Opsin/all-trans-retinal complex activates transducin by different mechanisms than photolyzed rhodopsin

In rhodopsin, the 11-cis-retinal chromophore forms a complex with Lys296 of opsin via a protonated Schiff base. Absorption of light initiates the activation of rhodopsin by cis/trans photoisomerization of retinal. Thermal relaxation through different intermediates leads into the metarhodopsin states which bind and activate transducin (Gt) and rhodopsin kinase (RK). all-trans-Retinal also recombines with opsin independent of light, forming activating species of the receptor. In this study, we examined the mechanism by which all-trans-retinal activates opsin. To exclude other amines except active site Lys296 from formation of Schiff bases, we reductively methylated rhodopsin (PM-rhodopsin), which we then bleached to generate PM-opsin. Using spectroscopic methods and a Gt activation assay, we found that all-trans-retinal interacted with PM-opsin, producing a noncovalent complex that activated Gt. The residual nucleotide exchange in Gt catalyzed by opsin was approximately 1/250 lower relative to that of photoactivated rhodopsin (pH 8.0, 23 degrees C). Addition of equimolar all-trans-retinal led to an occupancy of one-tenth of the putative retinal binding site(s) of opsin and enhanced the Gt activation rate 2-fold. When the concentration of all-trans-retinal was increased to saturation, the Gt activation rate of the opsin/all-trans-retinal complex was approximately 1/33 lower compared to that of photoactivated rhodopsin. We conclude that all-trans-retinal can form a noncovalent complex with opsin that activates Gt by different mechanisms than photolyzed rhodopsin.     

Protection of B lymphocyte hybridoma against starvation-induced apoptosis: survival-signal role of some amino acids

Immunofluorescence microscopic observations indicated that a monoclonal antibody, Vmp 18, raised against the peptide 199-208 of murine interleukin 1 alpha, cross-reacted with an antigenic determinant of Drosophila thorax muscles. Immunoelectron microscopic analysis showed that the gold particles were mainly localized in the Z-line which is the attachment site of thin filaments from adjacent sarcomeres. On the contrary, the antibody failed to mark the Z-line in vertebrate skeletal muscle. A Western blot of total protein extract from Drosophila thorax muscles bound a protein of 43 kDa. Our observations suggest that the Vmp 18 antibody could contribute to clarify the composition of the Z-line in insect's flight muscles.     

The effects of the pretreatment of intravenous high dose methylprednisolone on Na(+)-K(+)/Mg(+2) ATPase and lipid peroxidation and early ultrastructural findings following middle cerebral artery occlusion in the rat

The sodium-potassium activated and magnesium dependent adenosine-5'-triphosphatase (Na(+)-K(+)/Mg(+2) ATPase EC.3.6.1.3.) activity and lipid peroxidation and early ultrastructural findings were determined in rat brain at the acute stage of ischaemia produced by permanent unilateral occlusion of the middle cerebral artery (MCA). The effects of the pretreatment with intravenous high-dose methylprednisolone (MP) on these biochemical indices and ultrastructural findings were also evaluated in the same model. The rats were divided into four groups. In group I, 10 rats were used to determine Na(+)-K(+)/Mg(+2) ATPase activity and the extent of lipid peroxidation by measuring the malondialdehyde (MDA) content and normal ultrastructural findings. In group II on 20 rats, only subtemporal craniectomy was done in order to determine the effects of the surgical procedure on these indices and findings. This group was treated intravenously with saline solution before occlusion. In group III with MCA occlusion, saline solution was administered intravenously to 20 rats in the same amount of methylprednisolone used in group IV, ten minutes before the occlusion. In Group IV, a single high-dose (30 mg/kg) of methylprednisolone was administered intravenously, ten minutes before occlusion in 20 rats. After occlusion of the middle cerebral artery, Na(+)-K(+)/Mg(+2) ATPase activity was decreased promptly in the first ten minutes in the ischaemic hemisphere and remained at a lower level than the contralateral hemispheres in the same group and the normal levels in group I, during 120 minutes of ischaemia. A single dose methylprednisolone pretreatment prohibited the inactivation of Na(+)-K(+)/Mg(+2) ATPase. On the other hand, there was significant difference in malondialdehyde content between group I and group III. Malondialdehyde levels were significantly increased following ischaemia and a non-significant increase was observed in the contralateral hemisphere. Methylprednisolone treatment significantly decreased malondialdehyde content on the side of the ischaemic hemisphere. We conclude that there is a positive relationship between membrane-bound enzyme Na(+)-K(+)/Mg(+2) ATPase activity, malondialdehyde content and early ultrastructural changes in the treated group with MP. These data suggest that the pretreatment injection of high doses (30 mg/kg) methylprednisolone contribute to the protection of the brain from ischaemia with stabilization of the cell membrane by effecting the lipid peroxidation and the activation of Na(+)-K(+)/Mg(+2) ATPase.     

荷能束辐照致使Cu/Ag表面偏析的研究

本文研究了金属(Cu)/金属(Ag衬底)系统的荷能束辐照引起的表面偏析现象。观察到Cu在多晶Ag衬底上溅射淀积过程中,Ag原子在Cu膜表面的偏析,且淀积Cu原子能量越大,Ag原子偏析程度越大,即观察到了淀积Cu原子10~(-1)～1eV量级的平均能量差异对膜层表面偏析行为的影响。对溅射淀积所得膜层进行keV量级的离子束辐照,Ag原子的表面偏析程度更甚。     

提高柴油机缸盖内腔铸造质量的工艺措施

缸盖是柴油机上的重要零件之一。铸造毛坯不可避免地存在劈缝、内腔粘砂、粗糙、局部不通等内腔质量问题 ,从而影响缸盖串水冷却效果。本文介绍了一些工艺措施 ,较好地解决了这个问题。     

自动力套管补贴加固技术及其在B125井的应用

随着油田开发时间的延长，油水井井下套管的损坏将越来越严重，套管故障井将越来越多，为了恢复套损井生产，将套管损坏所造成的损失降到最低，在配套波纹管补贴，水动力补贴，爆炸补贴等专门修套技术的基础上，通过认真调查研究，又配套了操作方便简单，适用套管损坏类型广的自动力套管补贴加固技术，使各种套管变形，套管断错（错开没有位移或位移量不大时）、套管破裂，误射孔井段封堵，已射开水层封堵等修井作业的难度进一步降低，从而进一步提高了修复井综合开发经济效益。     

恢复城市水环境的自然生态

为了确保城市社会经济的可持续发展,城市的水资源管理是重要的一环,而且,这项管理会逐步从防洪、水资源利用的量的管理向水质管理、空间管理和生态体系的保护等综合管理发展,其中恢复河流清澈、优美的自然生态,科学有效地建设城市水环境是个需要研究的大课题.     

液闪效率示踪法校正效果的评价

本文评价了Aloka商品液闪仪效率示踪法dpm校正的效果。轻,中度猝灭校正效果理想,具有简便、实用和适用性广泛的特点。严重化学和颜色猝灭样品的校正结果分别随猝灭增加而向增大和减小的方向偏离,形成喇叭状曲线,文中对这一现象给出初步解释。