Author(s)

Heping Cao^*, Kandan Sethumadhavan, Kanniah Rajasekaran

U.S. Department of Agriculture, Agricultural Research Service, Southern Regional Research Center, New Orleans, LA, USA.

Cotton (Gossypium hirsutum L.) provides a major source of oil for food and feed industries, but little was known about the enzymes in the oil biosynthesis pathway in cottonseed. We are interested in a better understanding of enzymatic components for oil accumulation in cottonseed. The objective of this study was to identify one key enzyme in oil biosynthesis pathway: phosphatidic acid phosphatase (PAP, 3-sn-phosphatidate phosphohydrolase, EC 3.1.3.4). PAP hydrolyzes the phosphomonoester bond in phosphatidate yielding diacylglycerol and Pi. PAPs are generally categorized into Mg²⁺-dependent soluble PAP and Mg²⁺-independent membrane-associated PAP. Cottonseed from 25 - 30 days post anthesis was used for the study. The results showed that an Mg²⁺-independent soluble PAP activity was identified from the cottonseed. While the microsomal fraction of the extract provided only 9% of the PAP activity, 69% of the PAP activity was associated with the cytosol. The PAP activity correlated well with enzyme concentration and incubation time. The pH and temperature optima of the enzyme were pH 5 and 55℃, respectively. Under optimized assay conditions, the V_max and K_m values of cottonseed PAP for dioleoyl phosphatidic acid as the substrate were 2.8 nkat/mg of protein and 539 μM, respectively. Inclusion of the detergent Triton X-100 (0% - 0.5%) or magnesium chloride (1 mM) in the reaction mix did not alter activity to a significant degree. This is the first report of a PAP activity in the seeds of Gossipium hirsutum. This study should provide a basis for purification and characterization of this important enzyme from cottonseed in the future.

Cottonseed, EC 3.1.3.4, Phosphatidate Phosphohydrolase, Phosphatidic Acid Phosphatase, Gossypium hirsutum

Cao, H. , Sethumadhavan, K. and Rajasekaran, K. (2016) Identification of an Mg²⁺-Independent Soluble Phosphatidate Phosphatase in Cottonseed (Gossypium hirsutum L.). Advances in Biological Chemistry, 6, 169-179. doi: 10.4236/abc.2016.66015.