Phospholipase A2 (PLA2) is an esterase family which catalyzes the hydrolysis of phospholipids at sn-2 ester bonds to yield free fatty acids and lysophospholipids [1,2]. Based on different functions and cellular locations, the PLA2 family is classified to different subclasses, e.g. secretory PLA2 (sPLA2), calcium-independent PLA2 (iPLA2), cytosolic PLA2 (cPLA2), platelet-activating factor-acetylhydrolases (PAF-AHs), adipose-specific PLA2 (AdPLA2), and lysosomal PLA2 [1,3]. Physiologically, the PLA2 family hydrolyzes phospholipids, followed by biochemical processes induced by other enzymes, such as lipoxygenases, cyclooxygenases, and terminal synthases [3]. These biochemical processes produce a series of distinctive phospholipids decomposition products and derivatives [4], which mediate different signaling pathways and cellular reactions through intra- or extra-cellular receptors, and play key roles in the renewal of cell membrane, tissue repair, and immune response [5,6].

PLA2 not only contributes to the metabolism of phospholipids in vivo, endogenous PLA2 in postmortem muscles is still capable of hydrolyzing intramuscular phospholipids [[7], [8], [9]], and exert important impacts on the quality of meat and meat products [[10], [11], [12]]. During manufacturing of meat products, especially those cured meat products, endogenous enzymes including PLA2 may stay active for a long period of time due to the adequate ambient temperature and water activity, and enzymatic activities may be detected even in the end products [11]. Endogenous PLA2 has been found to be connected with declining of intramuscular phospholipids and increasing of free fatty acids in cured meat products [8], and adequate amounts of sodium chloride may stimulate endogenous PLA2 and relative activity of endogenous PLA2 is correlated with formation of flavor compounds [10,11]. During the whole process, physic-chemical factors (such as moisture, content of sodium chloride and sodium nitrite) vary dramatically, which results in variations of endogenous enzymes' activity including PLA2 and affects formation of characteristic flavor [7,11]. It is generally accepted that intramuscular phospholipids are either hydrolyzed by endogenous PLA2 to yield free polyunsaturated fatty acids (PUFAs) followed by oxidation of these free PUFAs, or oxidized to hydroperoxides of phospholipids followed by hydrolysis under the action of endogenous PLA2 [9]. In both paths, hydroperoxides of PUFAs are produced and further decomposed to a series of secondary products, which contribute to the formation of characteristic flavor of meat products. Therefore, degradation of intramuscular phospholipids is regarded as one of the most important biochemical processes during cured meat products' manufacturing, and endogenous PLA2 plays a crucial role in such a biochemical process [10,12].

Quite a lot of studies have been done on endogenous PLA2 in muscles, including variation of activity, relationships with fatty acid composition and flavor of meat products [7,8,11,13]. However, enzymatic properties of endogenous PLA2s in muscles, such as specificity of substrates, impacts of physic-chemical factors, and hydrolysis characteristics of phospholipids and its hydroperoxide, remain largely unknown, due to the difficulty in extraction and purification of endogenous enzymes from animal muscles.

iPLA2s are cytosolic PLA2s that do not require Ca2+ for catalysis, and are designated as group VI PLA2. Among the iPLA2s, those with molecule weight of 80–88 kDa are classified to group VIA PLA2 [14]. VIA PLA2 contains a phospholipase motif proceeded by eight ankyrin repeats, which have been found in hamster, mouse and rat [14] and the identified gene has been found to be expressed in human skeletal muscle [15]. In our previous study, crude enzymes were extracted from pork, beef and chicken muscles, and were found to be able to hydrolyze phosphatidylcholine (PC) and its oxidized forms, and the hydrolysis at sn-2 ester bonds were majorly ascribed to the action by endogenous PLA2 [9]. In order to reveal more information about the endogenous PLA2 in muscles and its role in degradation of intramuscular phospholipids, the catalytic domain of the VIA-2 iPLA2 gene, from porcine skeletal muscle, was cloned, followed by expression via E. coli, and the catalytic domain of pork calcium-independent PLA2 (iPLA2cd) with high enzymatic activity was successfully prepared. Therefore, the objective of the present paper was to carry out a further study on the pork iPLA2cd, including specificity of substrates, impacts of physic-chemical factors and hydrolysis characteristics of PC and its hydroperoxide.