Activators of a trypsin-casein system isolated from old leaves of Ipomoea batatas

Activators of a trypsin-casein system isolated from old leaves of Ipomoea batatas

1994

A:PS

Trypsin in a casein substrate was activated by dialyzed water-extract from old leaves of sweet potatoes cv. Changhua. After purification by ammonium sulfate precipitation and column chromatography, 2 activator fractions, SPTA I and SPTA II, were obtained. SPTA II was homogenous, and SPTA I nearly homogenous, under urea PAGE. Using gel filtration on a Sephadex G-100 column, the MW of SPTA I was determined to be >100 000 Da and that of SPTA II about 100 000 Da. When 10 mg casein, 50 æg SPTA II and 20 æg trypsin were present in 2.5 ml of solution, 170% activation was observed, while increasing the amount of SPTA II to 150 æg increased activation to 1250%. The relative amount of activation decreased with increasing casein concentration. No similar activation of subtilisin or alpha-chymotrypsin was observed. Using haemoglobin as a substrate activated trypsin, but not as much as with casein. The activation of the trypsin-casein system was not due to the presence of Ca, precursors of proteinase, or additional substrate. It could be abolished by pretreatment of activators with heat or with alkaline solution, suggesting that native conformation is essential for activation to occur. Activation was countered by commercial Kunitz-type soyabean trypsin inhibitor. A relationship between activation energy and leaf-and-stem producing potential of cv. Changhua is proposed.

v.35(2):73-80, BOTANICAL BULLETIN OF ACADEMIA SINICA (NEW SERIES)

Research > Published Articles