Identification and characterization of a super-stable Cu-Zn SOD from leaves of turmeric (Curcuma longa L.)

We report a novel super stable superoxide dismutase (SOD) extracted from the leaves of Curcuma longa L.-a post-harvest waste. The scavenging activity of this SOD remains intact both in crude and purified forms before and after heating at boiling temperatures (80-100 degrees C) up to 20 min, autoclaving (6-20 bars up to 10 min) and microwaving (frequency of 2,450 megahertz (MHz) or million cycles per second for 1-3 min). This SOD has significant shelf life at room temperature (25-35 degrees C) and is stable for at least 18 months at 4 degrees C and with the retained activity of 82% at -10 degrees C and 88% at -20 degrees C without any infection or contamination. The heat stable enzyme is present both in cytoplasm and chloroplasts. The enzyme is also stable under wide range of pH, alcohol and SDS concentrations. The heat stability of this SOD protein is not due to any associated phenolic compound as no phenolic compound was bound to the novel thermo-stable SOD. The activity staining through native PAGE and purification of the enzyme protein have shown that this form of enzyme has a native molecular weight of 30.8 kDa and has two subunits of 15 kDa as shown by SDS PAGE. The characterized novel isoform is a Cu-Zn SOD as is indicated by its sensitivity to both H2O2 and KCN. Indian, US and PCT patents have been filed and products are being developed using this hyperthermophilic enzyme.

Analysis of photocontrol of aspartate kinase in barley (Hordeum vulgare L.) seedlings

Aspartate kinase (AK) activity is regulated by light. The activity was more in light exposed barley seedlings than those grown in the dark. The light effect was manifested even with small exposures of 5 min duration and red light was more effective than white light in this respect. The effect of 5 min red light could be reversed by a 5 min pulse of far-red light indicating the involvement of phytochrome in this response. The phytochrome is also involved in long term light effects (24 hr exposures with white light). Ca++ takes part in the signal transduction pathway for this light response. Western blot analysis using antibodies raised against the purified lysine- and threonine-sensitive AK isoenzymes from spinach leaves showed no cross reaction with the antibodies to the threonine-sensitive AK in the dark and 5 min far-red light exposed seedlings. But the protein band was detected in the white and red lights. Northern blot analysis of seedlings grown under dark and exposed to white, red and far-red lights and probed with the gene encoding aspartokinase-homoserine dehydrogenase (AKHSD) protein indicated that the gene was differentially expressed. In dark grown seedlings, AKHSD transcript was in low concentration as compared to white light where the transcript concentration was high. A 5 min red light pulse increased the transcript concentration significantly in contrast to 5 min far-red light. The transcript concentration was reduced when 5 min red light was followed by a 5 min far-red light pulse. The AK activity in dark-raised seedlings is attributed to the presence of only one isoenzyme that is sensitive to lysine but insensitive to Ca++ and calmodulin (CAM). In both white and red light exposed seedlings, three isoenzymes of AK were detected. Two of these were sensitive to threonine while one was sensitive to lysine. Both of the threonine sensitive isoenzymes were activated by Ca++ and CAM. Also one of these isoenzymes seems to be located and synthesized in chloroplasts because its synthesis was completely inhibited by chloramphenicol but not by cycloheximide.

Subunit structure of lysine sensitive aspartate kinase from spinach leaves

The lysine-sensitive isoenzyme of aspartate kinase was purified to homogeneity from spinach leaves and its subunit composition was studied. The purified preparation had an apparent molecular mass of 280,000 and separated into two subunits- a large subunit with molecular mass of 53,000 and smaller subunit with molecular mass of 17,000 by urea treatment and SDS PAGE. The enzyme molecule has subunit composition of 4 large and 4 small subunits. The activity of the large subunit was stimulated more than two fold by the addition of small subunit and the stimulated activity was inhibited by EGTA. This inhibition could be reversed by Ca++. Further characteristics of the smaller subunit such as heat stability, behavior on ion exchange chromatography, elctrophoretic mobility on polyacrylamide gels, amino acid composition and pattern, presence of trimethyl lysine, its ability to activate other calmodulin stimulated enzymes and its calmodulin-like nature in RIA tests suggested that this subunit is identical to calmodulin.

Purification and characterization of homoserine dehydrogenase from spinach leaves

Homoserine dehydrogenase (HSDH) has been purified to homogeneity from spinach leaves using ammonium sulphate fractionation followed by ion exchange chromatography, gel filtration and FPLC techniques. The purified enzyme has a relative molecular mass of 220,000 and subunit molecular mass of 55,000 and probably occurs as a tetramer. The enzyme was found to be sensitive to threonine and also exhibited aspartate kinase (AK) activity, which was also sensitive to threonine suggesting that it is a bifunctional protein. The enzyme protein also gave a positive cross reaction with antibodies raised against purified AK isoenzymes. Both HSDH and AK activities were stimulated by calcium and calmodulin.

Lysine- and threonine-sensitive aspartokinase isoenzymes from spinach leaves share common antigenic determinants

The lysine- and threonine-sensitive isoenzymes of aspartate kinase were purified to homogeneity from spinach leaves and polyclonal antibodies were raised in rabbits. The antibodies were characterized by various immunological tests like Ouchterlonys-double-diffusion, titrations of the inhibition of enzyme activity and ELISA. The antibodies against the lysine-sensitive isoenzyme could recognise as little as 50 ng of the pure antigen protein and that against the threonine-sensitive form could recognise 200 ng of the protein in the ELISA tests. The immunological tests have also shown that the lysine and threonine sensitive isoenzymes of aspartate kinase share some common antigenic determinants and differ in others.

Detection of aspartate kinase in rat liver and its activation by Ca++ and calmodulin

The enzyme aspartate kinase (EC 2.7.2.4) has been detected in rat liver (animal tissue) for the first time. This enzyme, like the aspartate kinase from bacteria and plants is inhibited by lysine and threonine. Further, the activity of the enzyme is stimulated over two fold by Ca++ and calmodulin and inhibited by EGTA, a Ca++ chelator and trifluoperazine, an anti-calmodulin compound.

An analysis of the action of light on betalain synthesis in the seedling of Amaranthus caudatus, var. viridis

Accumulation of betalain (amaranthin) in the seedling of Amaranthus caudatus, var. viridis, is inducible by light. Since the apparent lag-phase of amaranthin accumulation after the onset of light is of the order of 3 h, light induction experiments could be performed up to 3 h after the onset of light without interference with actual synthesis. The intricate induction phenomena can be explained as follows: The inductive light operates through phytochrome and through a blue/UV photoreceptor ('cryptochrome'). A phytochrome-dependent 'High Irradiance Reaction' is of minor importance. However, there is a strong, specific interaction between the light effects mediated through phytochrome and cryptochrome in the sense that the 'extent of the reversible response' - (response obtained with a particular light treatment terminated with a saturating red light pulse) minus (response obtained with the same light treatment when terminated with a saturating 756 nm light pulse) -increases with increasing Pfr level and total fluence rate during the induction period. It is concluded that light induced amaranthin synthesis is, in fact, a convenient biochemical model system of photomorphogenesis in the case when phytochrome and cryptochrome operate simultaneously in mediating photomorphogenesis.

Effect of Auxins and Light on Rooting Stem Cuttings of Populus nigra Salix tetrasperma, Ipomea fistulosa and Hibiscus notodus in Relation to Polarity

The apical and basal ends of stem cuttings of Populus nigra, Salix tetrasperma, Ipomoea fistulosa and Hibiscus notodus were treated with 10 mg/l solutions of IAA and IBA for 24 hours and were planted either erect or inverted both in light and dark. Observations for the number of cuttings that rooted and the roots produced on them were recorded at weekly intervals. In Salix, Ipomoea and Hibiscus rooting was more on cuttings planted erect, while in populus it did not differ much with the manner of planting. The reduced rooting in inverted cuttings may be ascribed to the low level of endogenous auxin at the apex due to polar transport. An exogenous application of auxins enhanced rooting on inverted cuttings. In dark, roots on Populus and Salix cuttings were produced both above and within the rooting medium. The weak polarity of these two plants may be due to the potential root primordia reported in their stem. The formation of callus occurred on the top of Populus cuttings whether planted erect or inverted but it differentiated into branches on erect cuttings only. In those planted in an inverted position the callus failed to differentiate in spite of the application of kinetin, auxins, TIBA, coumarin and sucrose, and dried ultimately.