TheFallenMadonna
Here's the first page of the search you said you did (not sure why you chose the word 'enzyme')
First result: "The effects of gender, age, ethnicity, and liver cirrhosis on cytochrome P450 enzyme activity in human liver microsomes and inducibility in cultured human hepatocytes"
A Parkinson, DR Mudra, C Johnson, A Dwyer… - Toxicology and applied Pharmacology, 2004
For contrast, here are the results for the phrase 'sex chromosomes'
First result (out of 119,000): "Sex chromosomes and brain gender"
AP Arnold - Nature Reviews Neuroscience, 2004
And here are the results for the phrase "gender chromosomes".
There are only 119 results. Things like this:
"Changing sex: Transsexualism, technology, and the idea of gender"
BL Hausman - 1995 - books.google.com
"Gender: An ethnomethodological approach"
SJ Kessler, W McKenna - 1985 - books.google.com
Gender and sex are not used interchangeably in science.