COMPARATIVE-STUDIES OF TRANSGLUTAMINASE ACTIVITY AND SUBSTRATES IN DIFFERENT ORGANS OF HELIANTHUS-TUBEROSUS

Transglutaminase activity (TGase, E.C. 2.3.2.13), which binds polyamines to proteins, was previously found in etiolated apices ana activated slices of medullary parenchyma of Helianthus tuberosus L. cv. OB 1 tubers; in the present paper the activity was tested in mature leaves of the same plant and additional data were acquired on the above cited tissues. Flower buds were also examined and preliminary data is presented. The following parameters were analyzed: localization in the 22,000 x g supernatant or pellet fractions, dependence on pH, light, incubation time and different concentrations of Ca2+, EGTA, putrescine, endogenous substrates and casein and presence of a non-enzymatic activity. More than one enzyme or different forms of the same enzyme seem to be present in the same organ and its activity can be induced. An exogenous supply of Ca2+ is not absolutely required in any of the organs examined; however, its chelation reduces the activity. Multiple endogenous substrates seem to be present in the same organ, whereas casein is not recognized as a substrate. Results concerning the other parameters examined suggest the existence of organ-specific TGase activities. Their possible function in green and non-green tissues is discussed.