predicted to act on substrate) to convert E to F

Is it scientifically correct to infer the substrate specificity (ie gene 4 acts on D) given the interrelationship of the other predicted genes and from what I know about my enzyme?

The results of a blast search of gene 4 shows mainly the broad enzyme type (ie aldehyde dehydrogenase), although there is one high hit E=0 that is predicted to be a specific enzyme which acts on the product (aldehyde) of my enzyme.

As I know my enzyme is upregulated when I add C and I know the products of my enzyme, am I able to imply that this degradation pathway (that occurs in 1 other bacteria) also occurs in my bacteria? Or is proof required by scientific experiments?