Svehag S E, Bloth B, Seligmann M
J Exp Med. 1969 Oct 1;130(4):691-705. doi: 10.1084/jem.130.4.691.
The ultrastructure of papain and pepsin-digested products of human IgM globulins has been analyzed. Papain digestion was performed both in the presence and absence of cysteine. The Fcmicro fragment was found to represent the central ring structure in the intact IgM molecule, plus a minor part of the appendages extending from the ring. The Fcmicro ring structure was occasionally seen to be composed of dimers of short rods, probably identical with the endpieces of two micro-chains. Such dimeric structures, released from the intact Fcmicro rings, had a tendency to aggregate sidewise, producing complexes of varying size. The dimensions of the Fcmicro fragments were: outer diameter approximately 85 A, inner diameter about 40 A. The length of the protrusions varied from 20-30 A. The Fabmicro preparations contained long strands of sidewise aggregated, short rod-shaped fragments. No aggregates were seen in the F(ab'')(2)micro preparations. The two Fab''micro units in the dimeric F(ab'')(2)micro fragments were usually parallel to each other. The dimensions of the Fabmicro and F(ab'')(2)micro fragments were 50-80 A x 30 A and 75-80 A x 55 A, respectively. These findings provide morphological evidence that the C-terminal ends of the micro-chains (the Fcmicro fragment) make up the central ring structure in the IgM molecule. They further indicate that the F(ab'')(2)micro fragments constitute about (3/4) of the appendages extending from this ring structure.
已对人IgM球蛋白的木瓜蛋白酶和胃蛋白酶消化产物的超微结构进行了分析。木瓜蛋白酶消化在有和没有半胱氨酸的情况下都进行了。发现Fcmicro片段代表完整IgM分子中的中央环结构，以及从环延伸的附属物的一小部分。偶尔可以看到Fcmicro环结构由短棒的二聚体组成，可能与两条微链的末端相同。从完整的Fcmicro环释放的这种二聚体结构有侧向聚集的趋势，产生大小不同的复合物。Fcmicro片段的尺寸为：外径约85埃，内径约40埃。突出物的长度在20 - 30埃之间变化。Fabmicro制剂包含侧向聚集的长链短棒状片段。在F(ab'')(2)micro制剂中未观察到聚集物。二聚体F(ab'')(2)micro片段中的两个Fab''micro单元通常相互平行。Fabmicro和F(ab'')(2)micro片段的尺寸分别为50 - 80埃×30埃和75 - 80埃×55埃。这些发现提供了形态学证据，表明微链的C末端（Fcmicro片段）构成了IgM分子中的中央环结构。它们进一步表明，F(ab'')(2)micro片段约占从该环结构延伸的附属物的(3/4)。
