Biology Reference
In-Depth Information
phosphate
O
pKa 12.8
HO
OH
pKa 7.2
P
OH
pKa 2.1
O
P
O
O
O
-
pKa 2.1
FIGURE 5.9
pKas of dissociable groups on phosphate.
phospholipids, PA comprises part of the membrane lipid bilayer and contributes to the
membrane's physical properties. At physiological pH, PA has a net charge of ~
1.5
and so is a strong anion that contributes negative charge density to the membrane. PA
has a unique shape, possessing a small highly-charged head group whose charge lies
very close to the glycerol backbone. PA's shape is probably related to its significant role
in membrane vesicle fission and fusion events. Membrane PAs can be aggregated by
Ca
2
รพ
, resulting in the formation of PA-rich microdomains that are highly sensitive to
pH, temperature and cation concentration. PA also induces negative curvature stress on
adjacent proteins, affecting their activity. The activity of more than 10 proteins including
PKC and PLC have been shown to be altered by PA (for example,
[11]
).
PA is a vital cell lipid that is maintained at extremely low levels in the cell by the activity of
potent LPPs (lipid phosphate phosphohydrolases). LPPs rapidly convert PA to DAG (diacyl
glycerol), a metabolic precursor for many lipids. PA has emerged as a new class of lipid medi-
ators involved in diverse cellular functions in plants, animals, and microorganisms
[12]
.
O
pKa 7.2
O
OH
P
O
-
pKa 2.1
FIGURE 5.10
PA
e
Phosphatidic acid.
