Changes in Activities of Ribulosediphosphate Carboxylase and Phosphopyruvate Carboxylase during Leaf Growth of Tobacco.

Abstract

1) Water soluble proteins from leaves of tobacco (N. tabacum “Bright Consolation”. and corn (Zea mays) were fractionated by Sephadex G-100 column (2.5×40cm). Fraction 1 protein conteined ribulosediphosphate (RuDP) carboxylase (E.C.4.1.1.39) as well as phosphopyruvate (PP) carboxylase (E.C.4.1.1.31).
2) PP carboxylase was rapidly inactivated when incubated at above 25°. On the other hand, RuDP carboxylase was stable and the optimum temperature for the enzyme reaction was located at approximately 40°.
3) RuDP carboxylase activity of tobacco leaf on fresh weight basis, attained its maximum when the leaf elongated approximately 50% of its final length, and decreased rapidly thereafter towards leaf senescence.
4) There was a nearly parallel correlation between enzyme activities of RuDP and PP carboxylases and the content of fraction 1 protein of tobacco and corn leaves.
5) The activity of PP carboxylase of young corn leaf was as lower as that of young tobacco leaf, but PP carboxylase activity in matured leaves of corn was 15 times greater than that of tobacco leaves. The activity of RuDP carboxylase was generally lower in corn leaves, 40-70% to tobacco RuDP carboxylase, when compared with the same growth stages of a leaf.