Paul D. Boyer, a molecular biologist who shared the 1997 Nobel Prize in Chemistry for his contributions to understanding the way all organisms get energy from their environments and process it to sustain life and fuel their activities, died on Saturday at his home in Los Angeles. He was 99.

His death was confirmed by his daughter Alexandra Boyer.

A professor emeritus at the University of California, Los Angeles, where he taught chemistry and conducted research for more than 50 years, Dr. Boyer devoted his career to the study of enzymes, those mysterious proteins that power biochemical processes in the cells of plants and animals.

Building on the earlier work of other scientists and his own decades of research, Dr. Boyer deciphered the mechanics of the enzyme that makes ATP (adenosine triphosphate), the link in every cell that acts like a tiny motor, enabling ATP to chemically capture energy from its surroundings and release it as mechanical energy for life to run on.

In a series of 20th-century discoveries, scientists had learned that ATP was the universal carrier of cell energy; that plants and animals created it naturally, although it could be made in a lab; and that the structure of the enzyme ATP synthase consisted of a rotating wheel, an attached axle jutting up from its center and at the top of the axle a fixed cylinder, each carrying its own sets of proteins. ATP is created and released by the interactions of proteins on the wheel, axle and cylinder.