Question

The most abundant protein is
A. Rubisco
B. Haemoglobin
C. Ferredoxin
D. Cytochrome

Answer 1

Hint: The most abundant protein in the world is present in every plant that performs photosynthesis. It is used in the Calvin cycle of photosynthesis to catalyze the first major step of carbon fixation.

Complete answer:
The enzyme Ribulose-1, 5 bisphosphate carboxylase oxygenase, is commonly known as Rubisco and it makes about 20-25% of the soluble protein in the leaves.
This enzyme can bind to both carbon dioxide and oxygen on its active sites but it has a much greater affinity for carbon dioxide than oxygen. This binding is competitive. When carbon dioxide concentration is low and the temperature is high, it acts as an oxygenase. Otherwise, it behaves as a carboxylase.
Carboxylation is the most crucial step of the Calvin cycle in which carbon dioxide is utilized for the carboxylation of RuBP carboxylase which results in the formation of two molecules of 3-PGA.
Conversion of RuBP into oxygenase occurs in the photorespiration. In plants, RuBisCo binds to oxygen and its carbon dioxide fixation is decreased. Here the RuBP instead of being converted to PGA, bids to oxygen and forms phosphor glycolate.
Haemoglobin
It is the red colored pigment in the blood of all vertebrates and its function is to carry oxygen through the blood to the various parts of the body.
Ferredoxin
It is a small protein that contains iron and sulfur atoms organized as iron-sulfur clusters. It acts as an electron acceptor and is associated with the photosystem-I in photosynthesis.
Cytochrome
Cytochrome is a protein associated with redox catalysis and electron transport chain. They have a central Fe atom and heme as a cofactor.

Note: Rubisco is present on the outer surface of the thylakoid membrane of the chloroplast.. This enzyme was isolated as fraction 1 protein and later called as carboxy dismutase.