Global disable pull-up resistors Arduino Mega

Hi i was wondering how to global disable pull up resistors on the arduino mega 1280. I've tried _SFR_IO8(0x35) |= 0x10; but it seems not to work any suggestions on how to get it working?

Does this work…

MCUCR |= ( 1 << PUD );

Well its done something but its not behaving the way i was expecting so cant say if its really working or not, there may be a bug in my code.