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Characterization of calcium‐independent cytosolic phospholipase A 2 activity in the submucosal regions of rat stomach and small intestine
Author(s) -
Fukushima Takeshi,
Serrero Ginette
Publication year - 1994
Publication title -
lipids
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.601
H-Index - 120
eISSN - 1558-9307
pISSN - 0024-4201
DOI - 10.1007/bf02536724
Subject(s) - cytosol , biochemistry , small intestine , substrate (aquarium) , calcium , enzyme , phospholipase , biology , medicine , chemistry , endocrinology , ecology
Abstract This study was undertaken to compare the calcium‐independent phospholipase A 2 (PLA 2 ) activities in the cytosols of twelve rat tissues and to determine whether their activities were distinct. 1‐ O ‐Alk‐1′‐enyl‐2‐[ 14 C]‐oleoyl‐ sn ‐glycero‐3‐phosphocho‐line (PlsC) and 1‐ O ‐Alk‐1′‐enyl‐2‐[ 14 C]oleoyl‐ sn ‐glycero‐3‐phosphethanolamine (PlsE) were synthesized and used as substrates, instead of phosphatidyl compounds, to exclude hydrolysis by cytosolic PLA 1 activity that could be present in some of the cytosolic preparations. For each tissue, we examined substrate specificity, pH optimum, and effect of adenosine triphosphate (ATP) and ATP analogues. PLA 2 activity was detected in eleven out of the twelve issues examined. Based on substrate specificity and pH optimum, cytosolic calcium‐independent PLA 2 were classified in three groups. The first group, which included PLA 2 from small intestine, stomach and spleen, had the highest specific activity with PlsC as substrate (1253, 309 and 75 nmol/mg protein/hour, respectively) and an optimal pH at 6.5. Activity with PlsE as substrate was much lower (20–37%) than with PlsC. The second group of PLA 2 activities included the cytosolic activities from thymus, lung, liver and pancreas that showed lower specific activities for both substrates (14–23 nmol/mg protein/hour with PlsC) and had a broader optimal pH range of 6.1 to 7.5. The cytosols from brain, kidney, heart and muscle comprised the third PLA 2 group that was found to have a higher specific activity with PlsE (5–20 nmol/mg protein/hour) than PlsC and an optimal pH range from 7.4 to 7.9. Since the highest specific activity was found in the cytosol from small intestine, this PLA 2 was examined further. PLA 2 activity was found to be equally distributed in the cytosol of the submucosal portion of duodenum, jejunum and ileum with an optimal pH of 6.1 and a 5‐fold higher activity with PlsC than PlsE as substrate. Moreover, this PLA 2 activity was inhibited by treatment with detergents. These results indicate the presence in the submucosal portion of the intestine of a calcium‐independent cytosolic PLA 2 with a high specific activity toward PlsC and properties distinct from those described for the PLA 2 found in the intestinal brush‐border.