isoform vs isotype

I'm writing a figure legend. The title is something about P450 inhibitors and in my first version I wrote something like 'bla bla bla cytochrome P450 isoforms'. Now, a co-author argues: wouldn't be better 'cytochrome P450 isotypes'? In fact, isoforms usually refers to different proteins from a same gene, this is not the case for P450s that are coded by different genes, therefore 'isoforms' is improperly used. He is right. However, googling 'P450 isotypes' I get 68,000 results; googling the uncorrect 'P450 isoforms' I get 311,000 of them, including respectful sources. What would have you wrote: isotype or isoform?

Here what I did, I searched cytochromes P450 with Google AdWords Keyword Tool, which gives me an idea of the monthly searches google receives for each term. There are 0 monthly searches for P450 isotypes (right) and just 140 monthly searches for P450 isoforms (wrong), but there are also ~1000 monthly searches for P450 enzymes.

I write down 'bla bla bla cytochrome P450 enzymes'. The term is correct and increases the exposure of my writings to the scientific community.