International Journal of Biological Macromolecules 62 (2013) 107–116 Contents lists available at ScienceDirect International Journal of Biological Macromolecules jo ur nal homep age: www.elsevier.com/locate/ijbiomac Further studies and biological activities of macromolecular protein R-Phycoerythrin from Portieria hornemannii Namasivayam Senthilkumar a,b,∗ , Chidambaram Kurinjimalar b , Ramar Thangam c , Veeraperumal Suresh d , Ganapathy Kavitha b , Palani Gunasekaran c , Ramasamy Rengasamy b a Department of Botany, Ayya Nadar Janaki Ammal College, Sivakasi, Tamilnadu, India b Centre for Advanced Studies in Botany, University of Madras, Guindy, Chennai, Tamilnadu, India c Department of Virology, King Institute of Preventive Medicine and Research, Guindy, Chennai, Tamilnadu, India d Department of Botany, Annamalai University, Annamalai Nagar, Chidambaram, Tamilnadu, India a r t i c l e i n f o Article history: Received 5 April 2013 Received in revised form 8 August 2013 Accepted 8 August 2013 Available online 17 August 2013 Keywords: Portieria hornemannii R-Phycoerythrin Thermo-stability property Antioxidant activity Anticancer activities Cell cycle distributions a b s t r a c t In the present study, the purified R-Phycoerythrin (R-PE) from a red alga Portieria hornemannii was sub- jected to the analysis of stability under the influence of different agents. Among the various inhibitors tested on R-PE EDTA at lower concentrations (<1 mM) supported the activity of R-PE. When R-PE was exposed to different organic solvents, ethanol supported the activity at the maximum followed by ace- tone, ethyl acetate, chloroform and methanol. Citric acid, as a preservative maintained the stability of R-PE both under 0 ± 5 ◦ C and 30 ± 5 ◦ C with 59.34% and 56.23% respectively, on 30th day. Thermal decom- position of the R-PE began near 60 ◦ C. Maximum weight loss was occurred between 150 ◦ C and 500 ◦ C. Complete weight loss was recorded around 875 ◦ C. Thermal denaturation was observed between 19 ◦ C and 40 ◦ C. Moderate to low antioxidant activities were observed in R-PE in relation to total antioxidant activities. After characterization, R-PE was taken for in vitro anticancer studies against selected cancer cell lines. Further studies involving AO/EB fluorescence staining and phase contrast microscope revealed characteristic apoptotic features like cell shrinkage, membrane blebbing, and nuclear DNA fragmenta- tion, etc. Likewise, FACS analysis revealed the cell cycle distribution pattern of A549 and HepG2 cells. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Phycoerythrin is a major light-harvesting pigment belonging to Phycobiliproteins of red algae. R-Phycoerythrin (R-PE) is an oligomeric protein of 240 kDa with 6  (about 16 kDa), 6  (about 21 kDa), and 1  (about 39 kDa) subunits [1]. R-PE is commonly used as a fluorescent label in immunology and cell biology [2,3] and in flow cytometry [4,5]. It is also used as a natural food dye [6] and as a marker in gel electrophoresis and iso-electrofocusing. The main applications of phycobiliproteins are as fluorescent markers of cells and macromolecules in biomedical research and natural colorant in food and cosmetics [7]. Phycobiliproteins are largely appreciated for their immuno-enhancing, anti-inflammatory, anti- carcinogenic, antioxidant and nutritive values [8]. ∗ Corresponding author at: CAS in Botany, University of Madras, Chennai, Tamil- nadu, India. Tel.: +91 9443854694; fax: +91 4144 238080. E-mail addresses: senthilkumarin@yahoo.co.in (N. Senthilkumar), thangam1985@yahoo.co.in (R. Thangam), veeraperumalsuresh@gmail.com (V. Suresh), profrengasamy@yahoo.com (R. Rengasamy). Phycoerythrins (PEs) are highly sensitive to variations in pH, salts, temperature, water stress and light [9–12], thus impeding the process of extraction, purification, storage and utilization. Prob- lems of storage stability of PEs can be minimized by ammonium sulphate precipitation or lyophilization. Metal ions are known to react with R-PE and they either promote or inhibit the R-PE activity [13]. Phycocyanin and Phycoerythrin are stable at low tempera- tures in the presence of preservatives like citric acid, in acidic and basic solutions and therefore, they could be utilized as food col- orant (chewing gum, jellies), health drinks, beverages and coloring agent in sweet, confectionery and cosmetics [14]. Citric acid as a preservative prevented the degradation of proteins [15]. Hepatocellular carcinoma and Lung carcinoma are the most prevalent forms of cancers reported across the globe. Although chemotherapeutic drugs can be quite effective in treating Hepa- tocellular carcinoma and Lung carcinoma, these agents do not differentiate normal, healthy cells from cancerous cells. Hence, there is a need for the development of therapeutic agents against Hepatocellular carcinoma and Lung carcinoma that can overcome drug resistance and reduce the toxicity on the host. Photodynamic therapy (PDT) is a useful and promising therapeutic method for 0141-8130/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ijbiomac.2013.08.004