Phospholipase A1, A2 and
lysophospholipase activities in microsomes of
Novikoff hepatoma host rat liver and regenerating rat liver were compared using 1-[9', 10'-3H2]palmitoyl-2-[1'-14C] linoleoyl-sn-glycero-3-phosphoethanolamine, 1-[1' -3H-]hexadecyl-2-acyl-sn-glycero-3-
phosphoethanolamine, and 1-[9', 10'-3H2]palmitoyl-sn-glycero-3-
phosphoethanolamine as substrates. 1. Microsomes of all three tissues showed two pH dependent peaks of hydrolytic activity, one at pH 7.5 and another at pH 9.5. 2.
Phospholipid hydrolytic activity in microsomes from host liver and regenerating liver require Ca2+ for hydrolysis at pH 9.5, but not at pH 7.5.
Hepatoma microsomes require Ca2+ for activity at both pH values. 3.
Phospholipase A1 activity, stimulated by addition of
Triton X-100 to the incubation mixtures, was detected in both host liver and regenerating liver microsomes. There was no evidence of
phospholipase A1 activity in
hepatoma microsomes. 4.
Phospholipase A2 was detected in microsomes of all three tissues using 1-[1'-3H] hexadecyl-2-acyl-sn-glycero-3-phosphoethanolamine as a substrate. The activity required
calcium and was inhibited by
Triton X-100. 5.
Lysophospholipase activity was evident in the microsomes from all three tissues. The activity was inhibited by both Ca2+ and
Triton X-100. 6. Differences were also detected between host liver and
hepatoma microsomal
phospholipid hydrolase activities with respect to the effect of increasing
protein concentration, apparent Michaelis-Menten constants, and time course of the reaction.