Harrington W F, Karr T, Busa W B
Johns Hopkins University, Department of Biology, Baltimore, MD 21218.
Adv Exp Med Biol. 1993;332:603-12; discussion 612-3. doi: 10.1007/978-1-4615-2872-2_54.
When rabbit psoas myofibrils in rigor are cross-linked with DMS (dimethyl suberimidate) for various periods of time, they contract on activation to a final sarcomere spacing of 1.3-1.5 microns. This behavior is observed out to 100 min cross-linking time (2 mg/ml DMS; 10 degrees C). Over the next 100 min of cross-linking, the sarcomere spacing, following activation and contraction, gradually increases and finally plateaus near its initial (rigor) value. We also determined the unloaded shortening velocity of the cross-linked myofibrils using an inverted microscope equipped with a video camera. Following photo-activation of caged ATP, the fast contracting process observed in control (untreated) myofibrils decreases in rate and magnitude with increasing cross-linking time. When taken together with earlier cross-linking studies, our present results suggest that the suppression of contraction may result from two distinct cross-linking reactions: (1) Cross-linking of myosin rods in the filament core which immobilizes the S-2 subunit and acts to decrease the isometric force (approximately 90% at 100 min). (2) Cross-linking within the S-1 subunit. This latter reaction is believed to account for the continuous decay in the rate and magnitude of the unloaded shortening process.
当处于僵直状态的兔腰大肌肌原纤维与亚胺二甲酯（DMS）交联不同时间后，它们在激活时会收缩至最终肌节间距为1.3 - 1.5微米。在长达100分钟的交联时间内（2毫克/毫升DMS；10摄氏度）都能观察到这种行为。在接下来100分钟的交联过程中，激活和收缩后的肌节间距逐渐增加，最终稳定在接近其初始（僵直）值的水平。我们还使用配备摄像机的倒置显微镜测定了交联肌原纤维的无负荷缩短速度。在笼形ATP光激活后，对照（未处理）肌原纤维中观察到的快速收缩过程，其速率和幅度会随着交联时间的增加而降低。结合早期的交联研究，我们目前的结果表明，收缩的抑制可能源于两种不同的交联反应：（1）细丝核心中肌球蛋白杆的交联，这会固定S - 2亚基并降低等长力（在100分钟时约降低90%）。（2）S - 1亚基内的交联。据信后一种反应是无负荷缩短过程的速率和幅度持续衰减的原因。
