Multiple choice Most abundant protein in the world is _________. albumin collagen osteocalcin RuBisCO keratin Reveal answer Fill a bubble to check yourself D Correct answer Explanation RuBisCO (Ribulose-1, 5-bisphosphate carboxylase) is thought to be the most abundant protein in the world, since it is present in every plant that undergoes photosynthesis and molecular synthesis through Calvin cycle.