THE DIFFERENTIATION OF PHOSPHOLIPASE A₁ AND A₂ IN RAT AND HUMAN NERVOUS TISSUES

Abstract

—Lipid‐free extracts of rat and human brain have been prepared and shown to contain phospholipase A1 and A2 activities and a lysophospholipase. The phospholipase Aj activity has pH optima of 4·2 and 4·6 in rat and human brain, respectively; it can be partially purified and isolated in high yields by dialysing the extracts at low pH. The purified preparations hydrolyse the ester bond at the 1‐position in lecithin, phosphatidyl‐ethanolamine and phosphatidylserine, but have little or no action on triglyceride or cholesterol ester. An assay system for the enzyme is described. Phospholipase A2 activity is optimal at pH 5·5 in rat brain extracts and at pH 5·0 in extracts of human brain. The phospholipase A2 activity of human cerebral cortex is largely unaffected by heating extracts at 70°C for 5 min, whereas this treatment substantially inactivates phospholipase A1 and completely destroys lysophospholipase. Phospholipase A1 is widely distributed in both grey and white matter of human brain and is also present in peripheral nerve. Phospholipase A2 activity is lower than A1 in all regions of the CNS examined so far, and is absent from peripheral nerve. Neither enzyme appears to require Ca2+ but both are inhibited by di‐isopropylfluorophosphate (DFP, 2 × 10−6 m) and thus differ from phospholipase A of pancreas. These studies confirm that the phospholipase A1 and A2 activities in brain are due to separate enzymes.

Cell Damage in the Brain: A Speculative Synthesis

“…Let us recall that direct evidence exists for entry of Ca2+ into cells during ischemia and status epilepticus (see above); in all probability, massive influx of Ca2+ also occurs in hypoglycemia. Furthermore, brain tissues contain appreciable activities of phos pholipase AI and A2 (e .g., Cooper and Webster, 1970;Bazan, 1971;Woelk and Porcellati, 1973), and although their Ca2+ dependence may not have been clearly documented, the evidence derived fr om other tissues is overwhelming (see Derksen and Cohen, 1975;Knapp et aI ., 1977;Borgeat and Samuelsson, 1979) . Thus, it seems permissible to use the increase in FF A as an indicator of a rise in intracellular free CaH activity .…”

Choline and phospholipid metabolism and the synthesis of acetylcholine in rat brain

“…Several investigations have indicated that phosphatidylcholine and lysophosphatidylcholine can enter the brain intact [Illingworth and Portman, 1972a;LcKim et al, 1972;Orlando et al, 19751. The brain contains both phospholipase D and lysophospholipase D, which catalyze the direct release of Ch from phosphatidylcholine and lysophosphatidylcholine, respectively, as well as enzymes that catalyze the stepwise degradation of phospholipids and enzymes that are capable of releasing lipid-bound Ch by the base exchange reaction [Cooper and Webster, 1970;Ansell and Spanner, 1971b;Illingworth and Portman, 1973;Woelk et al, 1974;Wykle and Schremmer, 1974;Saito and Kanfer, 19751. brain tissue in vitro was first demonstrated by Bhatnagar and MacIntosh [1967] and has since been confirmcd by other investigators [Freeman and Jenden, 19761. Dross and Kewitz [ 19721 first showed the in vivo release of Ch when they reported an anteriovenous concentration difference of Ch of 7 nmole ml-' between the femoral arterial and jugular veins of the rat.…”

Purification and Some Properties of Membrane-Associated Phospholipase A(2) of Human Spleen

“…Gabexate mesilate, chlorproma zine and p-bromophenacyl bromide inhib ited the enzyme activity, but the enzyme was not inhibited by cytidine diphosphate cho line at the concentration of 5 mmol/1. vous tissues [25], rat lung [26], mouse mam mary gland [27], human gallbladder epithe lium [28], human amniotic fluid [29], human polymorphonuclear leukocytes [30], rabbit inflammatory exudates [31], bovine thyroid [32], human red cells [33], rat testis [34], mouse sperm [35] and human rheumatoid fluids [36]. But, only a few reports have appeared on the purification and the proper ties of the enzymes, because the specific ac tivity and the content of the enzymes are very low.…”