| Popis: |
The general physiology of catabolite repression of l-arabinose isomerase (l-arabinose ketol-isomerase, EC 5.3.1.4) in Pediococcus pentosaceus has been investigated. Particular emphasis has been placed on the regulation of enzyme formation as influenced by pentose or hexose metabolism. The capacity of cells to form the isomerase was found to vary widely with (a) the physiological age of the cultures and (b) the nature of the growth substrates. The early stages of growth on glucose, fructose and mannose, for example, were associated with complete repression of isomerase formation. This repression was released as the substrates became limiting for the growth of the organism. Cultures in a stationary phase of growth, however, rapidly lost the capacity to synthesize the isomerase unless a fresh supply of yeast extract or casein hydrolysate was added to the medium. Although some repression was noted, growth on ribose or xylose did not appear to result in the typical “glucose effect” repression observed when the hexoses were employed as growth substrates. As growth on the pentoses became limited by substrate depletion, a greatly stimulated capacity for isomerase formation was observed. These general observations were also noted during the formation of a galactose-induced s-galactosidase (EC 3.2.1.23). These results have been discussed in light of a recently proposed, tentative model for catabolite repression in this organism. |
