Title: Costs and Consequences of Cellular Compartmentalization and Substrate Competition among Human Enzymes Involved in Androgen and Estrogen Synthesis Short title: Partitioning and substrate competition in steroidogenesis Summary sentence: Compartmental expression of steroidogenic enzymes limits sex steroid synthesis in reproductive tissues, and minimizing flux through the delta-4 pathway by lowering or inhibiting 3beta-hydrogysteroid dehydrogenase expression or activity can (paradoxically) increase androgen synthesis