Shikimate dehydrogenase, activity

Shikimate dehydrogenase The use of modified buffer increased the specific activities (S.A.) of this enzyme in the soluble supernatant preparations about sixfold (from 3.0 to 20.3). In addition, activity not otherwise measured in the homogenized pellet was found there with the use of modified buffer. In modified buffer shikimate dehydrogenase activity (e.g.,... 

The inset shows that if cells were maintained continuously in exponential phase, then shikimate dehydrogenase activity leveled off after eight generations to a lower activity than was ever reached in ordinary subcultures. It will be interesting to see whether stationary-phase cultures might yield a cytosolic form of shikimate dehydrogenase that has not been seen in extracts thus far studied from exponential-phase cells. 

Cole al. (72) found that glyphosate increased extracted specific activities of two shikimate pathway enzymes, shikimate dehydrogenase (shikimate NADP oxidoreductase. Figure 3, No. 

Plants contain shikimate dehydrogenase (shikimate NADP oxidoreduc-tase) which reversibly interconverts dehydroshikimate and shikimate [Fig. 2 (4)]. The enzyme has been detected in a number of plant sources (Balinsky and Davies, l%la Yoshida, 1969). Unlike the microbial enzyme which is specific for NAD, the plant enzyme is specific for NADP (Balinsky and Davies, 1961b). Anthranilic acid and hydroxybenzoic acids inhibit the reaction in the direction of shikimate dehydrogenation (Balinsky and Davies, 1961b). The significance of the inhibition in controlling the activity of the pathway is unknown. 

Results similar to those obtained with shikimate dehydrogenase were obtained with prephenate aminotransferase (Fig. 7). High levels of enzyme activity that were present in stationary phase declined upon dilution into fresh medium, reaching a low point during exponential phase. 

Fig. 6. Variation of the levels of shikimate dehydrogenase in N. silvestris during the various growth phases following subculture from cells in stationary phase. The inset shows the constant and reduced levels of activity obtained from cultures maintained continuously in exponential phase (data shown for the 8-to-ll generation interval).

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