Determining normal bolus size for thin liquids

In order to define a suitable volume of barium to be delivered to patients during the radiographic evaluation of pharyngoesophageal function during swallowing, three different age groups of nondysphagic volunteers were studied. Subjects randomly swallowed boluses of water, barium, and Coca-Cola. The size of a normal thin liquid bolus was 21 ml (SD±5 ml). We intend to include this information to compare different bolus sizes in cineradiographic examination of patients with swallowing complaints.     

Role and pitfalls of hepatic helical multi-phase CT scanning in differential diagnosis of small hemangioma and small hepatocellular carcinoma

AIM To compare and analyze the contrast enhancement appearance of small hemangioma (SHHE) and small hepatocellular carcinoma (SHCC) with helical multi-phase CT scanning so as to determine their roles and pitfalls in the differential diagnosis of SHHE and SHCC.METHODS The pre and postcontrast CT scanning of the liver in 73 cases (38 SHHE, 35 SHCC) were carried out. The first phase scan of the entire liver began at 30s after the injection of contrast medium, the second and third phases began at 70s, and 4min respectively. The contrast enhancement patterns and characteristics of all lesions were observed and compared.RESULTS In SHHE, 64.29% (27/42) had typical manifestations in two-phase dynamic scanning, such as peripheral dramatic high-density enhancement of the lesions with progressive opacification from the periphery toward the center, 30.95% (13/42) were hyperdense in both phases and 4.76% (2/42) were hypodense in both phases. In the third phase scanning, 96.67% (28/30) of SHHE were hyperdense and isodense. In SHCC 59.52% (25/42) presented typical appearances, such as hyperdense in the first phase and hypodense in the second phase, 23.81% (10/42) were hyperdense in the first phase and isodense in the second phase with 4.76% (2/42) of hypodense in both phases. In the third phase scanning, 85.71% (24/28) of SHCC were hypodense.CONCLUSION According to the contrast enhancement patterns of SHHE and SHCC in the two-phase or multi-phase scanning by helical CT, diagnosis can be established in the majority of lesions, while some atypical cases needed MRI for further investigation.     

Structure of NDP-forming Acetyl-CoA synthetase ACD1 reveals a large rearrangement for phosphoryl transfer

The NDP-forming acyl-CoA synthetases (ACDs) catalyze the conversion of various CoA thioesters to the corresponding acids, conserving their chemical energy in form of ATP. The ACDs are the major energy-conserving enzymes in sugar and peptide fermentation of hyperthermophilic archaea. They are considered to be primordial enzymes of ATP synthesis in the early evolution of life. We present the first crystal structures, to our knowledge, of an ACD from the hyperthermophilic archaeon Candidatus Korachaeum cryptofilum. These structures reveal a unique arrangement of the ACD subunits alpha and beta within an α₂β₂-heterotetrameric complex. This arrangement significantly differs from other members of the superfamily. To transmit an activated phosphoryl moiety from the Ac-CoA binding site (within the alpha subunit) to the NDP-binding site (within the beta subunit), a distance of 51 Å has to be bridged. This transmission requires a larger rearrangement within the protein complex involving a 21-aa-long phosphohistidine-containing segment of the alpha subunit. Spatial restraints of the interaction of this segment with the beta subunit explain the necessity for a second highly conserved His residue within the beta subunit. The data support the proposed four-step reaction mechanism of ACDs, coupling acyl-CoA thioesters with ATP synthesis. Furthermore, the determined crystal structure of the complex with bound Ac-CoA allows first insight, to our knowledge, into the determinants for acyl-CoA substrate specificity. The composition and size of loops protruding into the binding pocket of acyl-CoA are determined by the individual arrangement of the characteristic subdomains.NDP-forming acyl-CoA synthetases (ACDs) catalyze the conversion of acyl-CoA thioesters to the corresponding acids and couple this reaction with the synthesis of ATP via the mechanism of substrate-level phosphorylation. ACDs have been studied in detail in hyperthermophilic archaea, where they function as the major energy-conserving enzymes in the course of anaerobic sugar and peptide fermentation (1–4). It is believed that ACDs represent a primordial mechanism of ATP synthesis in the early evolution of life. ACDs were found in all acetate (acid)-forming archaea (5, 6) and in the eukaryotic parasitic protists Entamoeba histolytica (7) and Giardia lamblia (8), but they have not been found in acetate-forming bacteria. In bacteria, with the exception of Chloroflexus (9), the conversion of inorganic phosphate and the thioester acetyl (Ac)-CoA to acetate and ATP is catalyzed by two enzymes, phosphate Ac-transferase and acetate kinase (10). Following the identification of ACD genes (5, 11) a novel protein superfamily of NDP-forming ACDs was proposed by a bioinformatics analysis (8). In addition to ACDs, this superfamily contains the well-characterized succinyl-CoA synthetases (SCSs) and ATP-citrate lyases (ACLYs) (8). Each ACD is composed of at least five subdomains with variable sequential arrangement (8). This phenomenon, termed “domain shuffling,” is one of the key features of this superfamily (8). Superposition of several structures of SCS from Escherichia coli (ecSCS) (12–14), Thermus aquaticus (15), the mammalian GTP-specific SCS from pig (16), and a truncated form of human ACLY (17, 18) revealed that subdomains 1–5 share a common arrangement in these enzymes. From detailed studies of the reaction mechanism of ecSCS, a crucial enzyme tightly connected to the TCA cycle, a three-step mechanism was proposed, which involves the phosphorylation of a highly conserved His residue at the first active site (site I) as an intermediate step (12, 13). Subsequently, the phosphoryl moiety is transferred onto an NDP that is bound at the second active site (site II). The distance of around 36 Å between site I and site II is assumed to be bridged by a so-called “swinging loop” (12, 14, 19). A mechanism comparable to the mechanism of the SCSs was presumed for the ACDs (20). A study based on sequence, biochemical, and mutational analyses identified a highly conserved and functional relevant His residue within the beta subunit of the ACDs (20). Of note, the SCS enzymes do not contain a comparable His residue. Thus, an extension of the mechanism by a fourth step was suggested for the ACD1 from Pyrococcus furiosus (20). Here, the second His residue is thought to serve as an additional intermediate, which gets phosphorylated transiently during the enzymatic reaction and subsequently transmits the phosphoryl moiety onto the bound NDP. The necessity for a four-step mechanism may originate from a shortening of the proposed swinging loop, which facilitates the phosphoryl transfer between the subunits (20). However, due to the completely different arrangement of the subdomains within ACD [alpha(1-2-5)/beta(3-4)] in comparison to ecSCS [alpha(1-2)/beta(3-4-5)], a different 3D arrangement of the subdomains in ACD and, as a consequence, a variation of the proposed reaction steps has to be considered.ACDs are versatile enzymes that are capable of metabolizing a variety of CoA thioesters generated in the course of sugar and peptide fermentation (3, 4, 21). In contrast, the ecSCS specifically binds succinyl-CoA, accepting only small aliphatic CoA thioesters as additional substrates (22). The ACLY is even more specific for Ac-CoA (23). Because ACDs are involved in sugar and amino acid metabolism, they are ambivalent regarding their converted substrates (3, 4, 24, 25). In addition, domain shuffling creates a very diverse pattern of subdomain organization within members of the ACD family (8). Some ACD enzymes are even built up as single-chain proteins with fused alpha-beta or beta-alpha subunits. The linker region between the fused subunits is usually very short (8). Therefore, a structural model for ACDs based on the structure of ecSCS as presented by Bräsen et al. (20) cannot be fully compatible with those single-chain ACDs, because distances of more than 60 Å between the termini of individual alpha and beta subunits must be bridged.So far, there are no structural data to explain these described peculiarities (necessity of a second His, different arrangement of the subdomains, and broader substrate selectivity). In this study, we present a comprehensive analysis of various crystal structures of the functional complex of the ACD isoform 1 from the hyperthermophilic archaeon Candidatus Korarchaeum cryptofilum (ckcACD1). Ca. K. cryptofilum belongs to the most ancestral archaea (26). Based on genome analyses, Ca. K. cryptofilum has been proposed to ferment amino acids using ACDs as major energy-conserving enzymes (26). Three ACD isoenzymes with different substrate specificities have been characterized (27). ckcACD1 converts small aliphatic CoA thioesters. It is composed of four protein chains (two alpha subunits and two beta subunits) that form an α₂β₂-heterotetramer. Each alpha subunit has one active site for acyl-CoA binding, and each beta subunit has one active site for NDP binding. Due to its similar molecular composition and kinetic properties as ACD1 from the hyperthermophilic archaeon P. furiosus (pfACD1), it is likely that ckcACD1 follows the same four-step catalytic reaction mechanism as has been proposed for the homologous pfACD1 (20). In particular, the structural rearrangements accompanying the phosphate shuttle process between alpha and beta subunits of ACD will be described for the first time to our knowledge. This work provides direct evidence for the proposed loop swinging, which, in addition, can explain the necessity for a second active-site His located in the beta subunit near site II. Further detailed analysis of the binding mode of Ac-CoA to ckcACD1 provides insight into substrate specificity of the enzyme.     

ERCP对原发性肝外胆管癌的诊断价值

ＥＲＣＰ检查梗阻性黄疸２８７例中原发性肝外胆管癌４８例，其中胆囊癌４例（８％），肝总管癌１１例（２３％），胆总管癌１２例（２５％），壶腹癌１７例（３６％），胆管多部位癌４例（８％）。另外胰头癌浸润胆总管５例。本文探讨了原发性肝外胆管癌的Ｘ线特征、鉴别诊断；对比分析了ＥＲＣＰ与Ｂ超的诊断价值。     

鸟-胞内分枝杆菌复合群与龟-脓肿分枝杆菌肺病并发支气管扩张的CT征象比较

目的 探讨鸟-胞内分枝杆菌复合群(MAC)肺病与龟-脓肿分枝杆菌肺病并发支气管扩张患者CT征象的差异,提高对两种疾病并发支气管扩张的鉴别诊断水平。 方法 搜集2017年1—12月在广州市胸科医院门诊及住院治疗并经临床确诊的25例并发支气管扩张的鸟-胞内分枝杆菌复合群肺病患者(简称“A组”)和26例并发支气管扩张的龟-脓肿分枝杆菌肺病患者(简称“B组”),两组患者均为初诊或未经抗结核和抗非结核分枝杆菌(NTM)治疗。对两组患者的CT扫描资料进行回顾性分析,主要就两组患者支气管扩张(CT分型、分布)、肺内病灶的形态(微结节、树芽征、结节、实变等)、伴发空洞(类型、分布)的CT征象特点及并发症发生情况进行对比分析。 结果 B组左肺下叶支气管扩张、左肺下叶微结节、肺体积收缩的比率分别为57.69%(15/26)、84.62%(22/26)、61.54%(16/26),均明显高于A组[分别为28.00%(7/25)、56.00%(14/25)、32.00%(8/25)],差异均有统计学意义(χ ²值分别为4.58、5.03、4.46,P值分别为0.032、0.025、0.035)。A组柱状型支气管扩张占52.00%(13/25),高于B组(15.38%,4/26);B组囊状型支气管扩张占50.00%(13/26),高于A组(16.00%,4/25),差异均有统计学意义(χ ²值分别为7.69、6.63,P值分别为0.006、0.010)。结论 龟-脓肿分枝杆菌肺病患者的CT表现中,左肺下叶支气管扩张、左肺下叶微结节、肺体积收缩的发生率高于MAC肺病患者;龟-脓肿分枝杆菌肺病多并发囊状型支气管扩张,而MAC肺病多并发柱状型支气管扩张,以上特征性CT征象有助于两种疾病的鉴别。     

树芽征在CT影像诊断肺结核中的应用

目的　探讨肺结核“树芽征”的CT影像特点。方法 对216例肺结核行螺旋CT检查,对各种类型肺结核病“树芽征”的形态、部位进行统计分析。结果 涂阳肺结核和空洞性肺结核的树芽征出现率分别为84.5%和92.3%,结核球的树芽征出现率为18.2%。空洞性肺结核树芽征分布:跨叶分布的频率占66.7%,对侧累积率为52.6%。结论 树芽征是肺结核经气道播散的特征影像,在不同结核病理阶段可表现不同形态和分布。     

山东省克山病病情及发病相关因素5年动态观察

目的 观察克山病病情和发病相关因素动态变化，为科学的指导克山病防治研究提供依据。方法 在山东克山病重病区莒县安庄和邹城市张庄设立2个监测点，自2000年起对3～14岁的1049例多发人群和点区县克山病病情进行连续5年动态监测，观察人群全部进行临床检查、心电图检查，可疑病人行X线胸部摄片，并对监测居民内、外环境（发、小麦、玉米、地瓜干）硒水平、经济情况及人均占有粮食进行了调查。结果 5年间2县无急型、亚急型发病，原有慢型97例，死亡10例，新发病5例。多发人群克山病检出率2000、2002及2004年安庄点依次为3．31％、4．86％、4．45％，张庄点为3．69％、4．86％、4．45％。异常心电图检出率2000、2002及2004年安庄点依次为3．31％，7．16％，5．39％；张庄点为6．38％，4．55％，5．27％。发硒水平逐年升高，粮食硒含量基本恒定。经济收入和人均占有口粮逐年增加，达137．9％。260．0％。结论 5年间克山病多发人群和点区县病情无明显变化，发病相关因素不断改善。     

严重急性呼吸综合征康复患者出院后随访CT分析

目的研究严重急性呼吸综合征（SARS）康复患者肺部残留病灶的CT表现及其转归。方法83例临床治愈患者出院1个月后进行X线胸片和CT检查，对肺部有病灶的病例间隔2个月后再次复查X线胸片和CT．对两次随访检查结果进行对比并分析肺部残留病灶与SARS类型的关系。结果30．1％（25／83）病例肺部存在残留病灶．CT表现包括磨玻璃影6例，网状影5例，片状影3例，索条影2例．磨玻璃影和卜述其他病灶混合影9例，2个月后复查除两例外均有不同程度吸收；SARS重型病例肺部残留病灶比例（36．8％）高于普通型（15．4％），两者差异有统计学意义。结论部分临床治愈SARS患者肺部仔在残留病灶，CT表现以磨玻璃影、网状影为主．SARS重型病例肺部残留病灶比例高于普通型，这些病灶经治疗大部分有不同程度吸收。     

Observation of femtosecond X-ray interactions with matter using an X-ray–X-ray pump–probe scheme

Resolution in the X-ray structure determination of noncrystalline samples has been limited to several tens of nanometers, because deep X-ray irradiation required for enhanced resolution causes radiation damage to samples. However, theoretical studies predict that the femtosecond (fs) durations of X-ray free-electron laser (XFEL) pulses make it possible to record scattering signals before the initiation of X-ray damage processes; thus, an ultraintense X-ray beam can be used beyond the conventional limit of radiation dose. Here, we verify this scenario by directly observing femtosecond X-ray damage processes in diamond irradiated with extraordinarily intense (∼10¹⁹ W/cm²) XFEL pulses. An X-ray pump–probe diffraction scheme was developed in this study; tightly focused double–5-fs XFEL pulses with time separations ranging from sub-fs to 80 fs were used to excite (i.e., pump) the diamond and characterize (i.e., probe) the temporal changes of the crystalline structures through Bragg reflection. It was found that the pump and probe diffraction intensities remain almost constant for shorter time separations of the double pulse, whereas the probe diffraction intensities decreased after 20 fs following pump pulse irradiation due to the X-ray–induced atomic displacement. This result indicates that sub-10-fs XFEL pulses enable conductions of damageless structural determinations and supports the validity of the theoretical predictions of ultraintense X-ray–matter interactions. The X-ray pump–probe scheme demonstrated here would be effective for understanding ultraintense X-ray–matter interactions, which will greatly stimulate advanced XFEL applications, such as atomic structure determination of a single molecule and generation of exotic matters with high energy densities.Since W. C. Röntgen discovered X-rays emitted from vacuum tube equipment in 1895, scientists have continuously endeavored to develop brighter X-ray sources throughout the 20th century. One of the most remarkable breakthroughs was the emergence of synchrotron light sources, which were much more brilliant than the early lab-based X-ray sources. Such dramatic increase in X-ray brilliance provided a pathway to obtain high-quality X-ray scattering data. This, in turn, enabled one to solve the structures of complex systems such as proteins, functional units of living organisms, and viruses. However, the increase in the brilliance is also accompanied by a severe problem of X-ray radiation damage to the samples being examined (1). X-rays ionize atoms and generate highly activated radicals that break chemical bonds and cause changes in the structures of the samples. To achieve structure determination precisely, a sufficient scattering signal should be recorded before the samples are severely damaged. Radiation damage was considered to be an intrinsic problem associated with X-ray scattering experiments, which imposed a fundamental limit on the resolution in X-ray structure determination (2).The recent advent of X-ray free-electron lasers (XFELs) (3–5), which emit ultraintense X-ray pulses with durations of several femtoseconds, may totally avoid the problem of radiation damage. The irradiation of intense XFEL pulses generates highly ionized atoms, and the strong Coulomb repulsive force leads to evaporation of the samples. Meanwhile, it has been predicted theoretically (6) that atoms do not change their positions before the termination of the femtosecond X-ray pulse owing to inertia, thus enabling the use of X-ray radiations beyond the conventional X-ray dose limit. This innovative concept, called a “diffraction-before-destruction” scheme (6, 7), has paved a clear way to high-resolution structure determinations of weak scattering objects, including nanometer-sized protein crystals (8), noncrystalline biological particles (9), and damage-sensitive protein crystals (10).Despite the potential impact of XFELs, detailed understanding of the ultrafast XFEL damage processes has been missing. As a pioneering work, Barty et al. (11) measured the diffraction intensities of protein nanocrystals by changing the XFEL pulse durations from 70 to 300 fs at intensities of ∼10¹⁷ W/cm². They found that the diffraction intensities greatly decrease for longer durations, clearly indicating sign of structural damage, i.e., X-ray–induced atomic displacements within the XFEL pulse durations. For further understanding of ultraintense X-ray interactions with matter, we need to directly measure the temporal changes of the structural damage. In particular, measuring the ignition time of the atomic displacements is crucial for realizing advanced applications with greatly intense XFELs. Although improving our knowledge of the X-ray damage processes is essential for all aspects of XFEL science, the experimental verifications have been missing because of the extreme difficulty in observation with ultrahigh resolutions in space (ångstrom) and time (femtosecond).As a new approach to investigate the femtosecond X-ray damage processes, we here propose an X-ray–X-ray pump–probe experiment using double X-ray pulses; a pump X-ray pulse excites a sample and a probe X-ray pulse with a well-controlled time delay characterizes the change in the sample. In this approach, it is highly useful to exploit two-color double pulses with tunable temporal separations (12–15), which have been developed at SPring-8 Angstrom Compact free-electron LAser (SACLA) (4) and Linac Coherent Light Source (3). In this article, we measured the X-ray damage processes of diamond by using an X-ray–X-ray pump–probe diffraction experiment at SACLA. As the carbon–carbon bond is one of the most fundamental bonds in biomolecules, our results should provide a benchmark for XFEL-induced damage to practical samples.     

Structural basis for membrane binding and catalytic activation of the peripheral membrane enzyme pyruvate oxidase from Escherichia coli

The thiamin- and flavin-dependent peripheral membrane enzyme pyruvate oxidase from E. coli catalyzes the oxidative decarboxylation of the central metabolite pyruvate to CO₂ and acetate. Concomitant reduction of the enzyme-bound flavin triggers membrane binding of the C terminus and shuttling of 2 electrons to ubiquinone 8, a membrane-bound mobile carrier of the electron transport chain. Binding to the membrane in vivo or limited proteolysis in vitro stimulate the catalytic proficiency by 2 orders of magnitude. The molecular mechanisms by which membrane binding and activation are governed have remained enigmatic. Here, we present the X-ray crystal structures of the full-length enzyme and a proteolytically activated truncation variant lacking the last 23 C-terminal residues inferred as important in membrane binding. In conjunction with spectroscopic results, the structural data pinpoint a conformational rearrangement upon activation that exposes the autoinhibitory C terminus, thereby freeing the active site. In the activated enzyme, Phe-465 swings into the active site and wires both cofactors for efficient electron transfer. The isolated C terminus, which has no intrinsic helix propensity, folds into a helical structure in the presence of micelles.