Acta Biologica Tomus XXIX. Fasciculi 1-4. [antikvár]

Acta Biol. Szeged. 29 (1—4), pp. 3—9 (1983) THE CHARACTERISTICS OF ASPARTATE TRANSAMINASE ENZYME IN TOBACCO TISSUE CULTURES I. Gaal and Erzsébet Köves Depart ment of Plant Physiology, AttUa József University, Szeged (Received September 10, 1982) Abstract The optimal temperature of the activity of the aspartate transaminase enzyme obtained from tobacco tissue cultures is 53°C at 8.5 pH. The activation entalpy of the reaction is 33.5 KJ, Km = l.I5.10-^M on aspartate. The reaction does not require pyridoxal phosphate. Fe'+, Co-"^, Ni-"*", Mn-"*" do not influence the enzyme activity. Cd-+, Hg-+, Zn2+, Cu-+, Ag+, semicarbazide hydroxylamine, parachlor-mercurybenzoate inhibit the reaction. There is correlation between the inhibitory effect and the electron structure of the metal ions. Aspartate transcminase activity is measurable in every culture, while in the case TRP substrate transamination is only detectable in the so-called habituated cultures. Key words: Aspartate transaminase, tryptophan-transaminase, tobacco callus, ion effect, enzyme inhibition, Nicotiana tabacum cv. Xanthi. Abbreviations: ASP = aspartate, DNFH = dinitrophenylhydrazine, GLU = glutamic acid, GOT = glutamic acid-oxaloacetic acid-transaminase, lAA = -indoIe-3-acetic acid, PCMB = parachlor-mercurybenzoate, TRP=tryptophan. Introduction The aspartate transaminase (Smith and William, 1951) is one of the mostly studied enzymes among the plant-transaminases. It participates in the metabolism of amino acids (Fowden, 1967), takes part in the pathway of the glyoxylic acid (Toll-bert and Yamazaki, 1969), the C4-reaction pathway, and the intercellular transport of the metabolites (Hatch, 1971), It catalyzes the transformation of tryptophan in to indole-3-pyruvic acid from which indole-3-acetic acid is formed (Gordon, 1961; Larsen, 1967; Schneider et al., 1972; Herkloss and Libbert, 1976). Certain metal ions influence the activity of the enzyme (Happold and Turner, 1957; Nadkarni and Kamala, 1962; Patwardhan, 1960; Verjee and Evered, 1969). Latter authors studied the influence of metal ions on the enzyme in diff'erent plants. The obtained results are contradictory in many cases. In our opinion the contradictions cannot be fully explained by the variations in species. Examination of certain substances and physiological processes in plant segments is very complicated due to the differentiation of the cells, since the tissues of various structures may react differently from the meris-tematic cells. Morphologically and physiologically the cell- and tissue cultures are homogeneous systems. Their cells are dedifferentiated. The keeping under sterile conditions of the tissue cultures is also easier and more controllable, therefore, it seemed reasonable to study a few basic characteristics of this important enzyme in tobacco callus culture. Since the role of the enzyme in the auxin synthesis also belonged to our range of interest, in one series habituated callus cultures capable of auxin synthesis were used, and normal callus cultures not growing without auxin were used in the other experiments. As the enzyme transforms aspartate with a rate of nearly two ordes 1 ¦'I- 1 ; , i ^ ' V,' • i!' r' f;/ 1'' r'' fii