ABSTRACT:The activity of (soluble acid) sucrase was detected in a culture medium of the cell suspension culture of watermelon (Citrullus vulgaris L.). A simple and rapid procedure for the identification and determination of extracellular sucrase from a culture medium of watermelon cell suspension cultures is described. Sucrose was used as a substrate for the determination of extracellular and intracellular activities of the enzyme. Intracellular activity was estimated from the cell suspension. The results show a 91.5-92.0% intracellular and 8.0-8.5% extracellular distribution of sucrase activity. The described method enables to carry out a rapid, simple and specific detection of extracellular sucrase in plants. 105 lus vulgaris cv. Samara as previously described by TILEMANN et al. (2003).Identification and determination of intra-and extracellular sucraseUsing sucrose as a substrate the intra-and extracellular activity of soluble acid sucrase was identified. Eight days old cell suspension cultures were used to determine the intracellular enzyme activity. The cells (5 g) were filtered and washed twice with 1,000 ml of distilled water. Soluble proteins were extracted by grinding the cells in a pre-cooled mortar using a ratio 1:2 (g/ml) of cells and Mc Ilvaine buffer pH 4.5 at 4°C. The homogenate was filtered through two layers of nylon cloth and centrifuged at 15,000 g at 4°C. For determinations of extracellular enzyme activity the cultivation medium (without cells) was used after centrifugation (15,000 g, 10 min at 4°C).
Enzyme assayEnzyme activity was determined by a modified method of RUBIO et al. (2002) using sucrose as a substrate. The reaction mixture contained a suitable amount of enzyme (0.2-0.4 ml) and 0.4 mM sucrose in Mc Ilvaine buffer pH 4.5 in a final volume of 2 ml. Enzyme activity was determined at 30°C for 30 to 60 min. The control contained temperature-inactivated enzyme (100°C, 10 min). The enzyme activity was expressed in katals. Proteins were determined by the method of BRADFORD (1976) using bovine serum albumin as a standard protein. The glucose content released by the enzyme was determined by the method of TRINDER (1969).
RESULTS AND DISCUSSIONSynthetic chromogenic substrates are very suitable for biochemical and histochemical studies of hydrolytic enzymes. In the last decades, several methods for the determination of hydrolytic enzymes have been developed. Various naturally occurring chromogenic substrates may be used for these purposes (KIM et al. 2002;MIČIETA et al. 2002). p-nitrophenyl-β-Dfructofuranoside and naphthyl-β-D-fructofuranoside were not synthesised and only a natural substrate -sucrose was used for the study of sucrase.Therefore only sucrose was used to study the activity of intracellular and extracellular (acid soluble) sucrase. The highest specific activity of the studied enzyme was recorded on day 8 of cultivation (Table 2) in undifferentiated cells. Homogenised cell suspension cultures and culture medium alone after 8-day cultivation were used to assay the activity of intrac...