Synthesis of 7-mercaptoheptanoylthreonine phosphate and its activity in the methylcoenzyme M methylreductase system

The structure of component B of the methylcoenzyme M methylreductase of Methanobacterium thermoautotrophicum was recently assigned as 7-mercaptoheptanoylthreonine phosphate (HS-HTP) (Noll, K. M., Rinehart, K. L., Jr., Tanner, R.S., and Wolfe, R.S. (1986) (Proc. Natl. Acad. Sci. U.S.A. 83, 4238-4242). We report here the chemical synthesis and biochemical activity of this compound. Thiourea and 7-bromoheptanoic acid were used to to synthesize 7,7'-dithiodiheptanoic acid. This disulfide was then condensed with DL-threonine phosphate using N-hydroxysuccinimide and dicyclohexylcarbodiimide. The product was reduced with dithiothreitol to give HS-HTP. It could be oxidized in air in the presence of 2-mercaptoethanol to give the compound as it was isolated from cell extracts. The resulting product was identical to the authentic compound by 1H NMR spectroscopy, mass spectrometry, and coelution using high performance liquid chromatography. The synthetic compound is active in the in vitro methanogenic assay at concentrations comparable to the authentic compound. This confirms the structure of component B as HS-HTP and provides a means to synthesize quantities sufficient for studies of the methylreductase system.     

Environment-specific amino acid substitution tables: tertiary templates and prediction of protein folds.

The local environment of an amino acid in a folded protein determines the acceptability of mutations at that position. In order to characterize and quantify these structural constraints, we have made a comparative analysis of families of homologous proteins. Residues in each structure are classified according to amino acid type, secondary structure, accessibility of the side chain, and existence of hydrogen bonds from the side chains. Analysis of the pattern of observed substitutions as a function of local environment shows that there are distinct patterns, especially for buried polar residues. The substitution data tables are available on diskette with Protein Science. Given the fold of a protein, one is able to predict sequences compatible with the fold (profiles or templates) and potentially to discriminate between a correctly folded and misfolded protein. Conversely, analysis of residue variation across a family of aligned sequences in terms of substitution profiles can allow prediction of secondary structure or tertiary environment.     

田螺科五种螺的核型研究

以早期胚胎细胞为材料,用火焰干燥法制片,对分布于我国湖北省武汉市近郊的常见田螺科(Viviparidae)五种螺的核型进行了分析。结果:两种圆田螺的染色体数和国外报道的同一属的种类的一致。而三种环棱螺的染色体数,则较国外报道的另两种的少得多。在铜锈环棱螺的核型中,其m组的第一对和sm组的第四对染色体上,具有明显的随体,出现频率甚高。     

Cellularity of organs in mature rams of different breeds

The relative importance of cell number and cell size in determining the mass of 16 organs and tissues in mature rams of six different breeds was studied through estimation of organ deoxyribonucleic acid (DNA) content. The mean fleece-free empty body weight (FFEBW) ranged from 54.6 +/- 0.3 kg for Camden Park Merinos to 76.7 +/- 1.6 kg for Strong Wool Merinos. For all organs, mass increased with FFEBW, but the relationship was significant across all sheep for only eight organs (blood, kidney, liver, abomasum, vastus lateralis muscle, skin, perirenal fat and triceps muscle). There were significant differences between breeds in the mass of 11 organs. With four (heart, rumen reticulum, small intestine and testicular fat) this difference was independent of breed differences in FFEBW, whereas with another four (kidney, abomasum, vastus lateralis muscle and skin), it was closely related to FFEBW. Breed differences in the mass of the remaining three organs (blood, liver and perirenal fat) were partly related to FFEBW and partly breed specific. Blood mass increased with FFEBW across all animals, but, within a breed, it declined as FFEBW increased. The increase in the mass of perirenal fat with FFEBW was significantly greater within a breed than between breeds. Cell number increased significantly with the mass of all organs except blood and brain. There were between-breed differences in the number of cells in seven organs (liver, heart, rumen reticulum, abomasum, small intestine, vastus lateralis muscle and skin), which, except for heart, were attributable to between-breed differences in organ mass. With heart, the increase in cell number with organ mass within a breed was greater than across all breeds. Cell size was significantly related to organ mass only with vastus lateralis muscle, spleen, perirenal fat and liver. The relationship for vastus lateralis muscle and spleen was negative, indicating that cells were smaller in larger organs. There were differences between breeds in cell size for heart, vastus lateralis and triceps muscles. These differences for heart and triceps muscle were breed specific, whereas for vastus lateralis muscle it was attributed to breed differences in organ weight. There was a 30-fold range in mean cell size across organs, with adipose tissue having the largest cells, muscle tissue intermediate and visceral tissues the smallest. In general, organ mass is positively related to FFEBW. Cell number, not cell size, is largely responsible for differences in organ mass between mature sheep of different breeds.     

Inhibition of cathepsin B by peptidyl aldehydes and ketones: slow-binding behavior of a trifluoromethyl ketone

Inhibition of the cysteine proteinase cathepsin B by a series of N-benzyloxycarbonyl-L-phenylalanyl-L-alanine ketones and the analogous aldehyde has been investigated. Surprisingly, whereas the aldehyde was found to be almost as potent a competitive reversible inhibitor as the natural peptidyl aldehyde, leupeptin, the corresponding trifluoromethyl ketone showed comparatively weak (and slow-binding) reversible inhibition. Evaluation of competitive hydration and hemithioketal formation in a model system led to a structure-activity correlation spanning several orders of magnitude in both cathepsin B inhibition constants (Ki) and model system equilibrium data (KRSH,apparent).     

Coenzyme F420 dependence of the methylenetetrahydromethanopterin dehydrogenase of Methanobacterium thermoautotrophicum

To identify the electron acceptor of the methylenetetrahydromethanopterin dehydrogenase of Methanobacterium thermoautotrophicum, we have purified the enzyme to homogeneity. The purified enzyme is absolutely dependent on coenzyme F420 (a 7,8-didemethyl-8-hydroxy-5-deazariboflavin derivative) for activity. Several alternative electron acceptors are ineffectual in the reaction. Changes in the absorption spectra of reaction mixtures indicate that 1.1 mol of coenzyme F420 is reduced per mol of substrate oxidized. The reaction is reversible and the equilibrium favors oxidation of methylenetetrahydromethanopterin.     

The anatomy of tissue cultured red raspberry prior to and after transfer to soil

The leaf, petiole, stem and root anatomy of an aseptically cultured red raspberry clone (Rubus idaeus L.) was studied before and 5 weeks after transfer to soil under controlled environmental conditions. Tissues persistent from culture showed little or no change with time in soil; they grew minimally and slight secondary wall deposition occurred. New organs formed in successive weeks after transplantation showed a graded increase in potential size and development. Some features, such as collenchyma formation, rapidly returned to control levels; this was seen in new leaves expanding in the first week after transplantation. Other features, such as sclerenchyma formation, did not occur in leaves expanding during the first 2 weeks after transplantation, even when these were a month or more in age. Some sclerenchyma was seen in leaves expanding in the third week after transplantation, increasing in later-formed leaves. Increasing the light intensity of transplant accelerated the return to control-type organ size and appearance. During acclimatization transitional forms of leaves, petioles, stems and roots develop that ranged anatomically from culture-to control-type. This trend is analagous to the normal developmental sequence of organ formation as it affects the potential for development of successily formed organs.     

中国鲤科鱼类染色体组型的研究 Ⅱ.鲴亚科四种鱼的染色体组型

鲴亚科(Xenocyprininae)鱼类多为中小型鱼类,常见于江河湖泊等较宽阔的水域中,我国长江、黑龙江、黄河及珠江诸流域皆有分布,共有10种,隶属4个属(伍献文等,1964)。迄今尚未见有该亚科鱼类染色体组型的研究报道。本文是对其中三属四种鱼的染色体组型的观察结果。这四种鱼是银鲴(Xenocypris argentea)、黄尾鲴(Xenocypris davidi)、细鳞斜颌鲴(Plagiognathops microlepis)和逆鱼(Acanthobrama simoni)。其中黄尾鲴和细鳞斜颌鲴均为新的淡水养殖鱼(沈德长等,1981;陈楚星,1979)。