## 1 Introduction  
Ferredoxins are proteinaceous electron carriers that play key physiological roles ensuring an electron flux to many essential biochemical pathways [1; 2], such as--among others--steroid hormones biosynthesis in the adrenal mitochondria of vertebrates [3]. They shuttle electrons through the binding of various iron-sulfur clusters, mainly [3F4S] or [4F4S]. Other types of clusters are [3F4S] together with one [4F4S], and two [4F4S][4; 5; 6; 7]. Adrenodoxin is also a member of the ferredoxin family, binding the simplest polymetallic system, [2F2S] Fd, distributed in three classes: plant type, bacterial type and vertebrate type, with a structure in the core very similar [3]. Bovine adrenodoxin, for instance, is part of the mitochondrial electron transport chain responsible for the production of steroid hormones in mammals [8]. Electron transport among ferredoxins is realized by a change in the oxidation state of the iron atom, tetrahedrally coordinated with the bridging sulfur atoms in the clusters. The fold (a sheet of four strands facing two helices) is shared among members of the family [4; 9]. Ferredoxin was for long associated with the fermentative chemistry of anaerobic organisms, but it is now agreed that they are ubiquitous in all domains of life, although the sequence identity is very low between the members of the family. Isoforms may have evolved not as generic electron shuttles but serve as selective couriers of valuable low potential electrons from selected electron donors to desirable electron acceptors [1]. Fuzzy oil drop (FOD) is an efficient method for the expression of a micelle-like hydrophobicity distribution in globular proteins [10]. It employs a 3D Gauss function to build a theoretical capsule (an ellipsoid) that encompasses the structure. This capsule models the shape of a globular protein in water with hydrophobic core surrounded by a hydrophilic shell but without the need for direct simulation of water molecules [11]. Such high symmetry and perfect following of this kind of distribution would render the molecule deprived of any form of biological activity except for high solubility. This phenomenon is observed in type III antifreeze proteins (AFPs). Their surface, which is covered by polar groups, opposes formation of ice crystals by affecting organization of surrounding water environment, directly contributing to survival of the cell at sub-zero temperatures [12]. Absence of exposed hydrophobic patterns drastically reduces ability of a protein to interact with other partners. A typical protein structure is however not that \"perfect\". Discrepancies in the distribution of hydrophobicity, where observed status of residues (due to their pairwise interaction) does not follow the 3D Gauss-based theory (entirely or partially), are a common occurrence [13; 14]. In particular, they become exceptionally apparent in amyloids [15; 16]. These peculiarities, appearing along the sequence (on the so-called hydrophobicity profile), are the foundation of structural and functional analysis of proteins using the FOD model. In this paper, we mainly discuss two ferredoxins--I (FdI) and II (FdII)--relatively small proteins (around 60 residues per chain)--with biological activity involving binding of a relatively large ligand and formation of a dimeric complex. They are a very interesting subject since they exhibit hydrophobicity distribution that is among the best in terms of accordance with 3D Gauss function we encountered so far, even stronger when compared to the aforementioned type III AFPs. Yet in contradiction to what FOD model would expect from them, these ferredoxins form complexes while AFPs do not. This warrants their more thorough investigation.