Studies on Triglyceride Hydrolysis in Blood

Recently, from our laboratory, it was suggested that serum nonspecific carboxyl esterase was converted to lipase in the arterial wall. The experiments were carried out to clarify characteristics of esterase and lipase of postheparin plasma. Lipase (triolein hydrolysis) and esterase (tributyrin hydrolysis) activities were increased in blood of rats after heparin injection. Hydrolysis of methylbutyrate by serum esterase was observed to be linearly increased at the lower concentration of methybutyrate than that of 0.153M, but no increase was observed at the higher concentration than that of 0.153M. On the other hand, post heparin plasma, to which phenylmethyl sulfonyl fluoride as an inhibitor of esterase was added, scarecely hydrolysed 0.153M of lower concentration of methylbutyrate, but linearly hydrolysed it at 0.153M to 0.459M of methylbutyrate. These results suggest that lipase acts on hydrophobic condition of methylbutyrate and esterase acts on hydrophilic condition of it as a substrate, because 0.153M methylbutyrate or lower is soluble in water and the higher concentration of methylbutyrate than 0.153M is insoluble in water.Remarkable decrease of lipase activity was observed by trypsin treatment but esterase activity was not. Hydrolysis of 0.153M or lower methylbutyrate as a substrate was unchanted by trypsin treated postheparin lipolytic activity fraction (PHLA-F) compared with nontreated one. But decreased hydrolysis by trypsin-treated PHLA-F was observed when higher concentration than 0.153M of methylbutyrate was used as a substrate.Lipase activity of PHLA-F, which was decreased by trypsin treatment, was recovered when serum was added. Above these results suggest that trypsin treatment or serum might modify the hydrophobicity of PHLA-F.1) Kohji Shirai, Nobuo Matsuoka, Yasushi Saito, Akira Kumagai, Toshiharu Muraoka, Hiromichi Okuda: Hyperlipidimia and Atherosclerosis., J. Jap. Atheroscler. Soc. 6 509 (1978):