Rapid determination of substrate specificity of Clostridium histolyticum beta-collagenase using an immobilized peptide library.

The molecular basis of the substrate specificity of Clostridium histolyticum beta-collagenase was investigated using a combinatorial method. An immobilized positional peptide library, which contains 24,000 sequences, was constructed with a 7-hydroxycoumarin-4-propanoyl (Cop) fluorescent group attached at the N terminus of each sequence. This immobilized peptide library was incubated with C. histolyticum beta-collagenase, releasing fluorogenic fragments in the solution phase. The relative substrate specificity (k(cat)/K(m)) for each member of the library was determined by measuring fluorescence intensity in the solution phase. Edman sequencing was used to assign structure to subsites of active substrate mixtures. Collectively, the substrate preference for subsites (P(3)-P(4)') of C. histolyticum beta-collagenase was determined. The last position on the C-terminal side in which the identity of the amino acids affects the activity of the enzyme is P(4)', and an aromatic side chain is preferred in this position. The optimal P(1)'-P(3)' extended substrate sequence is P(1)'-Gly/Ala, P(2)'-Pro/Xaa, and P(3)'-Lys/Arg/Pro/Thr/Ser. The Cop group in either the P(2) or P(3) position is required for a high substrate activity with C. histolyticum beta-collagenase. S(2) and S(3) sites of the protease play a dominant role in fixing the substrate specificity. The immobilized peptide library proved to be a powerful approach for assessing the substrate specificity of C. histolyticum beta-collagenase, so it may be applied to the study of other proteases of interest.     

Protistan microbial observatory in the Cariaco Basin,Caribbean. I. Pyrosequencing vs Sanger insights into species richness

Microbial diversity and distribution are topics of intensive research. In two companion papers in this issue, we describe the results of the Cariaco Microbial Observatory (Caribbean Sea, Venezuela). The Basin contains the largest body of marine anoxic water, and presents an opportunity to study protistan communities across biogeochemical gradients. In the first paper, we survey 18S ribosomal RNA (rRNA) gene sequence diversity using both Sanger- and pyrosequencing-based approaches, employing multiple PCR primers, and state-of-the-art statistical analyses to estimate microbial richness missed by the survey. Sampling the Basin at three stations, in two seasons, and at four depths with distinct biogeochemical regimes, we obtained the largest, and arguably the least biased collection of over 6000 nearly full-length protistan rRNA gene sequences from a given oceanographic regime to date, and over 80 000 pyrosequencing tags. These represent all major and many minor protistan taxa, at frequencies globally similar between the two sequence collections. This large data set provided, via the recently developed parametric modeling, the first statistically sound prediction of the total size of protistan richness in a large and varied environment, such as the Cariaco Basin: over 36 000 species, defined as almost full-length 18S rRNA gene sequence clusters sharing over 99% sequence homology. This richness is a small fraction of the grand total of known protists (over 100 000–500 000 species), suggesting a degree of protistan endemism.     

Quantitative assay of deoxyribonuclease activity after isoelectric focusing in polyacrylamide gels: pH control and effects of enzyme diffusion

A method for the quantitative assay of nuclease activity in crude cell lysates after isoelectric focusing (IEF) in polyacrylamide slab gels is described. After IEF, an agarose overlay gel containing DNA is placed on the IEF gel and the nuclease activity quantified by the loss of ethidium bromide fluorescence of the DNA. With this method a linear response was obtained for 1 to 10 ng of DNase I. Various methods of pH equilibration after IEF were also evaluated. The use of a high buffer concentration in the overlay gel is recommended to control the pH during the enzyme reaction. An analytical solution for the diffusion of enzymes from the IEF gel to the overlay gel is also presented and an equation that may be used to choose optimum times for transfer of the enzyme from the IEF gel to the overlay gel is given.     

Thrombin receptor occupancy initiates cell proliferation in the presence of phorbol myristic acetate

A combination of DIP-thrombin and either PMA (50 ng/ml) or dioctanoyl glycerol stimulates DNA synthesis in serum free cultures of NIL hamster cells similar to that previously reported for the combinatory effect of DIP-thrombin and gamma-thrombin. Thus, PMA or dioctanoyl glycerol appears to generate signals normally stimulated by gamma-thrombin interaction with cells. This stimulation was not observed when cells were treated with DIP-thrombin and 4-beta-phorbol or 4-alpha-phorbol 12,13-didecanoate. Therefore, it appears that this effect is mediated through activation of protein kinase C and that this activation plays an important role in thrombin mitogenesis.     

格网尺度下典型旅游城市生态服务价值估算和时空分异特征——以三亚为例

以典型旅游城市三亚市为案例地，利用2006-2018年4期Landsat遥感影像数据，借助ENVI、ArcGIS平台定量识别土地利用演变特征，在1km×1km格网尺度下估算旅游地生态系统服务价值，并结合空间探索性数据分析揭示生态系统服务价值时空分异特征及其与旅游地发展的时空耦合关系。结果表明：（1）2006-2018年间，三亚市生态系统服务价值总量呈逐年下降趋势，由6.73×10⁹元降至5.76×10⁹元，累计减少9.78×10⁸元；（2）空间格局上，三亚市呈"南低北高"空间分异格局，2006-2018年增值区域连片分布于崖州区、天涯区、吉阳区南部区域，且呈逐年减少趋势，减值区域集聚于天涯区东北部、海棠区；（3）空间集聚上，生态系统服务价值截面各年份均呈显著空间正相关且相关性先降后增。高高集聚区位于天涯区北部区域，低低集聚区分布于沿海、海湾地区；（4）旅游发展与生态系统服务价值时空演化特征关联性较强。三亚市天涯区北部林地生态环境良好，生态系统服务价值略有下降但绝对数值稳定，是生态系统服务价值主要来源；旅游发展较为迅速的三亚湾、崖州湾以及海棠湾，相对增值区域较多，但绝对生态系统服务价值损失显著，严重滞后于其他区域。     

The enzyme that cleaves apolipoprotein A-II upon in vitro incubation of human plasma high-density lipoprotein-3 with blood polymorphonuclear cells is an elastase

The proteolytic activity directed against apolipoprotein A-II (apo-A-II) which is released from human blood polymorphonuclear cells (PMN) when they are incubated with human plasma high-density lipoprotein-3 (HDL3) was studied to assess the properties and site specificity of the enzyme. When 125I-apo-A-II-labeled HDL3 was incubated with the PMN protease at 37 degrees C, a complete cleavage of apo-A-II was observed which paralleled the formation of bands of approximately 11,000 and 7,000 daltons by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The 7,000-dalton component had the following N-terminal sequence: NH2-Thr-Asp-Tyr-Gly-Lys-Asp-Leu-Met-Glu-Lys. This corresponds to residues 19 through 28 of the intact apo-A-II monomer. Methoxysuccinyl (MeO-Suc)-Ala-Ala-Pro-Val-chloromethylketone-(CH2Cl) caused a 90% inhibition of apo-A-II hydrolysis at the highest concentration tested (6 X 10(-4)M). Besides apo-A-II, the PMN enzyme also hydrolyzed a synthetic substrate, MeO-Suc-Ala-Ala-Pro-Val-4-nitroanilide and its 4-methylcoumaryl-7-amide analogue. The protease appeared to have a mass of 28,000 daltons as assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the [3H]diisopropylfluorophosphate-labeled PMN enzyme. That the PMN enzyme which cleaves apo-A-II is an elastase was derived from the following criteria: 1) cleavage at the Val-X bond in apo-A-II and in the two synthetic substrates studied; 2) prevention of the cleavage by MeO-Suc-Ala-Ala-Pro-Val-CH2Cl, a known specific elastase inhibitor; and 3) a mass comparable to that reported for a pure PMN elastase. These studies establish that apolipoproteins can be suitable substrates for enzymes of the elastase family.     

A preliminary investigation of prediction of mean arterial pressure after self-regulatory treatments.

This study investigated the ability of pretreatment variables from three different domains (social-demographic, psychological, and psychophysiological) to predict posttreatment mean arterial pressure (MAP) for 59 unmedicated males with mild hypertension who were participating in a cross-cultural (USA-USSR) comparison of autogenic training and thermal biofeedback to a self-relaxation control. The overall multiple regression equation consisted of two variables and indicated that higher diastolic blood pressures during a cold pressor task were predictive of greater MAP reductions while higher scores on the Irritability subscale of the Buss-Durkee Hostility Scale were predictive of less MAP reductions. Suggestions for future research in this area are provided.