STRUCTURAL HETEROGENEITY OF PSEUDOMONAS-AERUGINOSA BACTERIOFERRITIN

The subunit composition, amino acid sequence and haem-binding characte ristics of bacterioferritin (BFR) from Pseudomonas aeruginosa have bee n studied. Unlike other BFRs, P. aeruginosa BFR was found to contain t wo subunit types, designated alpha and beta, which differed considerab ly in their amino acid sequences. The N-terminal 69 and 55 amino acids of the alpha and beta subunits respectively were determined. The alph a subunit differed most from other BFRs. The two subunits were present in variable proportions in different preparations. The maximum stoich iometry of haem binding was found to be sample-dependent and to be dif ferent from the previously reported one per subunit [Kadir and Moore ( 1990) FEBS Lett. 271,141-143]. This previous haem-binding study was sh own to have been carried out with damaged protein, which contained bot h normal alpha and beta subunits and shorter versions of these that ap peared to have been produced by cleavage of the normal subunits. The p ossibility that aging processes degrade ferritins and affect their hae m-binding characteristics is discussed.