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81.
Proteins and peptides in water-restricted environments 总被引:5,自引:0,他引:5
M Waks 《Proteins》1986,1(1):4-15
82.
The gibberellin (GA) 2-hydroxylases in mature and immature seeds of Pisum sativum have been partially purified and characterised. The enzymes are unstable when stored below pH 7.0 or in the absence of a thiol reagent. The optimum assay pH is between 7.4 and 7.8 and activity is dependent upon the presence of -ketoglutarate, Fe2+ and ascorbate. The 2-hydroxylase activities for GA1, GA4, GA9 and GA20 are chromatographically inseparable and correspond to a protein of Mr 44000. The rate of GA 2-hydroxylation varies according to substrate and some evidence indicates that the 2-hydroxylase activities for GA1 and GA4 and for GA9 and GA20 may reside in different proteins. During pea seed maturation, the specific activity of the enzyme(s) increases dramatically and reaches a maximum at a time when endogenous GA9, GA20, GA29 and GA51 are also at their greatest concentration. This correlation is not the result of substrate induction of enzyme activity. Since the GA 2-hydroxylases operate at maximal rate at low substrate concentrations they are incapable of rapidly 2-hydroxylating excessive quantities of (exogenously applied) GA1 or GA20. On the basis of the kinetic parameters of the GA 2-hydroxylase activities, a generalised model is discussed for the control of the steady-state levels of bioactive hormone under normal physiological conditions.Abbreviations DTE
dithioerythritol
- EDTA
ethylenediaminetetraacetic acid
- GAn
gibberellin An
- HPLC
high-performance liquid chromatography
- HSS
high-speed supernatant
- LSS
low-speed supernatant
- PMSF
phenylmethane sulphonyl fluoride 相似文献
83.
The effects of nine drugs on the CD spectra of a synthetic calcium binding analog of site III of rabbit skeletal troponin C, can generally be divided into 3 groups: (1) that consisting of haloperidol, benperidol, molindone and promethazine, had no effect on the CD spectrum or calcium sensitivity of the apopeptide; (2) that composed of structurally rigid thioxanthenes, induced CD-detectable structural change in the apopeptide but prevented Ca2+-induced structural change; (3) that consisting of chlorpromazine, trifluoperazine and fluphenazine, induced structural change in the peptide but had no effect on the Ca2+-induced structural change. 相似文献
84.
Bromo[1-14C]acetyl-CoA has been prepared from CoASH and the N-hydroxysuccinimide ester of bromo[1-14C]acetic acid, and unlabeled bromoacetyl-CoA by reaction of CoASH with bromoacetyl bromide. The products were purified by high-pressure liquid chromatography. Purified bromoacetyl-CoA was characterized, and found to be a potent alkylating agent with a substantial stability in aqueous solution: it decomposed at 30 degrees C and pH 6.6 and 8.0 with halftimes of 3.3 and 2.5 h, respectively. The major breakdown products were CoASH and CoAS X CO X CH2 X SCoA. Bromo[1-14C]acetyl-CoA has been used to affinity label the acetyl-CoA binding site of 3-hydroxy-3-methylglutaryl-CoA synthase from ox liver. It was found to irreversibly inhibit the enzyme activity and bind covalently with a stoichiometry for complete inhibition of about 0.8 mol/mol enzyme dimer. 相似文献
85.
Nedialka G. Markova George G. Markov 《Biochimica et Biophysica Acta (BBA) - Gene Structure and Expression》1983,741(1):7-14
Isopicnic centrifugation in Cs2SO4-Ag+ gradients at pH 7.0 reveals that the genome of the marine snail Rapana thomasiana Grosse (Gastropoda) contains an AT-rich satellite fraction comprising 5% of the DNA. Restriction enzyme analysis shows that the satellite DNA is composed of a number of related subsets arranged in tandem arrays. They have evolved from the segmental amplification of an 1460 bp long monomer unit with a complex inner organization. Most probably, the present basic repeat originates from an ancestral 400–500 bp long sequence in which some insertions and/or deletions have occurred. 相似文献
86.
Apparent unbalance between the activities of 6-phosphogluconate and glucose-6-phosphate dehydrogenases in rat liver 总被引:5,自引:0,他引:5
M Sapag-Hagar R Lagunas A Sols 《Biochemical and biophysical research communications》1973,50(1):179-185
The ratio of activities of 6-phosphogluconate dehydrogenase/glucose-6-phosphate dehydrogenase measured in liver extracts of rats in lipogenic nutritional conditions is only 0.2, suggesting an apparent physiological unbalance between the two dehydrogenases of the hexosemonophosphate shunt. This potential unbalance is enhanced by the fact that TPNH is a more powerful competitive inhibitor of 6-phosphogluconate dehydrogenase than of glucose-6-phosphate dehydrogenase. Accordingly, a strong activation of 6-phosphogluconate dehydrogenase would be required for efficient functioning of this pathway, unless there is an alternative outlet for 6-phosphogluconate so far unrecognized in animal tissues. 相似文献
87.
Glutamate dehydrogenase (GDH, E.C. 1.4.1.3) of mustard cotyledons was investigated during the first 4 days of seedling development. The enzyme was found to be composed of seven catalytically active isoforms (each with a molecular mass of 270 kDa) which exhibited a charge heterogeneity when investigated by isoelectric focusing. Antibodies against the purified isoform 7, raised in rabbits, cross-reacted with each of the isoforms in Western blotting experiments. In addition, each of the isoforms was composed of four immunopositive reacting polypeptides with 19, 21, 23 and 25 kDa. During development of the seedlings, a shift in the isoform pattern towards the more acidic forms was found which was more pronounced when the seedlings were supplied with 15 mM NH4Cl. The time course of changes in total GDH level can be correlated with the time course of disappearance of storage proteins. Both parameters are negatively regulated by light possibly via the photoreceptor, phytochrome. There are some indications that GDH in young mustard cotyledons mainly acts in the deaminating direction. 相似文献
88.
Ultrasensitive bioluminescence immunoassays for the determination of peptides and proteins (illustrated with human urinary kallikrein, bradykinin and the determination of human urinary kallikrein antibody titres) have been developed. The usable ranges of the standard curves are from 5 pg to 5000 pg per litre. The relative intra-assay coefficients of variation of the tests were between 2% and 6%, and the inter-assay coefficients of variation between 4% and 12%. 相似文献
89.
Study of the in vitro bioactivation of albendazole in human liver microsomes and hepatoma cell lines
Sylvie Rolin Hajar Souhaili-El Amri Anne-Marie Batt Michele Levy Denyse Bagrel Gerard Siest 《Cell biology and toxicology》1989,5(1):1-14
The metabolism of albendazole (ABZ), a benzimidazole anthelminthic, was studied in either microsomal preparations of human liver biopsies or cultured human hepatoma cell lines. Metabolites were analyzed by HPLC. Our data show that microsomes from human biopsies and two human cell lines, HepG2 and Hep3B, oxidize the drug to the sulfoxide very efficiently, whereas the third cell line tested, SK-HEP-1, does not. Both cytochrome P-450 dependent monooxygenases and favin-containing monooxygenases appear to be involved in human ABZ metabolism. Using the cell line displaying the highest ABZ-metabolizing activity, HepG2, the cytotoxic and the inducing effects of the parent drug ABZ and of two primary metabolites, the sulfoxide and the sulfone were studied. These three chemicals provoked a rise in mitotic index resulting from cell division blockage at the prophase or at the metaphase (ABZ metabolites) stage, and ABZ was more cytotoxic than its metabolites. With regard to enzyme-inducing effects, our data clearly demonstrate that the sulfoxide and, to a lesser degree, the sulfone are potent inducers of some drug metabolizing enzymes (i.e., cytochrome P-488 dependent monooxygenases and UDP glucuronyltransferase), whereas ABZ fails to increase and even slightly decreases these enzymatic activities. In conclusion, the HepG2 human hepatoma cell line appears to be suitable for the study of many parameters of metabolism and action of ABZ and other structurally related compounds in humans.Abbreviations ABZ
albendazole
- B[a]P
benzo[a]pyrene
- HPLC
high-performance liquid chromatography
- MC
3-methylcholanthrene
- MFO
mixed-function oxidase
- UDPGT
UDP-glucuronyltransferase 相似文献
90.
Joseph G. Major Jr. Melinda E. Wales John E. Houghton Julie A. Maley Jeffrey N. Davidson James R. Wild 《Journal of molecular evolution》1989,28(5):442-450
Summary Aspartate transcarbamoylase (ATCase, EC 2.1.3.2) is the first unique enzyme common to de novo pyrimidine biosynthesis and
is involved in a variety of structural patterns in different organisms. InEscherichia coli, ATCase is a functionally independent, oligomeric enzyme; in hamster, it is part of a trifunctional protein complex, designated
CAD, that includes the preceding and subsequent enzymes of the biosynthetic pathway (carbamoyl phosphate synthetase and dihydroorotase).
The complete complementary DNA (cDNA) nucleotide sequence of the ATCase-encoding portion of the hamster CAD gene is reported
here. A comparison of the deduced amino acid sequences of the hamster andE. coli catalytic peptides revealed an overall 44% amino acid similarity, substantial conservation of predicted secondary structure,
and complete conservation of all the amino acids implicated in the active site of theE. coli enzyme. These observations led to the construction of a functional hybrid ATCase formed by intragenic fusion based on the
known tertiary structure of the bacterial enzyme. In this fusion, the amino terminal half (the “polar domain”) of the fusion
protein was provided by a hamster ATCase cDNA subclone, and the carboxyl terminal portion (the “equatorial domain”) was derived
from a clonedpyrBI operon ofE. coli K-12. The recombinant plasmid bearing the hybrid ATCase was shown to satisfy growth requirements of transformedE. coli pyrB
− cells. The functionality of thisE. coli-hamster hybrid enzyme confirms conservation of essential structure-function relationships between evolutionarily distant
and structurally divergent ATCases. 相似文献