The Occurrence and Properties of Alkaline Invertase in Mature Roots of Sugar Beets

抄録

Alkaline invertase activity was hardly detectable in immature sugar beet roots, but appeared when the roots began to develop and simultaneouly to synthesize sucrose, and thereafter, increased parallel with sucrose accumulation. Conversely, acid invertase activity was very high in immature roots, but rapidly decreased before sucrose was stored, and was hardly detectable in mature roots.
Alkaline invertase was partially purified from mature roots by procedures including ammonium sulfate fractionation, DEAE-cellulose column chromatography, Sephacryl S-300 gel filtration, and ECTEOLA-cellulose column chromatography. Alkaline invertase consisted of two forms (enzymes I and II) which were separated by DEAE-cellulose column chromatography. Relative molecular weights of both enzymes obtained by gel filtration on Sephacryl S-300 were the same, and were estimated to be 280, 000. Their pH optima were in the vicinity of 8.0. The Km value for sucrose of enzyme I was 33.3 mM and enzyme II showed a biphasic curve in Lineweaver-Burk plots. Both enzymes I and II hydrolyzed sucrose, but could not hydrolyze raffinose, maltose, or p-nitrophenyl-α-D-glucoside. Changes in their activities during development of roots showed different patterns. The roots had a high activity of enzyme I during sucrose accumulation and the enzyme rapidly decreased when sucrose reached a constant level, while the level of enzyme II activity was approximately constant.