Bacfer

Bacfer, 36 414-415, 449-451 amino acid sequences, 36 468 Fe Mossbauer spectroscopy, 36 423... 

Bacterial leaching, minerals, 36 115-121 laboratory reactors, 36 116-117 monitoring organism growth, 36 117-119 nutrient effects, 36 119 pH control, 36 121 toxicity effects, 36 119 Bacterioferritin, see also Bacfer cluster, 43 362-363... 

Ferritin, 36 449-451, 43 363, 399-400 amino acid sequences, 36 465-467 bacterial, see Bacfer biochemistry, 36 450-451 dimer and larger cluster formation, 36 479-481... 

Hemes, see also Ferric hemes Ferrous hemes in bacfer, 36 429... 

Pseudomonas aerogenes ferredoxin, 33 55-56 Pseudomonas aeruginosa bacfer iron cores, 36 452 diheme cytochrome c peroxidase, 36 242-245... 

One striking similarity between iron metabolism in animals and bacteria is that both contain ferritin (63). Bacterial ferritin, or bacfer, resembles ferritin in a number of respects (Section IV), but a key difference is that bacfer is also a 6-type cytochrome (129), cytochrome bi (126). Thus the question arises Is it primarily a cytochrome or primarily an iron storage protein This question opens up a large number of avenues of research, some of which are described in Section IV, that we believe will help define further how animal ferritin functions. One important area is that of genetic control of bacfer expression. 

The idea that in vivo bacfer may serve as an electron store has been investigated by Fe Mossbauer spectroscopy. Cells of P. aeruginosa grown to the stationary phase on Fe-enriched media were shown to contain bacfer in which at least 90% of the iron was oxidized (72). Therefore, bacfer is unlikely to act simply as an electron store. 

A final point on the function of bacfer is that, given it contains a high level of phosphate (Table II) when loaded with iron, one of its roles may be as a phosphate store. 

A high-resolution X-ray diffraction structure of bacterial ferritin is not yet available but it is clear from molecular weight measurements, sedimentation velocities, and low-resolution X-ray data that bacterial ferritin consists of 24 subunits of molecular weight 18,000-21,000, depending on the source 63). The overall diameter of . coli bacfer is 119-128 A, consistent with this protein having the same general shape as animal ferritin. 

Escherichia coli bacfer consists of a single type of subunit 4, 156), but P. aeruginosa bacfer consists of at least two types of subunits whose relative proportions vary with growth in a manner yet to be defined 73). Azotobacter vinelandii bacfer also has two types of subunits 60). 

The X-ray structure of horse spleen ferritin reveals that each of the subunits is based on a 4-a-helical bundle type of super-secondary structure (46). This is also likely to be the type of structure of the bacfer subunits, given the overall similarity of the two types of ferritins (63). This view is supported by the secondary structure prediction analysis for E. coli bacfer reported by Andrews et al. (5). 

The EPR and electronic spectra of the heme of bacfer are not significantly affected by the presence of the nonheme iron core (30, 73). Thus the redox potential difference of the heme iron in apo- and holobacfer (145) (Table II) is most probably caused by a long-range electrostatic effect of the core charge. This indicates that the core carries an overall... 

Some of the characteristics of the nonheme iron cores of ferritins and hacfers are given in Table II. As can be seen there is a wide variation in properties, though these do not seem to depend solely on overall core size. The mean core diameters measured by electron microscopy for human ferritin (84) and P. aeruginosa hacfer (100) were found to he 70-75 and 60-65 A, respectively, with, in both cases, a distribution of sizes between 55 and 80 or 85 A. The maximum core attainable for human or horse ferritin corresponds to 4500 atoms of Fe per molecule (49), or —33% of the mass of the fully loaded protein. The bacfer core contains less iron and thus is considerably less densely packed. 

The ease with which the core of ferritin and bacfer can be reconstituted with Fe and an oxidant has led to work with Fe and other metals. Fe, added as a citrate, oxalate, or nitrilotriacetate complex, to horse holoferritin does enter the core, but only a small amount of Fe is taken up (139). No Fe + was taken up by apoferritin. This work emphasizes the requirement for core formation to occur by the oxidation of Fe +, a subject we discuss in the following section. 

The uncertainty concerning the mechanism of iron release in vitro is mirrored by the mechanism in vivo. Assuming that, in vivo, released iron is Fe +, many authors have attempted to identify the physiological electron donors. Because FMNH2 leads to rapid in vitro iron release (52, 70,123,142), this has been cited as a potential physiological donor (142), but the amount of free FMNH2 in cells is very low. Therefore, attention has begun to turn to flavoproteins (8) and to protein-mediated reduction (see the next section). This is one of the areas in which we believe work with bacfers can yield important results. 

Watt et al. (146) have also proposed that protein-mediated electron transfer reactions with ferritin may be physiologically important. They studied the core oxidation of reduced A. vinelandii bacfer and... 

Interestingly, the difference in redox potential between the heme of apobacfer and the core of holobacfer is —250 mV 145), which is comparable to the difference in redox potential between cytochrome 65 and the core of ferritin of —190 mV. It may he in both cases that the heme accepts electrons from the growing core when the incoming Fe + is oxidized to Fe +. If this is so, the marked reduction in the redox potential of the heme of bacfer once the core is partially loaded could act as a control to ensure that some of the core iron remained in the Fe state, or even to limit the growth of the core. 

Work with bacfer has not progressed to the stage at which rate constants have been reported, but it is clear that a variety of hemopro-teins can oxidize reduced bacfer, with rates for the bacfer heme oxidation considerably greater than those for the core oxidation (F. H. A. Kadir and G. R. Moore, unpublished observations). 

Fig.l. Gas chromatograms (GC) of the methyl ester products converted from a-linolenic acid by Clavibacter sp. ALA2. (A) Bioconversion of a-linolenic acid by Clavibacter sp. ALA2. Peak I the product with GC retention time (Rt) of 18 min Peak II the product with GC Rt of 26 min. (B) Incubation of a-linolenic acid with autoclaved C/av/bacfer sp. ALA2. 

Fig. 5. Bioconversion of n-3 polyunsaturated fatty acids by C/av/bacfer sp. ALA2.

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