Phospholipase A2 is associated with albumin in patients with acute pancreatitis

Evidence for the association of serum phospholipase A2 (PLA2) (EC 3.1.1.4) and serum proteins was examined. The effect of this on the PLA2 results from patients diagnosed as having acute pancreatitis was investigated. Two distinct zones of PLA2 activity were found on agarose electrophoresis of purified human PLA2 in the presence of albumin, and in the sera from the acute pancreatitis patients. One of the zones was coincident with albumin. To investigate this finding, a comparison of the PLA2 activity in sera and protein-free ultrafiltrates prepared from the sera of the same patients, showed that PLA2 was not completely ultrafiltered as would be expected from its molecular weight. The PLA2 method used employed a radiolabelled E. coli membrane-phospholipid substrate. It has been previously shown that there is an association between PLA2 and albumin and there is good evidence that albumin interferes with certain methods used for the measurement of PLA2. The recovery of PLA2 activity from the ultrafiltrates of patients' serum was highly variable and it may be that serum proteins, in particular albumin, provide a protective 'buffer' against small increases in PLA2 activity. Inhibitor proteins such as lipocortin which were originally postulated as binding to the enzyme, have been subsequently shown to be substrate-binding agents. However, direct protein effects may be a factor in the inconsistent PLA2 results reported in studies of patients with acute pancreatic disease.