Substrate specificity of MPlaG. The chain length selectivities of MPlaG toward triglycerides (A), p-nitrophenyl esters (B), and phosphatidylcholine (C) were determined by using pH titration, spectrophotometry, and LC-MS, respectively. In panels A and B, the vertical and horizontal axes indicate substrate carbon chain lengths and relative activities (with a maximum value of 100%), respectively. (C) For LC-MS analysis, reaction products obtained from reaction of MPlaG with phosphatidylcholine substrates were separated by HPLC at the indicated retention times: for diC6PC, 8.77 min (m/z 498 of 1,2-dihexanoyl-phosphatidylcholine; 89.6%) and 10.36 min (m/z 400 of 2-hexanoyl-lysophosphatidylcholine; 10.4%); for diC7PC, 8.40 min (m/z 526 of 1,2-diheptanoyl-phosphatidylcholine; 50.5%) and 9.99 min (m/z 414 of 2-heptanoyl-lysophosphatidylcholine; 49.5%); for diC8PC, 8.14 min (m/z 554 of 1,2-dioctanoyl-phosphatidylcholine; 49.6%) and 9.73 min (m/z 428 of 2-octanoyl-lysophosphatidylcholine; 50.4%); and for diC14PC, 7.68 min (m/z 722 of 1,2-dimyristoyl-phosphatidylcholine; 96.5%) and 8.91 min (m/z 512 of 2-myristoyl-lysophosphatidylcholine; 3.5%).