Selective inhibition of thrombin by (2R,4R)-4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl++ +) sulfonyl]-l-arginyl)]-2-piperidinecarboxylic acid

The potency of thrombin inhibition by 4-methyl-1-[N2-[(3-methyl-1,2,3,4-tetrahydro-8-quinolinyl)-sulfony l]- L-arginyl]-2-piperidinecarboxylic acid (MQPA) depended on the stereoconformation of the 2-piperidinecarboxylic acid moiety. Ki values for bovine alpha-thrombin were 0.019 microM with (2R,4R)-MQPA, 0.24 microM with (2R,4S)-MQPA, 1.9 microM with (2S,4R)-MQPA, and 280 microM with (2S,4S)-MQPA. (2R,4R)-MQPA of the four stereoisomers of MQPA was also the most potent inhibitor for other trypsin-like serine proteases with Ki values of 5.0 microM for trypsin, 210 microM for factor Xa, 800 microM for plasmin, and 1500 microM for plasma kallikrein. Examination of the potency of thrombin inhibition by arginine derivatives related to MQPA in structure suggested the presence of a specific binding site for the carboxamide portion (C-terminal side). The relative inhibitory potency of the four stereoisomers of MQPA for trypsin was nearly identical with that for thrombin, suggesting that the specific binding site for the carboxamide portion is present in both enzymes. Modification of thrombin by phosphopyridoxylation or the presence of heparin did not significantly alter the binding of MQPA.     

Respiration and avoidance reaction of a cyprinid fishPseudogobio esocinus under hypoxia

A cyprinid fish,Pseudogobio esocinus showed gradual bradycardia at oxygen saturation (%) of less than 29.7±4.6 (1.89±0.29 ml/l of oxygen concentration), surfacing at 14.7±1.3 (0.94±0.09ml/l), drastic decrease of oxygen consumption at less than 14.2±0.8 (0.91 ±0.06ml/l) and asphyxia at 9.7±1.4 (0.62±0.09ml/l). The fish avoided water having low oxygen saturation of less than 54.0± 5.4 (3.38±0.30ml/l), and markedly at less than 26.2±3.4 (1.62±0.16 ml/l).     

Similarities between rat liver mitochondrial and cytosolic glutathione reductases and their apoenzyme accumulation in riboflavin deficiency

Glutathione reductase has been purified 5,500-fold from rat liver mitochondrial matrix in a yield of 30%. The mitochondrial enzyme was immunochemically indistinguishable from that of the cytosol and the subunit molecular weight was apparently similar to that of the cytosolic enzyme, that is, 50,000 daltons. The optimum pH and kinetic properties investigated were not significantly different from those of the cytosolic enzyme. When rats were fed a riboflavin-deficient diet, the enzyme activity in the mitochondria decreased to a greater extent than that in the cytosol, and greater accumulation of apo-enzyme in the former than that in the latter was confirmed by the amount of immunoprecipitable protein, activation by FAD addition in vitro, and the enzyme activity recovery after injection of riboflavin, into riboflavin-deficient rats.     

Complement-dependent cytotoxic factor to megakaryocyte progenitors in sera from patients with idiopathic thrombocytopenic purpura

The influence of sera from patients with idiopathic thrombocytopenic purpura (ITP) was examined on colony formation from megakaryocyte (M) progenitors. Though incubation of marrow cells in Iscove's modified Dulbecco's medium (IMDM) containing 50% sera from several ITP patients stimulated M-colony formation in 8 of 13 cases, incubation in the sera from the patients and in baby rabbit serum as a source of complement significantly suppressed the colony formation. Experiments showed that sera of immunoglobulin G from ITP patients had significant complement-dependent cytotoxicity to M-progenitors in normal marrow cells or in the marrow cells from corresponding patients, but not to CFU-e, BFU-e or CFU-gm. Cytospin preparations of individually collected M-colonies from marrow cells treated with ITP patients' sera and complement revealed a reduction of megakaryocyte colonies containing cells of multilineages. These results indicate that autoantibodies detected in ITP patients can bind not only to platelets and megakaryocytes, but may also bind to M-progenitors.     

Amino acid sequences of two trypsin inhibitors from winged bean seeds (Psophocarpus tetragonolobus (L)DC.)

The trypsin inhibitor (WTI-1) purified from winged bean seeds is a Kunitz type protease inhibitor having a molecular weight of 19,200. WTI-1 inhibits bovine trypsin stoichiometrically, but not bovine alpha-chymotrypsin. The approximate Ki value for the trypsin-inhibitor complex is 2.5 X 10(-9) M. The complete amino acid sequence of WTI-1 was determined by conventional methods. Comparison of the sequence with that of soybean trypsin inhibitor (STI) indicated that the sequence of WTI-1 had 50% homology with that of STI. WTI-1 was separated into 2 homologous inhibitors, WTI-1A and WTI-1B, by isoelectric focusing. The isoelectric points of WTI-1A and WTI-1B were 8.5 and 9.4, respectively, and their sequences were presumed from their amino acid compositions.     

High pressure NMR studies of hemoproteins. The effect of pressure on the tertiary and quaternary structures of human adult ferrous hemoglobin

The effect of pressure on the tertiary and quaternary structures of human oxy, carbonmonoxy, and deoxyhemoglobin was examined by high pressure NMR spectroscopy at 300 MHz. The increased pressure displaced the ring current-shifted gamma 1-methyl resonance of beta E11 valine for oxy- and carbonmonoxyhemoglobin to the upfield side, whereas that of the alpha subunit was insensitive to pressure. Such a preferential pressure-induced upfield shift for the beta E11 valine gamma 1-methyl signal was also encountered for the isolated carbonmonoxy beta chain. For deoxyhemoglobin, hyperfine shifted resonances of the heme peripheral proton groups and the proximal histidyl NH proton for the beta subunit were pressure-dependent, in contrast to the pressure-insensitive responses for these resonances of the alpha subunit. These results indicate the structural nonequivalence of the pressure-induced structural changes in the alpha and beta subunits of hemoglobin. The exchangeable proton resonances due to the intra- and intersubunit hydrogen bonds which have been used as the oxy and deoxy quaternary structural probes were not changed upon pressurization. From all of above results, it was concluded that pressure induces the tertiary structural change preferentially at the beta heme pocket of the ferrous hemoglobin derivatives with the quaternary structure retained.     

Squid retinochrome. Configurational changes of the retinal chromophore.

The configurations of the retinal chromophore in light and dark reactions of squid retinochrome were investigated by means of high-performance liquid chromatography. Orange light isomerized the chromophore of retinochrome, all-trans-retinal, mainly to the 11-cis configuration in metaretinochrome. Irradiation with shorter-wavelength lights not only accelerates the photoreversal of metaretinochrome to retinochrome but also leads to a slight production of isoretinochrome (13-cis-retinochrome), yielding a photoequilibrium mixture of three kinds of retinochrome. 13-cis- and 9-cis-retinochromes are photosensitive, and are converted into metaretinochrome upon irradiation with orange light. When steadily exposed to orange light in the presence of a trace of retinochrome-protein, all of the all-trans-, 13-cis-, and 9-cis-retinals are catalytically isomerized only to the 11-cis form, although the reaction rate is reduced in the order of the retinals listed above. In the dark, 9-cis-retinochrome, like retinochrome, remains unchanged, but both meta- and 13-cis-retinochromes slowly change to retinochrome. The chromophore of 13-cis-retinochrome changes directly to the all-trans form, whereas the 11-cis chromophore of metaretinochrome goes to all-trans mainly through the 13-cis form. The direct isomerization from 11-cis to all-trans hardly occurs at temperatures as low as 20 degrees C, and shows high values of the activation enthalpy and entropy changes. Based upon these findings, the role of retinochrome in the photoreception of the visual cells is discussed.     

Guanosine 5'-triphosphate, 3'-diphosphate 5'-phosphohydrolase. Purification and substrate specificity

The regulatory nucleotide guanosine 5'-diphosphate, 3'-diphosphate (ppGpp) and its precursor guanosine 5'-triphosphate, 3'-diphosphate (pppGpp) are accumulated during stringent response in bacterial cells. The enzyme pppGpp-5'-phosphohydrolase, which catalyzes the conversion of pppGpp to ppGpp, was partially purified from Escherichia coli. It has Mr = 140,000 and an apparent Km of 0.11 mM for pppGpp. It requires Mg2+ and a monovalent cation. NH4+ is preferred over K+, while Na+ is inactive. The enzyme does not hydrolyze GTP, ATP, pppApp, or ppGpp. It is also not effectively inhibited by these nucleotides. pppGpp-5'-phosphohydrolase hydrolyzes the 3'-monophosphate analog pppGp equally well (apparent Km of 0.13 mM), yielding the recently identified MS III nucleotide (ppGp). pppGpp-5'-phosphohydrolase does not have RNA 5'-terminal gamma-phosphatase activity; however, 5'-terminal phosphates are released by pppGpp-5'-phosphohydrolase when the GTP-terminated RNA chains are first converted into oligonucleotides by RNase A treatment. pppGpp-5'-phosphohydrolase was found to actively hydrolyze the dinucleotide fragment pppGpNp but exhibited very low activity toward longer chain fragments. The 3'-unphosphorylated dinucleotide pppGpN was, however, not hydrolyzed. The ability of pppGpp-5'-phosphohydrolase to hydrolyze pppGpp, pppGp, and pppGpNp, but not pppG and pppGpN, indicates that pppGpp-5'-phosphohydrolase is rather nonspecific toward the 3'-OH substitutions of the substrates although a free, unsubstituted phosphate group at the 3'-OH position is essential.     

Improvement of first-service pregnancy rate in cows with gonadotropin-releasing hormone analog

The effect of an intramuscular injection of a new analog of gonadotropin-releasing hormone (GnRH), fertirelin, on the first-service pregnancy rate in cows was investigated by a double blind experiment. A total of 1,194 cows was injected intramuscularly either with 100 mug of GnRH or placebo (physiological saline solution) at the time of first insemination postpartum. Pregnancy rate (number of cows calved/ number of cows serviced) was 57.2 % in 605 cows treated with GnRH, while the performance was 49.7 % in 589 cows of the placebo group. The difference of pregnancy rates in both groups was significant (P<0.05). GnRH injected at insemination was effective, especially in cows at the first and third lactations, cows at 101 days postpartum or later, cows with daily milk yield of 26-30 kg, and also in cows from the area where a regional average fertility was relatively low.