Mac Pro (Mid 2010) variants support 4 x 4 GB or 8 x 4 GB based on the Processor ( Official Spec).
Unofficially it is speculated to work with up to 32GB (4 x 8 GB) and 128 GB (8 x 16 GB) respectively.
Supports DDR3 Unbuffered ECC Memory 1066 MHz and 1333 MHz. Operates at 1.5v. 16 GB sticks may operate at 1.35v.
Note: Based on the processors, the speed at which your MacPro can work will differ. 1600 MHz is not recommended by Apple and may not work for sure.