Alcohol dehydrogenase activity in isolated vacuoles of red beet root cells
The main localization place of alcohol dehydrogenase (ADH, KF 1.1.1.1) in plant cells is considered to be the cytosol. However, a rather high activity of this enzyme in the acetaldehyde reduction reaction (reduction reaction) was found in fractions of vacuoles isolated of red beet root cells. Despite the fact that the activity of ADH in the reduction reaction in vacuoles was quite high (on the average, 160 nM NADH / mg protein), the activity of ADH tissue extracts markedly exceeded it (on the average, 300 nM NADH / mg protein). The specificity of the enzymatic reaction was indicated by the results of inhibitory analysis. Complete suppression of ADH activity occurred in the presence of 1.10-phenanthroline, para-chloromercuribenzoate. 2-Mercaptoethanol also had an inhibitory effect. The pH optimum for the enzyme in reduction reaction was pH 9.0, and in ethanol oxidation reactions (oxidation reaction) was pH 8.0. The results of the study of enzymatic activity in PAGE after electrophoresis demonstrated two isoforms of ADH in the vacuolar fractions and three isoforms in the tissue extract. The limiting factor for ADH activity may be the absence of cosubstrate NAD(H). For isolated vacuoles, a relatively high concentration of NADH (3.01 nM NAD (H)/mg protein) was established, compared to tissue extract (2.75 nM/ mg protein). The results indicate the possible functioning of ADH in the plant cell vacuoles, mainly as an aldehyde-reducing enzyme.