Disable a cell based on another cell value

Hello, I'm very new to VB. I have a worksheet with muliple values that get manually input. But with Column D and E they can only enter one or the other. I've been asked to see if I can disable one or the other cells.

Example: If someone entered 25% in Column D cell1 then Column E cell1 would be disabled. This would apply for many rows.

One or the other only for the two below
1 25% disable
2 disable 25%
3 25%

Thanks So much!