Biomedical subjects

W Dierick

Publications and source records attributed to W Dierick.

At least 55 records · Page 3Linked to original sources

PubMed1978

Acid triacylglycerol lipase from bovine thyroid gland.

An acid lipase has been detected in bovine thyroid tissue using triolein as a substrate. The activity, probably associated with the lysosomes, displays a rather broad pH-optimum in the pH 4 to pH 6.5 range. The lipase activity can be partially purified by cosedimentation with lysosomes followed by solubilization through detergent and chromatography on Sephadex G-200 and carboxymethyl cellulose. The elution profile on Sephadex G-200 shows one peak (moleculare weight 67,000 +/- 2,000). In the final CM-cellulose step, two lipase peaks (lipase LA and lipase LB) are found. Sulhydryl reagents (iodoacetate, iodoacetamide, and N-ethylmaleimide) as well as mercuric ions markedly reduce both enzyme activities. Calcium ions, EDTA, and heparin have no effect. Sodium fluoride and diisopropylfluorophosphate are only slightly inhibitory. Sodium chloride causes a slight increase in both lipase activities. Anionic phospholipids such as cardiolipin and phosphatidylserine are not essential for enzyme activity.

Animals↗

PubMed1978

Lipolytic enzymes in bovine thyroid tissue. I. Subcellular localization, purification and characterization of acid phospholipase A1.

In mammalian cells the catabolism of membrane phosphoglycerides proceeds probably entirely through a deacylation pathway catalysed by phospholipase A and lysophospholipase (Wise & Elwyn, 1965). In the initial attack of diacylphosphoglycerides by phospholipase A two enzymatic activities with different positional specificities have been distinguished: phospholipase A1 (phosphatidate 1-acyl hydrolase EN 3.1.1.32) and phospholipase A2 (phosphatidate 2-acyl hydrolase EN 3.1.1.4) (Van Deenen & De Haas, 1966). Studies on these intracellular phospholipases were mainly concerned with their subcellular localization. Only occasionally more detailed enzymatic investigations have been conducted on them, in contrast to export phospholipases e.g. from snake venom, bee venom and porcine pancreas, which have been extensively investigated (Brockerhoff & Jensen 1974a). In a previous paper (De Wolf et al., 1976a), the presence of phospholipase A1 and phospholipase A2 activities in bovine thyroid was demonstrated, using 1-[9, 10-3H] stearoyl-2-[1-14C] linoleyl-sn-glycero-3-phosphocholine as a substrate. Optimal activity was observed in both instances at pH 4. Addition of the anionic detergent sodium taurocholate increased the A2 type activity and decreased the A1 type activity suggesting the presence of different enzymes. The lack of influence of Ca2+-ions and EDTA and the acid pH optima could suggest lysosomal localization. In this paper the subcellular distribution of both acid phospholipase activities is described as well as a purification scheme for phospholipase A1. Some characteristics of the purified enzyme preparation are discussed.

Animals↗

PubMed1978

Lipolytic enzymes in bovine thyroid tissue. II. Hydrolysis of [3H, 14C] phosphatidylethanolamine by neutral and alkaline phospholipase A activities.

Phospholipase and lysophospholipase activities are present in bovine thyroid (De Wolf et al., 1976). However, using exogenous [14C] phosphatidylcholine as substrate and subcellular fractions as enzyme source no activity could be detected at neutral and alkaline pH. Phospholipase A2 activity was found at neutral pH when [14C] phosphatidylethanolamine was substituted for [14C] phosphatidylcholine (De Wolf et al., 1976). In the present paper the occurrence of neutral and alkaline phospholipase A activities is clearly established. In addition their subcellular localization was investigated.

Animals↗

PubMed1978