Porins are essential pore-forming proteins found in the outer membrane of several gram-negative bacteria. Investigating the relationships between molecular structure and function involves an. extremely time-consuming and labor-intensive purification procedure. We report a method for rapid extraction of the outer membrane protein, OmpF, from freeze-dried Escherichia coli cells using valeric acid, alleviating the effort and time in sample preparation. Extraction results in a highly enriched fraction containing OmpF as 76% of the total protein content. The apparent molecular mass determined by SDS-PAGE mobility was 38,900, similar to that of the monomeric form of OmpF. N-terminal sequencing yielded 23 amino acids with 100% identity to the published OmpF sequence. The trimeric form of OmpF was observed in unheated samples run on SDS-PAGE and analysis of these! samples by periodic acid/silver staining revealed the presence of unbound lipopolysaccharides. Furthermore, this method should prove useful for isolating other outer membrane proteins. (C) 2002 Elsevier Science (USA).