Poly-γ-glutamic acid

Abstract

We investigated the functionality of(γ-PGA), which is produced by Bacillus subtilis D7, for its potential applications in medicine and cosmetics. The γ-PGA had angiotensin-converting enzyme (ACE) inhibition activity. ACE inhibition activity was dependent on the γ-PGA concentration; the highest ACE inhibition activity was observed at 1.25 mg/l of γ-PGA. IC50 (0.108 mg/ml) of the γ-PGA was lower than that of standard ACE inhibitory drug, N-[(S)-mercapto-2-methylpropionyl]-L-proline (0.247 mg/ml). The γ-PGA also had water-holding capacity and hygroscopicity. Furthermore, the γ-PGA inhibited growth of some pathogenic bacteria, including Listeria monocytogenes, Salmonella typhimurium, Staphylococcus aureus, Klebsiella pneumonia and Esherichia coli. The γ-PGA exhibited a good metal adsorption capacity; Cr (VI) adsorption capacity of γ-PGA increased with decreasing pH, and the maximal adsorption was observed at pH 2. Our results suggest that γ-PGA may be expected to be widely applied in cosmetics, biomedical and environmental industries with the feature of being less harmful to humans and the environment.

1. Introduction
Poly-γ-glutamic acid (γ-PGA) is produced by a number of species of Bacillus. It is an unusual anionic polyamide that is made of d- and l-glutamic acid units connected by amide linkages between α-amino and γ-carboxylic groups. The γ-PGA is biodegradable, edible, water-soluble and non-toxic to humans and environment. Therefore, it has been suggested for use as biodegradable plastics (Tsutomu and Makoto, 2002), flocculants (Bajaj and Singhal, 2011), biological adhesive (Otani et al., 1996) and food additives (Lee and Kuo, 2011). For example, flocculating activity of the γ-PGA produced by Bacillus licheniformis CCRC 2826 (Shih et al., 2001) or Bacillus subtilis R23 (Bajaj and Singhal, 2011) has been reported. Some researchers also reported that the γ-PGA could adsorb basic dyes (Inbaraj et al., 2006).

Hypertension is a common progressive disease leading to several diseases such as cardiovascular disease, stroke and diabetes. Angiotensin-converting enzyme (AC) is a key component in rennin angiotensin aldosterone system which regulates blood pressure (Balasuriya and Rupasighe, 2011). Inhibition of ACE is a basic approach in the therapy of high blood pressure in humans. Therefore, screening of potential ACE inhibitors is expending broadly. ACE inhibitory peptides have been found in many different food proteins; milk casein, gelatin, corn gluten, fish proteins and Korean traditional fermented foods (Doenjang, Kanjang) (Ariyoshi, 1993). ACE inhibitory peptides derived from these food proteins have great potentials in the development of a novel functional food and drug for preventing hypertension and therapeutic purposes. If ACE inhibition activity of the γ-PGA was identified, it could be utilized as a new and harmless drug, since it is edible and nontoxic toward humans. However, there is no report on the ACE inhibition activity of the γ-PGA. On the other hand, exposure to external factor, i.e., air humidity, ultraviolet radiation and temperature, as well as endogenous factors, i.e. hormones, may disrupt skin balance between the water content and lipids on skin. In addition, there is common use of soaps, detergents and hot water disrupting skin balance (Dal`Belo et al., 2006). These factors may cause dry skin as well as atopic dermatitis on skin in severe case. Moisturizers not only increase the skin`s water content but also protect the skin and encourage an orderly desquamation process that makes the skin appear smoother. From the cosmetic point of view, therefore, the γ-PGA could offer a number of cosmetical advantages if its moisturizing effect would be characterized.