So you found it in sap, spro transaction.
If you read the help and follow the link on changing the Standard derivation rules (from menu view- display all steps) then you will find the rules for profit center. You will see more than one, and this is because different rules may work for different sources.
What you can see in each rule is from which table/record is coming the profit center. The simple way is take an example from PA database and check which rule applies in your case.
You can find also in the PA record from which table is reading the derivation rule the data.
If you don't have so much experience with it, i suggest you ask for help from an FI-CO consultant.
Thank you
Yiannis