Characterization of the amino acids of bovine fibrinogen involved in the fibrinogen-thrombin interaction of the blood clotting process. Comparison with the milk clotting process

Summary Bovine fibrinogen and the A and B chains of bovine fibrinogen have been subjected to chemical modification by a number of reagents and the effects of these procedures on the susceptibility of the proteins to thrombin hydrolysis is described. The reagents used were rose bengal (for photo-oxidation), 2-hydroxy-5-nitrobenzyl bromide, N-acetylimidazole, iodoacetic acid and diethyl pyrocarbonate. Evidence is presented which indicates that the tryptophan and tyrosine residues of fibrinogen are not involved to any great extent in the interaction of this protein with thrombin. Modification with iodoacetic acid suggests that methionine residues play a major role in such interactions, but the fibrinogen chains on which the important residues reside remain uncertain. The use of diethyl pyrocarbonate indicates the participation also of histidine in fibrinogen-thrombin interactions and that, whereas the histidine residues of the B chain are involved to a great extent, it appears that those of the Aa chain are not. The similarities which exist between the fibrinogen-thrombin and the -casein-chymosin systems are discussed.Abbreviations used DEP diethyl pyrocarbonate (ethoxyformic anhydride) - HNBB 2-hydroxy-5-nitrobenzyl bromide - N-Acl N-acetylimidazole - PTC phenylthiocarbamyl - PTH 3-phenyl-2-thiohydantoin.     

Time resolved spectroscopy of the tryptophyl fluorescence of the E. coli LAC repressor.

A new crystal form of a mitogenic lectin from pea seeds ($\text{Pisum sativum}$) has been obtained which is suitable for high resolution structural work. The crystals are orthorhombic, space group P2₁2₁2₁, with unit cell dimensions: $\text{a}$ = 64.2Å, $\text{b}$ = 72. 7Å, $\text{c}$ = 108. 3Å. The asymmetric unit contains one protein molecule.     

Trophoblastin, an antiluteolytic protein present in early pregnancy in sheep.

Trophoblastin, an antiluteolytic component from the embryo, was identified in the ewe by the means of intrauterine injections of homogenates from trophoblasts at 14--16 days pregnancy. Homogenates from embryos and their membranes at 21--23 days pregnancy did not extend the life of the corpus luteum, suggesting that trophoblastin synthesis occurs for only a short period. The trophoblastin was thermolabile (80 degrees C for 30 min) and inactivated by pronase. Treatment of ewes with oCS, hCG, and extracts of 120-day placentae did not affect the time of luteolysis. The protein appears to be insoluble at pH 7 or 8, but to dissolve readily at pH 9.6. After injection of homogenates or extracts from 15--16-day-old trophoblasts, the initial CL were maintained for more than 1 month in most cyclic recipient ewes. Surgical removal of embryos at 21--23 days resulted in luteal maintenace for more than 1 month in over 50% of the operated animals. All the maintained CL were secretory although their average weight was about one-half of that CL of normal pregnancy, suggesting the existence of complementary luteotrophic placental factors. The uteri of most of these pseudopregnant ewes were distended with a clear, sterile fluid.     

On the infrastructural localization of basic proteins in the nucleus and nucleolus of cells in pea axillary meristems submitted to or released from apical dominance

Summary In pea axillary meristems submitted to or released from apical dominance, basic nuclear proteins and their fractions (lysine or arginine-rich) were localized at the infrastructural level using convergent methods. In the inhibited nuclei, the condensed chromatin and the nucleoli are the most reactive regions to alcoholic solution of phosphotungstic acid and to ammoniacal silver nitrate. It is the same in the reactivated nuclei after the release from dominance, but the increase in diameter of the nucleoli is accompanied by the creation of a granular component which is observed around the nucleoli during the G₁ S or G₂ phases. This structure is built up essentially by a lysin-rich ribonucleoprotein complex characteristic of active nuclei.     

Phenotypic exclusion in mouse melanoma-rat hepatoma hybrid cells: pigment and albumin production are not reexpressed simultaneously.

Hybridization of cells of defined and different histotypes has been carried out to investigate whether the expression (or reexpression) of parental functions is mutually exclusive, as is expected if the generally assumed rule of discreteness of differentiation applies to hybrid cells. A cross of pigmented mouse melanoma cells and albumin-producing rat hepatoma cells gave rise to hybrids containing essentially one set of chromosomes from each parent and producing neither melanin nor albumin. Cells of one hybrid clone are shown to retain the potential to reexpress both parental differentiations. Successive subclonings of this hybrid have shown that cells which reexpress one function may retain the potential to reexpress the other, and that freshly isolated, morphologically homogeneous subclones may produce pigment or albumin, but not both; there successive and exclusive shifts of phenotype are documented, and in these cases, chromosome loss is very slight. The use of immunoadsorbed antisera has revealed that most (if not all) of the albumin produced by the hybrid cells is of the mouse type. We conclude that both parental determinations are retained by the hybrid cells, and that the parental differentiations are reexpressed only in a mutually exclusive fashion.