The extracellular form of the K5 polysaccharide was produced, purified and characterized from a strain of Escherichia coli, the maximum fermentation yield (320 mg/L) was obtained after 15 h. The polysaccharide, recovered by precipitation with cold ethanol (80%), was purified through a pro cess employing an enzymic deproteination step using fungal protease. Charac terization by TLC and GC chromatography revealed that the K5 was mainly composed of glucuronic acid and N-acetyl-glucosamine. The 13C-NMR spectrum showed the product's structure to be the same as that of the K5 capsular polysaccharide described in the literature.

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An investigation was made of the molecular weight of the Escherichia coli antigenic K5 polysaccharide. Two components with molecular weights of 16,000 and 1,500 were observed. The ratio of these two components depended on a lyase produced by the same E. coli. This lyase acts by a β-elimination mechanism to depolymerize the K5. At the end of the fermentation the thermally treated (to inactivate the lyase) and untreated twenty-four-hour-old cultures each contained two K5 components of different Mw, in different ratios. The two components were monitored over a fermentation time-course. "3C-NMR spectrometry was employed to verify the lyase mechanism of action.