Extraction, partial purification and characterization of proteases from the red seaweed Gracilaria edulis with similar cleavage sites on κ-casein as calf rennet

Enzymes currently used in cheesemaking have various drawbacks, and there is a continual need to find new coagulants. This study describes the extraction and biochemical characterization of two proteases from the red alga Gracilaria edulis. The proteases were extracted with phosphate buffer and partially purified by ammonium sulphate precipitation and dialysis. The enzymes exhibited optimum caseinolytic activity at 60 °C and a pH range of 6-8. They showed a high ratio of milk-clotting over caseinolytic activity, indicating they had an excellent milk-clotting ability. The proteases were confirmed to be serine protease and metalloprotease with molecular weight (MW) of 44 and 108 kDa. They exhibited high hydrolytic activity on κ-caseins, cleaving κ-casein at four main sites, one of which being the same as that of calf rennet, which is the first reported for an algal protease. The findings demonstrated that the proteases could potentially be used as a milk coagulant in cheesemaking.

Gene cloning, expression and activity analysis of manganese superoxide dismutase from two strains of Gracilaria lemaneiformis (Gracilariaceae, Rhodophyta) under heat stress

Manganese superoxide dismutase (Mn-SOD) plays a crucial role in antioxidant responses to environmental stress. To determine whether Mn-SOD affects heat resistance of Gracilaria lemaneiformis, we cloned Mn-SOD cDNA sequences of two strains of this red alga, wild type and cultivar 981. Both cDNA sequences contained an ORF of 675 bp encoding 224 amino acid residues. The cDNA sequences and the deduced amino acid sequences of the two strains shared relatively high identity (more than 99%). No intron existed in genomic DNA of Mn-SOD in G. lemaneiformis. Southern blotting indicated that there were multiple copies, possibly four, of Mn-SOD in both strains. Both in the wild type and cultivar 981, SOD mRNA transcription and SOD activity increased under high temperature stress, while cultivar 981 was more heat resistant based on its SOD activity. This research suggests that there may be a direct relationship between SOD activity and the heat resistance of G. lemaneiformis.

Selenium and spermine alleviate cadmium induced toxicity in the red seaweed Gracilaria dura by regulating antioxidants and DNA methylation

The protective role of exogenously supplied selenium (Se) and polyamines (PAs) such as putrescine (Put) and spermine (Spm) in detoxifying the cadmium (Cd) induced toxicity was studied in the marine red alga Gracilaria dura in laboratory conditions. The Cd exposure (0.4 mM) impede the growth of alga while triggering the reactive oxygen species (ROS viz. O(2)(•-) and H(2)O(2)) generation, inhibition of antioxidant system, and enhancing the lipoxygenase (LOX) activity, malondialdehyde (MDA) level and demethylation of DNA. Additions of Se (50 μM) and/or Spm (1 mM) to the culture medium in contrast to Put, efficiently ameliorated the Cd toxicity by decreasing the accumulation of ROS and MDA contents, while restoring or enhancing the level of enzymatic and nonenzymatic antioxidants and their redox ratio, phycobiliproteins and phytochelatins, over the controls. The isoforms of antioxidant enzymes namely superoxide dismutase (Mn-SOD, ~150 kDa; Fe-SOD ~120 kDa), glutathione peroxidase (GSH-Px, ~120 and 140 kDa), glutathione reductase (GR, ~110 kDa) regulated differentially to Se and/or Spm supplementation. Furthermore, it has also resulted in enhanced levels of endogenous PAs (specially free and bound insoluble Put and Spm) and n-6 PUFAs (C20-3, n-6 and C20-4, n-6). This is for the first time wherein Se and Spm were found to regulate the stabilization of DNA methylation by reducing the events of cytosine demethylation in a mechanism to alleviate the Cd stress in marine alga. The present findings reveal that both Se and Spm play a crucial role in controlling the Cd induced oxidative stress in G. dura.

[Purification and characterization of a bromoperoxidase from Gracilaria lemaneiformis]

A bromoperoxidase from Gracilaria lemaneiformis was purified to homogeneity using a multi-step process of ammonium sulfate precipitation (AS), dialysis, and DEAE-cellulose 52 anion exchange chromatography. The bromoperoxidase activity was unstable or undetectable in crude extract solution. However, it became stable with electrophoretic purity after this multiple purification process. The anion exchange chromatography purification was a critical step in the purification process, which effectively eliminated the phycobiliprotein and smucilaginous polysaccharides. The purified bromoperoxidase was a monomeric enzyme with the relative molecular masses of 66 kD as determined by denaturing and native gradient gel electrophoresis. The optimal pH for bromoination was 6.0 and bromoperoxidase activity was stable as stored at a broad pH range of 3.0-9.0. Of a range of compounds tested, only vanadium enhanced bromoperoxidase activity. Kinetic studies for the bromination of monochlorodimedone (MCD) showed that the Km values of Br- and H2O2 are 53.5 micromol/L, 38 micromol/L respectively.

Different regulation of haloperoxidation during agar oligosaccharide-activated defence mechanisms in two related red algae, Gracilaria sp. and Gracilaria chilensis

The related red seaweeds Gracilaria sp. from the eastern Mediterranean and Gracilaria chilensis from Chile were similar in their enzymatic inventory for halogenation. In both species, halogenation was dependent upon H(2)O(2) and thus driven by haloperoxidases. These could be inhibited with phosphate and reversibly inhibited with azide and were therefore apparently dependent upon vanadate. Both species generated in the first line bromoform and other brominated halocarbons. Gel electrophoresis under non-denaturating conditions demonstrated that both species expressed halogenating peroxidases. Elicitation of Gracilaria sp. with agar oligosaccharides resulted in marked increases in bromination, iodination, and chlorination. Production rates of volatile halocarbons and phenol red bromination both increased by a factor of eight, presumably due to increased availability for haloperoxidases of H(2)O(2) during the oxidative burst response. Elicitation of Gracilaria sp. also triggered a release of bromide ions through DIDS-sensitive anion channels, which allowed for some bromination in bromide-free medium. However, this effect was relatively limited. By contrast, agar oligosaccharide oxidation in G. chilensis did not increase halogenation. Obviously, agar oligosaccharide oxidation does not provide sufficient amounts of hypohalous acids for such increases, because it does not deliver H(2)O(2) at the active site of vanadium-dependent haloperoxidases. These results correlate with earlier findings that the agar oligosaccharide-elicited oxidative burst controls microorganisms while agar oligosaccharide oxidation does not.

In vitro assay and light regulation of nitrate reductase in red alga Gracilaria chilensis

Nitrate reductase (NR) is the first enzyme in the nitrogen assimilation pathway. The in vitro NR activity of Gracilaria chilensis was assayed under different conditions to reveal its stability and biochemical characteristics, and an optimized in vitro assay is described. Maximal NR activities were observed at pH 8.0 and 15 degrees C. The apparent Km value for NADH was 8 microM and for nitrate 680 microM. Crude extracts of G. chilensis stored at 4 degrees C showed a 50% decrease of NR activity after 24 h. The highest NR activity value (253.20+/-2.60 x 10(-3) U g(-1)) was obtained when 100% von Stosch medium (500 microM NO3-) was added before extraction of apical parts. Algae under light:dark cycles of 12:12h exhibited circadian fluctuation of NR activity and photosynthesis with more than 2 times higher levels in the light phase. No evidence of endogenous diel rhythm controlling NR activity or photosynthesis was observed. Light pulses lasting 10 or 60 min during the darkness increased the NR activity by 30% and 45%, respectively. The results indicate that NR and photosynthesis are regulated mainly by light and not by a biological clock.