Data suggest that rubisco (ribulose-1,5-bisphosphate
carboxylase) makes up 10% of the total protein found in spinach leaves. Research elucidating the structure of rubisco shows that it has 8 active sites. Why, with 8 active sites, might there be such a large concentration of rubisco in plant matter?
Rubisco is a very slow enzyme; what it lacks in speed, it makes up in numbers.