Parkinson's disease is characterized by clumps of abnormal brain proteins called Lewy bodies of which a-synuclein (a-syn) protein is the principal component.

WSJ: Exercise Benefits vs. Joint Concerns

Methane is the principal component of natural gas, and massive amounts of it are trapped in reservoirs beneath the sea floor and under a layer of the ice-like substance.

FORBES

In the case of the yen, however, a much larger factor has been so-called Abenomics, whose principal ostensible component is massive quantitative easing.

FORBES: The Dollar Is Flying High -- But How Long Will The Rally Last?

He said that student-achievement data is only one component of the district's teacher-evaluation system, which relies heavily on principal observations.

WSJ: Seattle Teachers Protest Exams