Cell Envelope and Shape of Escherichia coli K12.

The protein from Escherichia coli ghosts can be separated electrophoretically into three major bands (I, II, and IV) and one minor band (III). The proteins corresponding to bands I, II and IV have been isolated. Protein IV is the lipoprotein described previously by Braun et al, and is thus a homogeneous polypeptide chain. Proteins I and II do not contain phosphorus, palmitic acid, or lipopolysaccharide but small amounts of carbohydrate, probably glucosamine ((or a derivative). Proteins I and II have been characterized by amino-acid analyses, tryptic fingerprints, carboxypeptidase digestion, and cyanogens bromide cleavage. Based on cysteic acid the minimum chemical molecular weights of both proteins are the same as those found by electrophoreses: about 40000 (-,+ ≈ 10%) for I and about 28000(-,+ ≈ 10%) for II. The numbers of tryptic peptides found do not argue against the assumption that each of the two proteins consists of identical polypeptide chains. However, the sum of the apparent molecular weights of the cyanogens bromide fragments of protein Is almost 80000. the amino acids liberated by carboxypeptidase A at near integral values per 40000 g of protein I correspond to 1 mol each of serine, glycine, alanine, isoleucine, tyrosine, phenylalanine, and to 2 mol valine per 40000 h of protein; however, only 0.5 mol leucine is released. Apart from revealing a rather hydrophobic C-terminal region, the data thus include the possibility that protein I consists of two different but presumably rather similar polypeptide chains. Protein II is a typtic fragment of protein II* with a molecular weight near 40000. Protein II* can give rise to two other fragment by the action of other proteases. The apparent molecular weights of the cyanogen bromide fragments of protein II add up to that of protein II. However, although carboxypeptidase A liberates nearly 1 mol each of serine, alanine, valine, and leucine per 28000 h of protein II, it releases only about 0.5 mol each of glutamic acid, glycine and isoleucine. As for protein I, it cannot yet be excluded that protein II consists of two polypeptide chains. If so, the two must be very similar. Regardless as to whether proteins I or II consist of one or two polypeptide chain these must be arranged as repeating subunits in the outer membrane of the E.coli cell envelope. The properties of proteins I and II allow them to be classified as intrinsic or integral membrane proteins. [ABSTRACT FROM AUTHOR]