5-Dehydroshikimate reductase in the tea plant (Camellia sinensis L.). Properties and distribution.

1. A method for the extraction of 5-dehydroshikimate reductase (EC 1.1.1.25) from tea plant tissues in an active soluble state has been developed. It is dependent on the use, in the extraction medium, of an insoluble polyphenol adsorbent (Polyclar AT), which prevents the polyphenols present from precipitating all the proteins. 2. The enzyme has the following properties: pH optima at pH10.1 in glycine-sodium hydroxide buffer and at pH7.7 in tris-hydrochloric acid buffer; K(m) (NADP) 32mum and K(m) (shikimate) 0.43mm; and NADP-specificity. It was completely inhibited by 0.33mm-p-chloromercuribenzoate and this inhibition was completely reversed by 10mm-cysteine. Iodoacetate and arsenite inhibited the enzyme to a smaller extent. 3. The specific activity of the enzyme was higher in the parts of the actively growing shoot tips (third leaf>stem>second leaf>first leaf>bud) than in the mature leaves. However, the mature leaves had the greatest total activity. 4. The importance of these findings with respect to flavanol biosynthesis in tea plants is discussed.