Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Chemistry of Conjugated Proteins
Chromoproteins

As noted earlier, Conjugated Proteins consist of two components: a simple protein and a non-protein substance. The latter is referred to as a prosthetic group (from the Greek prostheto meaning 'to attach'). As a rule, prosthetic groups are tightly bound to the protein molecule. Below is An Overview of the chemical nature and biological roles of certain conjugated proteins.

Chromoproteins (from the Greek chroma meaning 'color') are composed of a simple protein and a colored non-protein component bound to it. They are classified into Hemoproteins (containing iron within the prosthetic group), magnesium Porphyrins, and flavoproteins (containing isoalloxazine derivatives). Chromoproteins perform a wide array of unique biological Functions: they are involved in fundamental life processes such as Photosynthesis, cellular and systemic Respiration, oxygen and Carbon dioxide transport, oxidation-reduction reactions, as well as light and color perception, among others.

Thus, chromoproteins play an exceptionally vital role in life processes. For instance, the suppression of Hemoglobin's respiratory function through the administration of carbon monoxide (CO), or the inhibition of cellular oxygen uptake in Tissues via hydrocyanic acid or its salts (cyanides)—which block cellular respiration enzyme systems—leads to instant death of the Organism.

Chromoproteins are essential and active participants in energy accumulation, ranging from the fixation of solar energy in green plants and its utilization to various transformations within animal and human bodies. Chlorophyll (a magnesium porphyrin), together with a protein, drives photosynthetic activity in plants by catalyzing the splitting of Water molecules into hydrogen and oxygen (via the absorption of solar energy). Conversely, hemoproteins (iron porphyrins) catalyze the reverse reaction—The formation of water molecules coupled with the release of energy.