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951.
952.
Two forms of a carbon monoxide-binding cytochrome were found to exist in CaCl2-precipitated microsomal subfractions of human placental homogenates at term. These exhibited absorption maxima at wavelengths of 450 nm and 421–432 nm. Conversion of P-450 to the degradation product could be prevented by resuspension of the microsomes in buffered solutions containing 20% glycerol and 10?4M dithiothreitol. Solubilization of such resuspended microsomes with sodium cholate could be effected with minimal degradation. The solubilized pigment then could be partially purified by differential fractionation with ammonium sulfate. The partially purified cytochromes did not appear to bind desmethylimpramine but did bind aniline and nicotinamide to yield atypical type II difference spectra with maxima at 435 nm and minima at 416 nm. A type I difference spectrum could be elicited with androstenedione and a spectral dissociation constant (KS) of 4.7×10?8M was obtained. Androstenedione also appeared to effectively prevent the binding of carbon monoxide to the cytochrome. 相似文献
953.
954.
955.
956.
957.
J Kirilovsky S Eimerl S Steiner-Mordoch M Schramm 《European journal of biochemistry》1987,166(1):221-228
Detergent-solubilized preparations of the beta-adrenergic receptor (R) and of the guanyl nucleotide binding proteins (Gs) were extensively treated to remove phospholipids and cholesterol. Reconstitution of an R-Gs system was subsequently performed in the presence of a mixture of natural phosphatidylethanolamine, phosphatidylcholine and phosphatidylserine or the synthetic dioleoyl derivatives of the same phospholipids. In both cases, an additional lipid was required for the agonist-dependent activation of Gs. The requirement could be fulfilled by alpha-tocopherol, or by unsaturated fatty acids such as oleic acid. Inclusion of this non-phosphorylated lipid in the reconstituted system enhanced the isoproterenol-dependent activation of Gs by guanosine 5'-O-[gamma-thio]triphosphate 16-33-fold. The rate of activation was largely dependent on the addition of the agonist. Efficient functional reconstitution of R-Gs was thus achieved in a totally defined lipid system. Additional studies of the reconstituted system and of the native membrane led to the notion that the non-phosphorylated lipid plays a role in the function of the hormone-R complex. 相似文献
958.
959.
VICTOR G. BRUCE 《The Journal of eukaryotic microbiology》1970,17(2):328-334
SYNOPSIS. Chlamydomonas reinhardi has a biological clock regulating phototaxis in dividing and non-dividing cultures; it also can exert some control on growth of continuous cultures. The period length is ∼ 24 hr; it is temperature-compensated and not dependent on the average growth rate. The rhythm can be entrained or phased by light-dark conditions. In dividing cultures a periodic fluctuation in cell number and total protein persists in continuous light. 相似文献
960.
Summary The iliofibularis muscle ofXenopus laevis is reported to contain five types of fibres which have different force—velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification.Maximum calcium-stimulated myofibrillar ATPase activity (V
max) and apparent Michaelis constant (K
m) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values forK
m andV
max.In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparentK
m for ATP. There was a tendency for high ATP concentrations in fibres with highK
m values.When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres fromXenopus laevis. 相似文献