Abstract: A composition is provided, comprising purified alkaline gland fluid (AGF) from the alkaline gland of a cartilaginous fish. The invention also provides a purified protein of approximately 12 kD as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis under non-denaturing conditions, that decreases sperm motility and can be purified from the alkaline gland of a cartilaginous fish. Further provided are purified proteins that increase sperm motility and can be purified from the alkaline gland of a cartilaginous fish. Particularly, purified proteins of approximately 160 kD, approximately 32 kD and approximately 18 kD as determined by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) under non-denaturing conditions increase sperm motility. A method of increasing sperm motility comprising the step of contacting sperm with an amount of the present purified AGF composition or purified proteins effective to increase the motility of the sperm is also provided.