Openly gay philanthropist Jon Stryker has given $325,000 to fight a proposed constitutional amendment which would ban gay marriage in Minnesota.

Stryker of Kalamazoo, Michigan gave the gift to Freedom to Marry Minnesota's political action committee on Tuesday, the AP reported.

Minnesota United for All Families, the coalition of groups working to defeat the November referendum, was formed by Freedom to Marry.

Stryker and sisters Pat and Ronda are heirs to the Stryker Corporation medical supply company fortunes of grandfather Homer Stryker. Jon Stryker founded the Arcus Foundation to further his social and environmental activism.

In 2008, Stryker told The Chronicle of Philanthropy that he prefers to stay out of the spotlight. He has donated hundreds of millions of dollars to support gay rights causes and great-ape conservation. He has also spent millions of his fortune to elect lawmakers who support causes he cares about.

“I'm probably one of the wealthiest gay men in this country, and I felt I had a big responsibility,” Stryker said about assuming a role in advancing human rights. “I'd never been involved with civil-rights work so directly before, and I just felt it was a calling. There were very few individuals involved, and I felt I could have a big impact.”