ferredoksiinin

Ferredoksins are a group of small, iron-sulfur proteins that act as electron carriers in a wide variety of metabolic processes. They are found in almost all organisms, from bacteria and archaea to plants and animals. The defining characteristic of ferredoxins is the presence of one or more iron-sulfur clusters, which are prosthetic groups consisting of iron atoms and inorganic sulfide ions coordinated by cysteine residues of the protein. These iron-sulfur clusters are responsible for the redox activity of ferredoxins, enabling them to readily accept and donate electrons.

The structure of ferredoxins varies depending on the number and type of iron-sulfur clusters they contain. Common types include [2Fe-2S], [3Fe-4S], and [4Fe-4S] clusters. The precise arrangement of iron and sulfur atoms within these clusters dictates their redox potential, allowing them to participate in electron transfer reactions at specific energy levels. This specificity is crucial for their diverse roles in biological systems.

In photosynthesis, ferredoxins play a vital role in the light-dependent reactions of plants and algae. They transfer electrons from photosystem I to NADPH reductase, a key enzyme in the production of the reducing agent NADPH, which is essential for carbon fixation in the Calvin cycle. In many bacteria and archaea, ferredoxins are involved in a similar electron transport chain. Beyond photosynthesis, ferredoxins are implicated in a multitude of other metabolic pathways, including nitrogen fixation, steroid metabolism, and the detoxification of xenobiotics. Their ability to mediate single-electron transfers makes them indispensable components of numerous biological redox reactions.