You probably know that a correlation is the relationship between two sets of variables used to describe or predict information. Therefore, the correlation coefficient is the degree in which the change in a set of variables is related.
Delta G is a measure of the net effect of these two concepts, and will help you predict whether or not a reaction will actually take place! Delta G naught refers to the Delta G if you were creating a given compound from its pure elemental form at standard temperature and pressure. So it's how likely a compound would form from its individual elemental components!
This form of NGF is also referred to as proNGF (NGF precursor). The gamma subunit of this complex acts as a serine protease, and cleaves the N-terminal of the beta subunit, thereby activating the protein into functional NGF. The term Nerve Growth Factor usually refers to the 2.5S, 26 kDa beta subunit of the protein.