Thank you so much for helping me 
I thought you want me to use the game instance to save the information
The fact is that I want to save information of every object, even unloaded or from another map — exit the game — enter the game again and load the information about objects.
Now if I save the object on first map, I will have the broken(null) reference to the object on the other map. If I save the broken reference - I cannot load the information about this object when I enter the game again.