Tilney L G
J Cell Biol. 1975 Feb;64(2):289-310. doi: 10.1083/jcb.64.2.289.
When Limulus sperm are induced to undergo the acrosomal reaction, a process, 50 mum in length, is generated in a few seconds. This process rotates as it elongates; thus the acrosomal process literally screws through the jelly of the egg. Within the process is a bundle of filaments which before induction are coiled up inside the sperm. The filament bundle exists in three stable states in the sperm. One of the states can be isolated in pure form. It is composed of only three proteins whose molecular weights (mol wt) are 43,000, 55,000, and 95,000. The 43,000 mol wt protein is actin, based on its molecular weight, net charge, morphology, G-F transformation, and heavy meromyosin (HMM) binding. The 55,000 mol wt protein is in equimolar ratio to actin and is not tubulin, binds tenaciously to actin, and inhibits HMM binding. Evidence is presented that both the 55,000 mol wt protein and the 95,000 mol wt protein (possibly alpha-actinin) are also present in Limulus muscle. Presumably these proteins function in the sperm in holding the actin filaments together. Before the acrosomal reaction, the actin filaments are twisted over one another in a supercoil; when the reaction is completed, the filaments lie parallel to each other and form an actin paracrystal. This change in their packing appears to give rise to the motion of the acrosomal process and is under the control of the 55,000 mol wt protein and the 95,000 mol wt protein.
当鲎精子被诱导发生顶体反应时，会在几秒钟内产生一个长50微米的过程。这个过程在伸长时会旋转；因此顶体过程实际上是像螺丝一样穿过卵的胶状物。在这个过程中有一束细丝，在诱导之前它们盘绕在精子内部。细丝束在精子中存在三种稳定状态。其中一种状态可以以纯形式分离出来。它仅由三种蛋白质组成，其分子量分别为43,000、55,000和95,000。基于其分子量、净电荷、形态、G-F转化和重酶解肌球蛋白（HMM）结合，分子量为43,000的蛋白质是肌动蛋白。分子量为55,000的蛋白质与肌动蛋白等摩尔比，不是微管蛋白，与肌动蛋白紧密结合，并抑制HMM结合。有证据表明，分子量为55,000的蛋白质和分子量为95,000的蛋白质（可能是α-辅肌动蛋白）也存在于鲎的肌肉中。推测这些蛋白质在精子中起到将肌动蛋白丝聚集在一起的作用。在顶体反应之前，肌动蛋白丝相互缠绕形成超螺旋；当反应完成时，这些丝彼此平行排列并形成肌动蛋白副晶体。它们堆积方式的这种变化似乎导致了顶体过程的运动，并且受分子量为55,000的蛋白质和分子量为95,000的蛋白质的控制。
