The effect of nitrate and nitrite on fluorescence spectra of whole cells of the filamentous blue-green alga Anabaena sp. strain 7119 was investigated under different conditions. Emission spectra of cells excited with ...
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The effect of nitrate and nitrite on fluorescence spectra of whole cells of the filamentous blue-green alga Anabaena sp. strain 7119 was investigated under different conditions. Emission spectra of cells excited with light of 590 nm under argon atmosphere exhibit high levels of PS [photosystem] II Chl [chlorophyll] a and phycobilin fluorescence. Switching to aerobic conditions or addition, under anaerobic conditions, of either nitrate or nitrite to nitrate-grown cells induces a strong quenching of PS II Chl a fluorescence (685 nm) and a weak one of PS I Chl a (740 nm), without significantly affecting phycobilin fluorescence (66770 nm). Ammonia-grown cells, which lack the nitrate-reducing enzyme system, exhibit likewise Chl a fluorescence quenching by oxygen but are not responsive to either nitrate or nitrite. The addition of DCMU [3-(3,4-dichlorophenyl)-1,1-dimethylurea] increses Chl a fluorescence. In the presence of this inhibitor, however, neither nitrate or nitrite is able to promote its typical quenching effect. Upon excitation at different wavelengths, both nitrogenous compounds also bring about quenching of Chl a fluorescence, the excitation spectra being analogous to the absorption spectrum of phycobilins. These facts correlate Chl a fluorescence with the photochemical reactions involved in the ferredoxin-dependent enzymatic reduction of nitrate and nitrite in blue-green algae.
The effects of extracellular Ca2+ concentration and the putative antagonist of intracellular Ca2+ movement 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) on platelet phospholipase activity and thromboxane ...
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The effects of extracellular Ca2+ concentration and the putative antagonist of intracellular Ca2+ movement 8-(N,N-diethylamino)octyl-3,4,5-trimethoxybenzoate (TMB-8) on platelet phospholipase activity and thromboxane B2 synthesis were examined in rabbit platelets stimulated by platelet activating factor, thrombin and ionophore A23187. TMB-8 markedly inhibited the platelet activating factor-induced decrease in [14C]arachidonate content in platelet phosphatidylcholine and phosphatidylinositol, while showing minimal effects on thrombin-induced phospholipase activation. A23187 stimulation of these processes was inhibited to an intermediate all 3 stimuli. The threshold concentration of extracellular Ca2+ for phospholipase activation as measured by thromboxane B2 synthesis, was similar for platelet activating factor- and thrombin-stimulated platelets. While platelet activating factor and thrombin may have similar requirements for extracellular Ca2+, they utilize a TMB-8 sensitive step to different degrees during activating of platelet phospholipase.
Dicyclohexylcarbodiimide (DCCD), a potent inhibitor of the f0f1[complex consisting of a section intrinsic to the membrane (f0) that functions as an H+ channel and a multi-subunit complex extrinsic to the membrane (f1)...
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Dicyclohexylcarbodiimide (DCCD), a potent inhibitor of the f0f1[complex consisting of a section intrinsic to the membrane (f0) that functions as an H+ channel and a multi-subunit complex extrinsic to the membrane (f1) that is the catalytic (ATP hydrolase) component]-type H+-translocating ATPase, was employed to determine the possible involvement of such an ATPase in urinary acidification. Two methods were used in this approach: the reaction of [14C]DCCD with tissues involved in urinary acidification and the inhibition of ATPase activity by DCCD. Membrane components from epithelial cells of toad and turtle urinary bladder and brush borders of rabbit kidney were reacted with [14C]DCCD and analyzed by polyacrylamide gel electrophoresis both before and after extraction with organic solvents. Although a DCCD-binding component was extracted from toad and turtle bladder membranes by chloroform/methanol (2:1, vol/vol), the binding was not saturable. Analysis of this DCCD-binding component by TLC indicated that there was no ninhydrin reactivity associated with the [14C]DCCD binding. All attempts to precipitate a DCCD-binding protein were unsuccessful. Apparently, the observed DCCD binding was to phospholipid. In the 2nd type of experiment, the ATPase activity present in brush borders from rabbit kidney was partially inhibited by DCCD, but at a concentration that is over 2 orders of magnitude greater than that required for typical DCCD-sensitive ATPase. Because of the failure in finding positive evidence of a DCCD-reactive protein and from the relative insensitivity of the ATPase to DCCD, either urinary acidification may not be accomplished by a typical f0f1-type translocating ATPase, or the f0 maybe modified so that the sensitivity to DCCD was altered or lost.
作者：
LIBER, HLTHILLY, WGMIT
DEPT NUTR & FOOD SCI GENET TOXICOL GRP CAMBRIDGE MA 02139 USA
A thymidine kinase heterozygote was isolated from a diploid human lymphoblast line which forms colonies with high efficiency in microtiter dishes. This cell line, called TK6, can be mutated from a TK+/- to TK-/- state...
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A thymidine kinase heterozygote was isolated from a diploid human lymphoblast line which forms colonies with high efficiency in microtiter dishes. This cell line, called TK6, can be mutated from a TK+/- to TK-/- state by diverse mutagens, including ethyl methanesulfonate, butyl methanesulfonate, nitrosomethylurea, UV light, ICR-191, 4-nitroquinoline oxide, fluorodeoxyuridine, benzo[a]pyrene and aflatoxin B1. The experiments required to demonstrate the applicability of this new line in quantitative assays of mutation in human cells are reported. Mitotic recombination between the centromere and the tk locus could not be induced by either dimethylsulfoxide or phorbol-12-myristate-13-acetate.
Eggs laid by 153 Gd-labeled Japanese quail were collected each day for 24 days. Maximum transference of the lanthanide to an oocyte approximated 27% of the dose given the quail and usually occurred for the egg collect...
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Eggs laid by 153 Gd-labeled Japanese quail were collected each day for 24 days. Maximum transference of the lanthanide to an oocyte approximated 27% of the dose given the quail and usually occurred for the egg collected on the 3rd day. The 24 largest oocytes from 2 quails were removed 18 h after labeling. The curve for a plot of percent 153Gd vs. oocyte for these 24 oocytes approximated a log-log function. Eggs doubly-labeled with 153Gd and Sudan black B showed no label in the latebra. Quail hatched from labeled eggs were dissected at various times up to 67 days of age. The percent of egg 153Gd that was found in the f1 quail decreased from 100% to approximately 55% during the 1st 14 days. Recovery for mature quail was 55.8%. The major portion of 153Gd present in each f1 quail was found in the yolk sac and ranged from 96.0% for hatchlings a few hours old to 73.3% for mature quail. The weight of the yolk sac decreased from 0.7 g for hatchilings to 0.04 g for mature quail. The 1st 5 eggs laid by producing f1 quail contained a total of 0.643% of 153Gd in these quail. The graph curve for these eggs for percent 153Gd vs. day of collection approximated an exponential function, in contrast to the marked maximum seen for 153Gd levels in eggs laid by the parent quail.
In common with the f1-ATPase from other sources, yeast mitochondrial f1-ATPase was inhibited by 4-chloro-7-nitrobenzofurazan. Total inhibition of the f1-ATPase activity was compatible with the modification of a single...
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In common with the f1-ATPase from other sources, yeast mitochondrial f1-ATPase was inhibited by 4-chloro-7-nitrobenzofurazan. Total inhibition of the f1-ATPase activity was compatible with the modification of a single tyrosine residue per f1-ATPase molecule. Radioactive labeling experiments localized this modification on a .beta.-subunit. The inactive modified enzyme retained the capacity to bind the photoaffinity label 8-azido-1,N6-etheno-ATP, which was previously shown to bind nucleotide sites of low affinity. The inactive modified enzyme bound Mg-ATP with high affinity, yielding a Kd of 14 .mu.M. The hypothesis of alternating, or cooperative, site catalysis by f1-ATPase was confirmed.
Previous work has shown that mild trypsin treatment eliminates energy-transduction capability and tight (non-exchangeable) nucleotide binding in beef heart mitochondrial f1-ATPase. The structural change brought about ...
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Previous work has shown that mild trypsin treatment eliminates energy-transduction capability and tight (non-exchangeable) nucleotide binding in beef heart mitochondrial f1-ATPase. The structural change brought about by trypsin was, however, too subtle to be identified by 1-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis [SDS-PAGE] and was not defined. In this work 2-dimensional electrophoresis (isoelectric focusing then SDS-PAGE) was applied to the problem, and it was determined that the .alpha.-subunit off1 is altered by the mild trypsin treatment, whereas no change was detected in .beta.-, .gamma.-, .delta.- or .epsilon.-subunits. Binding of ADP to the trypsin-treated f1 was compared to binding to control enzyme over a range of 0-40 .mu.M ADP in a 30 min incubation period. There was no difference between the 2 enzymes, KdADP in Mg2+-containing buffer was about 2 .mu.M in each. Since the tight (nonexchangeable) sites are abolished in trypsin-treated f1, this shows that tight exchangeable ADP-binding sites are different from the tight nonexchangeable ADP-binding sites. There was no effect of trypsin cleavage of the .alpha.-subunit on .beta.-subunit conformation as judged by aurovertin fluoresence studies. The cleavage of the .alpha.-subunit which occurred as judged to occur very close to the C- or N-terminus of the subunit and constitutes therefore a small and specific chemical modification which abolishes overall function in f1 but leaves partial functions intact.
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