Gross N J, Schultz R M
Department of Medicine, Stritch School of Medicine, Loyola University, Chicago, IL.
Biochim Biophys Acta. 1990 May 22;1044(2):222-30. doi: 10.1016/0005-2760(90)90306-i.
Pulmonary surfactant as lavaged from the alveoli exists in at least three structural subtypes, lamellar body-like, tubular myelin and vesicular forms that can be separated on the basis of their buoyant densities. Previous studies have suggested that surfactant is secreted in the lamellar body form and metabolized through the other subtypes in sequence. This metabolic sequence can be reproduced in vitro by cyclic expansion and contraction ('cycling') of the surface area of nascent surfactant at 38 degrees C. Cycling of nascent secretion, which is predominantly of lamellar body-like buoyant density, rapidly converted it to the buoyant density of tubular myelin and then to that of the vesicular subtype. We examined the role of proteinases in the conversion of nascent surfactant subtypes in vitro. Addition of metallo-, cysteine- and acid-proteinase inhibitors to the cycling mix did not inhibit the conversion of tubular myelin to vesicular subtype. However, a variety of serine proteinase inhibitors inhibited the formation of vesicular subtype. Their inhibitory effect was dose-related and most marked for alpha 1-antitrypsin where a concentration equal to that found in the alveolar fluid lining layer resulted in 50% inhibition of the generation of light subtype, suggesting physiological relevance. The enzyme(s) responsible for promoting the generation of light subtype was sedimentable and therefore presumably in particulate form. By differential centrifugation of lung secretions it was separable from alveolar macrophages and partially separable from surfactant itself. It has not been identified, nor has its substrate. We conclude that in vitro cycling provides a model for the study of alveolar surfactant metabolism and that the conversion of tubular myelin to vesicular forms of surfactant requires serine proteinase activity.
从肺泡中灌洗出的肺表面活性物质至少存在三种结构亚型，即板层小体样、管状髓鞘样和囊泡样形式，它们可根据其浮力密度进行分离。先前的研究表明，表面活性物质以板层小体形式分泌，并依次通过其他亚型进行代谢。这种代谢顺序可在体外通过新生表面活性物质在38℃下的表面积循环扩张和收缩（“循环”）来重现。新生分泌物的循环，其主要具有板层小体样浮力密度，迅速将其转化为管状髓鞘样的浮力密度，然后再转化为囊泡亚型的浮力密度。我们研究了蛋白酶在体外新生表面活性物质亚型转化中的作用。向循环混合物中添加金属蛋白酶、半胱氨酸蛋白酶和酸性蛋白酶抑制剂并不能抑制管状髓鞘样向囊泡亚型的转化。然而，多种丝氨酸蛋白酶抑制剂抑制了囊泡亚型的形成。它们的抑制作用与剂量相关，对α1-抗胰蛋白酶最为明显，在肺泡液内衬层中发现的浓度水平可导致轻亚型生成的50%受到抑制，提示其具有生理相关性。负责促进轻亚型生成的酶是可沉淀的，因此可能呈颗粒形式。通过对肺分泌物进行差速离心，它可与肺泡巨噬细胞分离，且部分可与表面活性物质本身分离。该酶尚未被鉴定出来，其底物也未被确定。我们得出结论，体外循环为研究肺泡表面活性物质代谢提供了一个模型，并且管状髓鞘样向囊泡样表面活性物质的转化需要丝氨酸蛋白酶活性。
