Granulosa cells produce estrogen with the help of the enzyme :
Alkaline phosphatase
Aromatase
Acid phosphate
Glucuronidase
During the follicular phase under the influence of LH, androgens are produced in the theca cells. The androgens diffuse into granulosa cells where they are aromatised to estradiol androgens-> aromatase -> estradiol and estrone, under FSH influence. Ref: D.C. Dutta's Textbook of Gynaecology, 6th edition, page no: 72
Reproductive physiology and hormones in females