Nucleosides. CXIX. Substrate specificity and mechanism of action of cytidine deaminases of monkey plasma and mouse kidney

Abstract The in vitro properties of semi-purified chlorophyllase (chlorophyll-chlorophyllido hydrolase, EC 3.1.1.14) from Capsicum annuum fruits have been studied. The enzym e showed an optimum of activity at pH 8.5 and 50 °C. Substrate specificity was studied for chlorophyll (Chi) a, Chi b, pheophytin (Phe) a and Phe b, with Km values of 10.70, 4.04, 2.67 and 6.37 μᴍ respectively. Substrate inhibition was found for Phe b at concentrations higher than 5 μᴍ. Chlorophyllase action on Chi a' and Chi b' was also studied but no hydrolysis was observed, suggesting that the mechanism of action depends on the configuration at C-132 in the chloro phyll molecule, with the enzyme acting only on compounds with R132 stereochemistry. The effect of various metals (Mg2+, Hg2+, Cu2+, Zn2+, Co , Fe2+ and Fe3+) was also investigated, and a general inhibitory effect was found, this being more marked for Hg2+ and Fe2+. Functional groups such as -SH and -S-S-seem ed to participate in the formation o f the enzyme-substrate complex. Chelating ion and the carbonyl group at C3 appeared to be important in substrate recognition by the enzyme. The method for measuring Chlase activity, including HPLC separation of substrate and product, has been optimized.

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Micrococcus luteus endonucleases for apurinic/apyrimidinic sites in deoxyribonucleic acid. 2. Further studies on the substrate specificity and mechanism of action

Biochemistry ◽

10.1021/bi00563a014 ◽

1980 ◽

Vol 19 (22) ◽

pp. 5024-5029 ◽

Cited By ~ 16

Author(s):

Josiane Pierre ◽

Jacques Laval

Keyword(s):

Substrate Specificity ◽

Mechanism Of Action ◽

Deoxyribonucleic Acid ◽

Micrococcus Luteus

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Cytoplasmic initiation of cisplatin cytotoxicity

AJP Renal Physiology ◽

10.1152/ajprenal.00593.2007 ◽

2008 ◽

Vol 295 (1) ◽

pp. F44-F52 ◽

Cited By ~ 60

Author(s):

Fang Yu ◽

Judit Megyesi ◽

Peter M. Price

Keyword(s):

Cell Death ◽

Mechanism Of Action ◽

Cultured Cells ◽

Chemotherapeutic Agent ◽

Protective Action ◽

Mouse Kidney ◽

Proximal Tubule Cells ◽

Cell Death Pathway ◽

Cdk2 Activity ◽

Localization Signal

The mechanism of action of cisplatin as a chemotherapeutic agent has been attributed to DNA binding, while its mechanism of action as a nephrotoxin is unresolved. Only ∼1% of intracellular cisplatin interacts with DNA, primarily forming intrastrand cross-linked adducts, and many studies have implicated both nuclear and cytoplasmic causes of cisplatin-induced death in cultured cells. We have demonstrated that cisplatin cytotoxicity depends on cdk2 activity, which is at least partly through the cdk2-E2F1 pathway. The mechanism of the dependency on cdk2, and whether cdk2 activation of E2F1 represents the only cell death pathway involved, is still unclear. Our previous work showed that deletion of the nuclear localization signal from p21WAF1/CIP1, a cdk2 inhibitor, did not alter its protective action against cisplatin cytotoxicity. Active cdk2-cyclin complexes are localized in both the nucleus and cytoplasm, and it was reported that cdk2 translocated to the cytoplasm after an apoptotic stimulus. Herein, we show that cisplatin caused cell death in enucleated mouse kidney proximal tubule cells (TKPTS), which was prevented by cdk2 inhibition. Also, we localized cytoplasmic cdk2 to both the endoplasmic reticulum (ER) and Golgi compartments, and ER stress was blocked by specific cdk2 inhibition. We conclude that cisplatin can induce nuclear independent apoptosis, cisplatin cytotoxicity can be initiated by cytoplasmic events, and cytoplasmic cdk2 plays an important role in apoptosis signaling.

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A STUDY OF THE ANDROGEN RECEPTORS IN A VARIETY OF ANDROGEN-SENSITIVE TISSUES

Journal of Endocrinology ◽

10.1677/joe.0.0590121 ◽

1973 ◽

Vol 59 (1) ◽

pp. 121-139 ◽

Cited By ~ 102

Author(s):

W. I. P. MAINWARING ◽

F. R. MANGAN

Keyword(s):

Mechanism Of Action ◽

Binding Proteins ◽

Early Growth ◽

Mouse Kidney ◽

Biochemical Effects ◽

Nuclear Extracts ◽

Sexual Glands ◽

Androgenic Steroids ◽

Low Activity

SUMMARY A search has been conducted for specific, 5α-dihydrotestosterone-binding proteins in a wide variety of tissues and cells upon which androgenic steroids have pronounced morphological and biochemical effects. High affinity binding proteins of this nature have been identified in cytoplasmic and nuclear extracts from a diversity of accessory sexual glands of many species, mouse kidney, testis and certain experimental androgen-dependent tumours. They are notably absent in most types of skeletal muscle and in soluble extracts prepared from prokaryotic organisms. The implications of these findings to the mechanism of action of androgenic steroids are discussed. While the selective binding of 5α-dihydrotestosterone indubitably plays a role of paramount importance in the mechanism of action of androgens in many accessory sexual glands throughout life, this process may be of importance in other tissues only during the period of early growth and development. A severe limitation to the importance of the binding of 5α-dihydrotestosterone in certain adult tissues is imposed by the very low activity of the enzyme, 5α-reductase, responsible for the formation of 5α-dihydrotestosterone.

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