Golden apple of Baba Yaga

This apple was given by Baba Yaga to Sasha after she asked her for goodberries, which apparently did not grow in the Otherworld in the winter. Its exact purpose is unknown, though based on what she said, it must have curative properties. The crone told Sasha not to eat the whole fruit at once.
Subsequently, Sasha gave the apple to Sergei Reznikov in Krinets, so that he could question his contacts and find out its price. However, the princeling took the apple and left town with it. Sasha fears that he wants to plant the seeds to produce more apples.
Physically, it appears as a normal apple with a golden sheen that shines dimly in darkness.
The items is still presumably in Reznikov's possession.