We have purified to homogeneity, from mutant strains of Salmonella typhimurium, the small oligomers of porin that confer permeability channels to artificial vesicle membranes reconstituted from phospholipids and lipopolysaccharide. The molecular weights of the porin oligomers from the strains SH5551 and SH6017 appeared to be 130000 and 125000, respectively, and those of the monomers were 41 000 and 37 500, respectively, when determined by sedimentation equilibrium in the presence of dodecylsulfate. It was thus concluded that the functional porin oligomers consisted of three identical subunits. The Stokes' radius of the trimer . dodecylsulfate complex was around 5 nm. The trimer bound less dodecylsulfate than the monomer. The trimer . dodecylsulfate complex retained at room temperature the native conformation of porin, which is rich in fl-structure. When the trimers were dissociated further by various treatments, only the porin monomers were recovered in significant amounts, and the permeability-conferring activity was lost simultaneously. We propose, therefore, that the trimer is the minimal functional unit of porin that is capable of forming pcrmeability channels in the outer membrane of Salmonella typhimurium.The outer membrane of gram-negative bacteria allows a transmembrane diffusion of small hydrophilic substances of molecular weights less than 600 [1,2]. This selective permeability of the outer membrane was restored in the artificial vesicle membranes reconstituted from phospholipids, lipopolysaccharide and the outer membrane proteins [3] and the active components for channel formation were identified as proteins with molecular weights around 35 000, called 'porin' [4,5]. Since the permeation of the solute mediated by the porin showed no requirement for metabolic energy, little temperature dependency and poor stereospecificity for the solute, we have proposed that the permeation via this protein was mediated through waterfilled 'channels' [4].In our previous work, we isolated large aggregates of porin, called complexes I and 11, as active fractions for channel formation [4]. But the monomeric form of the porin, when produced by heating complex I or I1 in the presence of dodecylsulfate, no longer retained permeability-conferring activity in reconstituted ves-~~ ~~~~

Low temperature, 600~ annealing of LPCVD films was investigated using x-ray diffraction, ESR, TEM, and carrier mobility measurements. An optimum deposition temperature of about 550~ was found to yield good crystallinity and high electron mobility for annealed films; large grain sizes, a maximum crystallite size, and a maximum electron spin density were also observed for films deposited at the optimum temperature. The crystallite number was shown to be constant if the deposition temperature was below 570~ Electron spring density for the as-deposited films correlated with the crystalline volume by x-ray diffraction measurements on the films after annealing. This implies that only those amorphous components with high electron spin density can be converted into the crystalline phase by 600~ annealing.

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