Diacylglycerol kinase (DGK) phosphorylates diacylglycerol (DG) to produce 
phosphatidic acid (PA). Mammalian DGK comprises ten isozymes (α-κ) and regulates 
a wide variety of physiological and pathological events, such as cancer, type II 
diabetes, neuronal disorders and immune responses. DG and PA consist of various 
molecular species that have different acyl chains at the sn-1 and sn-2 
positions, and consequently, mammalian cells contain at least 50 structurally 
distinct DG/PA species. Because DGK is one of the components of 
phosphatidylinositol (PI) turnover, the generally accepted dogma is that all DGK 
isozymes utilize 18:0/20:4-DG derived from PI turnover. We recently established 
a specific liquid chromatography-mass spectrometry method to analyze which PA 
species were generated by DGK isozymes in a cell stimulation-dependent manner. 
Interestingly, we determined that DGKδ, which is closely related to the 
pathogenesis of type II diabetes, preferentially utilized 14:0/16:0-, 
14:0/16:1-, 16:0/16:0-, 16:0/16:1-, 16:0/18:0- and 16:0/18:1-DG species 
(X:Y = the total number of carbon atoms: the total number of double bonds) 
supplied from the phosphatidylcholine-specific phospholipase C pathway, but not 
18:0/20:4-DG, in high glucose-stimulated C2C12 myoblasts. Moreover, DGKα mainly 
consumed 14:0/16:0-, 16:0/18:1-, 18:0/18:1- and 18:1/18:1-DG species during cell 
proliferation in AKI melanoma cells. Furthermore, we found that 16:0/16:0-PA was 
specifically produced by DGKζ in Neuro-2a cells during retinoic acid- and serum 
starvation-induced neuronal differentiation. These results indicate that DGK 
isozymes utilize a variety of DG molecular species derived from PI 
turnover-independent pathways as substrates in different stimuli and cells. DGK 
isozymes phosphorylate various DG species to generate various PA species. It was 
revealed that the modes of activation of conventional and novel protein kinase 
isoforms by DG molecular species varied considerably. However, PA 
species-selective binding proteins have not been found to date. Therefore, we 
next attempted to identify PA species-selective binding proteins from the mouse 
brain and identified α-synuclein, which has causal links to Parkinson's disease. 
Intriguingly, we determined that among phospholipids, including several PA 
species (16:0/16:0-PA, 16:0/18:1-PA, 18:1/18:1-PA, 18:0/18:0-PA and 
18:0/20:4-PA); 18:1/18:1-PA was the most strongly bound PA to α-synuclein. 
Moreover, 18:1/18:1-PA strongly enhanced secondary structural changes from the 
random coil form to the α-helix form and generated a multimeric and proteinase 
K-resistant α-synuclein protein. In contrast with the dogma described above, our 
recent studies strongly suggest that PI turnover-derived DG species and also 
various DG species derived from PI turnover-independent pathways are utilized by 
DGK isozymes. DG species supplied from distinct pathways may be utilized by DGK 
isozymes based on different stimuli present in different types of cells, and 
individual PA molecular species would have specific targets and exert their own 
physiological functions.