Wrong. In a created world, I would assume that unless a particular protein is involved directly in a process that makes one species different from another, i.e. a "furry" protein for cats vs. a "naked" protein for humans, it should have the identical sequence, both at nucleotide and at amino acid levels, and an identical function. From a creationist standpoint, there is absolutely no reason exposure to a certain toxin should be lethal to a guinea pig while a several fold higher dose merely causes a persistant rash in humans. The same protein mediates both responses. The sequence is similar, but not identical in both species. Evolution, not creation, explains the wide variance in response to the toxin.
I am not sure that you can say that the response is due to the same protein. We know far less about biology than we think we know. We do know though that in some cases certain actions and reactions are controlled by more than one gene, by more than one protein. Man probably has another regulator that is affecting this response which the guinea pig does not have. And this you see is one of the problems with evolution. It claims to give an answer to questions when the answer may well lie elsewhere. It said the appendix was just a vestigial organ, it was not, it had a purpose. It said that non-coding DNA was junk, it was not, it had a purpose. We are far from knowing all the answers yet. We do not even know exactly what all the genes are in humans, let alone what the purpose of every one of them is. Our biggest lack though is in the knowledge of the complex interrelationships between cells. We are not even close to an answer on that.