Tojo H, Ying Z, Okamoto M
Department of Molecular Physiological Chemistry, Osaka University Medical School, Japan.
Eur J Biochem. 1993 Jul 1;215(1):81-90. doi: 10.1111/j.1432-1033.1993.tb18009.x.
Guinea pig gastric mucosa and juice contained exceptionally high phospholipase-A2 activity, whereas the activity in the pancreas was only minimal. Phospholipases A2 were purified to homogeneity from these three tissues. Structural evidence, including the sequence of the NH2-terminal 41 residues, the amino-acid composition and the molecular mass (13902 +/- 3 Da) determined accurately by mass spectrometry, showed that the gastric mucosa enzyme belongs to the pancreatic type. An unique feature of the sequence is the substitution of Phe for the hitherto invariant Tyr28 in the calcium-binding loop of pancreatic phospholipases A2. The affinity of the guinea pig enzyme for Ca2+ in the presence of substrate was, however, identical to that of the rat enzyme with Tyr28, suggesting the interaction of a phenolic hydroxyl group of the Tyr with its neighboring residues is not significantly linked to the binding of Ca2+. The NH2-terminal sequences and immunochemical properties of the enzymes purified from the gastric juice and pancreas were identical to those of the gastric mucosa enzyme. The distribution of cells immunoreactive with anti-(gastric PLA2) immunoglobulin in the stomach was quite similar to that of the chief cells. Unlike in pancreas of other animals, the prophospholipase A2 was not detectable in gastric mucosa or juice homogenates treated with diisopropyl fluorophosphate or in column effluents during purification under acidic conditions. An appreciable prophospholipase-A2-activating activity was not detectable in gastric mucosa extracts at low pH relevant to gastric juice, using rat prophospholipase A2 as substrate. This opposes the activation of secreted proenzyme in the gastric juice.
豚鼠胃黏膜和胃液中含有异常高的磷脂酶A2活性，而胰腺中的活性则极低。从这三种组织中纯化得到了均一的磷脂酶A2。包括氨基末端41个残基的序列、氨基酸组成以及通过质谱准确测定的分子量（13902±3 Da）等结构证据表明，胃黏膜酶属于胰腺型。该序列的一个独特特征是，在胰腺磷脂酶A2的钙结合环中，苯丙氨酸取代了迄今不变的酪氨酸28。然而，在有底物存在的情况下，豚鼠酶对Ca2+的亲和力与具有酪氨酸28的大鼠酶相同，这表明酪氨酸的酚羟基与其相邻残基的相互作用与Ca2+的结合没有显著联系。从胃液和胰腺中纯化得到的酶的氨基末端序列和免疫化学性质与胃黏膜酶相同。胃中与抗（胃磷脂酶A2）免疫球蛋白反应的细胞分布与主细胞的分布非常相似。与其他动物的胰腺不同，在用氟磷酸二异丙酯处理的胃黏膜或胃液匀浆中，或在酸性条件下纯化过程中的柱流出物中，均未检测到前磷脂酶A2。以大鼠前磷脂酶A2为底物，在与胃液相关的低pH值下，胃黏膜提取物中未检测到明显的前磷脂酶A2激活活性。这与胃液中分泌的酶原的激活情况相反。
