Effects of some drugs on human erythrocyte 6-phosphogluconate dehydrogenase: an in vitro study

Inhibitory effects of some drugs were investigated on human erythrocyte 6-phosphogluconate dehydrogenase obtained with a 6552-fold purification in a yield of 78% using 2′, 5′-ADP Separose 4B affinity gel. Which on SDS polyacrylamide gel electrophoresis showed a single band. Larnoxicam, metronidazole, imipenem, ornidazole, vancomycin, clindamycin, and amoxicillin exhibited inhibitory effects on the enzyme in vitro with IC₅₀ values of 0.17, 0.23, 0.43, 21.79, 46.39, 117.43 and 287.35 mM, and the Ki constants 0.40 ± 0.04, 0.57 ± 0.06, 0.77 ± 0.11, 42.40 ± 2.89, 65.60 ± 4.03, 130.22 ± 9.21, and 287.58 ± 10.56 mM, respectively. While vancomycin, clindamycin and amoxicillin showed competitive inhibition the other drugs displayed noncompetitive inhibition.     

Effects of some antibiotics on human erythrocyte glutathione reductase: an in vitro study

Inhibitory effects of some antibiotics on purified human erythrocyte glutathione reductase were investigated. Human erythrocyte glutathione reductase was purified 2800-fold (29% yield) at 4 degrees C using 2', 5'-ADP Sepharose 4B affinity gel and Sephadex G-200 gel filtration chromatography. SDS polyacrylamide gel electrophoresis showed a single band for the enzyme. Imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol, seftriaxon, vancomycin, cefuroxime and ornidazole exhibited inhibitory effects but clindamycin, lincomycin, amoxicillin, amikacin exhibited activatory effects on the enzyme in vitro. The IC(50) values of imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol, seftriaxon, vancomycin, cefuroxime and ornidazole were 0.030, 0.146, 0.59, 2.476, 2.36, 2.88, 4.83, 15.43 and 19.632 mM, respectively, and the K(i) constants were 0.06 +/- 0.01, 0.275 +/- 0.10, 0.85 +/- 0.05, 3.59 +/- 0.51, 3.85 +/- 0.40, 3.71 +/- 0.60, 15.11 +/- 2.50, 23.50 +/- 2.94 and 28.49 +/- 6.50 mM, respectively. While imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol and seftriaxon cefuroxime and ornidazole showed competitive inhibition, vankomycine displayed noncompetitive inhibition.     

Effects of some antibiotics on human erythrocyte glutathione reductase: an in vitro study

Inhibitory effects of some antibiotics on purified human erythrocyte glutathione reductase were investigated. Human erythrocyte glutathione reductase was purified 2800-fold (29% yield) at 4°C using 2′, 5′-ADP Sepharose 4B affinity gel and Sephadex G-200 gel filtration chromatography. SDS polyacrylamide gel electrophoresis showed a single band for the enzyme. Imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol, seftriaxon, vancomycin, cefuroxime and ornidazole exhibited inhibitory effects but clindamycin, lincomycin, amoxicillin, amikacin exhibited activatory effects on the enzyme in vitro. The IC₅₀ values of imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol, seftriaxon, vancomycin, cefuroxime and ornidazole were 0.030, 0.146, 0.59, 2.476, 2.36, 2.88, 4.83, 15.43 and 19.632 mM, respectively, and the K_i constants were 0.06 ± 0.01, 0.275 ± 0.10, 0.85 ± 0.05, 3.59 ± 0.51, 3.85 ± 0.40, 3.71 ± 0.60, 15.11 ± 2.50, 23.50 ± 2.94 and 28.49 ± 6.50 mM, respectively. While imipenem, rifamycin, sulfanylacetamide, ceftazidime, chloramphenicol and seftriaxon cefuroxime and ornidazole showed competitive inhibition, vankomycine displayed noncompetitive inhibition.     

Effects of some drugs on the activity of glucose 6-phosphate dehydrogenase from rainbow trout (Oncorhynchus mykiss) erythrocytes in vitro

Inhibitory effects of some drugs on glucose 6-phosphate dehydrogenase from the erythrocytes of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) were investigated. The enzyme was purified 2488-fold in a yield of 76.8% using ammonium sulfate precipitation and 2',5'-ADP Sepharose 4B affinity gel at 4 degrees C. The drugs pental sodium, MgSO4, vancomycin, metamizol, marcaine, and prilocaine all exhibited inhibitory effects on the enzyme. While MgSO4 (K(i) = 12.119 mM), vancomycin (K(i) = 1.466 mM) and metamizol (K(i) = 0.392 mM) showed competitive inhibition, pental sodium (K(i) = 0.748 mM) and marcaine (K(i) = 0.0446 mM) displayed noncompetitive inhibition.     

Effects of some drugs on the activity of glucose 6-phosphate dehydrogenase from rainbow trout (Oncorhynchus mykiss) erythrocytes in vitro

Inhibitory effects of some drugs on glucose 6-phosphate dehydrogenase from the erythrocytes of rainbow trout (Oncorhynchus mykiss Walbaum, 1792) were investigated. The enzyme was purified 2488-fold in a yield of 76.8% using ammonium sulfate precipitation and 2′,5′-ADP Sepharose 4B affinity gel at 4°C. The drugs pental sodium, MgSO₄, vancomycin, metamizol, marcaine, and prilocaine all exhibited inhibitory effects on the enzyme. While MgSO₄ (K_i = 12.119 mM), vancomycin (K_i = 1.466 mM) and metamizol (K_i = 0.392 mM) showed competitive inhibition, pental sodium (K_i = 0.748 mM) and marcaine (K_i = 0.0446 mM) displayed noncompetitive inhibition.     

Effects of some analgesic anaesthetic drugs on human erythrocyte glutathione reductase: an in vitro study

Inhibitory effects of some analgesic and anaesthetic drugs on human erythrocyte glutathione reductase were investigated. For this purpose, human erythrocyte glutathione reductase was initially purified 2139-fold in a yield of 29% by using 2', 5'-ADP Sepharose 4B affinity gel and Sephadex G-200 gel filtration chromatography. SDS polyacrylamide gel electrophoresis confirmed the purity of the enzyme by sharing a single band. A constant temperature (+4 degrees C) was maintained during the purification process. Diclofenac sodium, ketoprofen, lornoxicam, tenoxicam, etomidate, morphine and propofol exhibited inhibitory effects on the enzyme in vitro using the Beutler assay method. K(i) constants and IC(50) values for drugs were determined from Lineweaver-Burk graphs and plotting activity % versus [I] graphs, respectively. The IC(50) values of diclofenac sodium, ketoprofen, lornoxicam, propofol, tenoxicam, etomidate and morphine were 7.265, 6.278, 0.3, 0.242, 0.082, 0.0523 and 0.0128 mM and the K(i) constants were 23.97 +/- 2.1, 22.14 +/- 7.6, 0.42 +/- 0.18, 0.418 +/- 0.056, 0.13 +/- 0.025, 0.0725 +/- 0.0029 and 0.0165 +/- 0.0013 mM, respectively. While diclofenac sodium, ketoprofen, lornoxicam, tenoxicam etomidate and morphine showed competitive inhibition, propofol displayed noncompetitive inhibition.     

Effects of some metal ions on human erythrocyte glutathione reductase: an in vitro study

In this study, we investigated inhibitory effects of some metal ions on human erythrocyte glutathione reductase. For this purpose, initially human erythrocyte glutathione reductase was purified 1051-fold in a yield of 41% by using 2', 5'-ADP Sepharose 4B affinity gel and Sephadex G-200 gel filtration chromatography. SDS polyacrylamide gel electrophoresis was done in order to control the purification of enzyme. SDS polyacrylamide gel electrophoresis showed a single band for enzyme. A constant temperature (4 degrees C) was maintained during the purification process. Enzyme activity was determined with the Beutler method by using a spectrophotometer at 340 nm. Hg(2+), Cd(2+), Pb(2+), Cu(2+), Fe(3+) and Al3+ exhibited inhibitory effects on the enzyme in vitro. K(i) constants and IC(50) values for metal ions were determined by Lineweaver-Burk graphs and plotting activity % vs. [I]. IC(50) values of Pb(2+), Hg(2+), Cu(2+), Cd(2+), Fe(3+) and Al(3+) were 0.011, 0.020, 0.0252, 0.0373, 0.209 and 0.229 mM, and the Ki constants 0.0254+/-0.0027, 0.0378+/-0.0043, 0.0409+/-0.0048, 0.0558+/-0.0083, 0.403+/-0.043 and 1.137+/-0.2 mM, respectively. While Pb(2+), Hg(2+), Cd(2+) and Fe(3+) showed competitive inhibition, others displayed noncompetitive inhibition.     

Inhibitory effects of ofloxacin and cefepime on enzyme activity of 6-phosphogluconate dehydrogenase from chicken liver

In this study, effects of some antibiotics, namely, ofloxacin, cefepime, cefazolin, and ampicillin on the in vitro enzyme activity of 6-phosphogluconate dehydrogenase have been investigated. For this purpose, 6-phosphogluconate dehydrogenase was purified from chicken liver 535-fold with a yield of 18% by using ammonium sulphate precipitation, 2',5'-ADP Sepharose 4B affinity chromatography, and Sephadex G-200 gel filtration chromatography. In order to check the purity of the enzyme, SDS polyacylamide gel electrophoresis (SDS-PAGE) was performed. This analysis revealed a highly pure enzyme band on the gel. Among the antibiotics, ofloxacin and cefepime exhibited inhibitory effects, but cefazolin and ampicillin showed neither important inhibitory nor activatory effects on the enzyme activity. The measured I(50) values by plotting activity percent vs. inhibitor concentration, [I(50)] were 0.1713 mM for ofloxacin and 6.0028 mM for cefepime. Inhibition constants, K(i), for ofloxacin and cefepime were also calculated as 0.2740 +/- 0.1080 mM and 12.869 +/- 16.6540 mM by means of Lineweaver-Burk graphs, and inhibition types of the antibiotics were found out to be non-competitive and competitive, respectively. It has been understood from the calculated inhibitory parameters that the purified chicken enzyme has been quite inhibited by these two antimicrobials.     

In vitro effects of some antibiotics on glutathione reductase from sheep liver

The effects of gentamicin sulphate, thiamphenicol, ofloxacin, levofloxacin, cefepime, and cefazolin were investigated on the in vitro enzyme activity of glutathione reductase. The enzyme was purified 1,850-fold with a yield 18.76% from sheep liver using ammonium sulphate precipitation, 2',5'-ADP Sepharose 4B affinity chromatography, and Sephadex G-200 gel filtration chromatography. The purified enzyme showed a single band on sodium dodecyl sulfate polyacrilamide gel electrophoresis (SDS-PAGE). The enzyme activity was measured spectrophotometrically at 340 nm, according to the method of Carlberg and Mannervik. From these six antibiotics, Ofloxacin, levofloxacin, cefepime, and cefazolin inhibited the activity of the purified enzyme; gentamicin sulphate and thiamphenicol showed little effect on the enzyme activity. The I50 values for these four antibiotics were 0.150 mM, 0.154 mM, 3.395 mM, and 18.629 mM, respectively. The Ki constants were 0.047 +/- 0.034 mM, 0.066 +/- 0.038 mM, 4.885 +/- 3.624 mM, and 6.511 +/- 1.894 mM, respectively and they were competitive inhibitors.     

In vitro effects of some anaesthetic drugs on lactoperoxidase enzyme activity

In vitro effects of ketamine and bupivacaine drugs on bovine lactoperoxidase (LPO; E.C. 1.11.1.7) enzyme activity were investigated. Lactoperoxidase was purified with Amberlite CG 50 resin, CM Sephadex C-50 ion-exchange chromatography, and Sephadex G-100 gel filtration chromatography from skimmed bovine milk. Rz(A412/A280) value for the purified LPO was found to be 0.8. Inhibition or activation effects of the drugs on LPO enzyme were determined using 2,2(1)-azino-bis (3-ethylbenzthiazoline-6 sulfonic acid) diammonium salt (ABTS) as a chromogenic substrate at pH = 6.0. The I50 values of ketamine and bupivacaine were 0.29 mM and 0.155 mM, respectively and the K(i) constants for ketamine and bupivacaine were 0.019 +/- 0.031 and 0.015 +/- 0.021 mM, respectively; they were non-competitive inhibitors.     

Inhibition of L-arginine iminohydrolase (EC 3.5.3.6) from Tetrahymena thermophila by putrescine and spermidine: feedback control of polyamine biosynthesis

L-Arginine iminohydrolase (arginine deiminase, ADI) from Tetrahymena thermophila was purified approx. 75-fold by means of gel permeation chromatography. The Km of the purified enzyme for L-arginine was 412 +/- 25 microM and L-ornithine inhibited the reaction competitively with a Ki of 985 +/- 105 microM. D-Ornithine was a weak inhibitor with a Ki of greater than 10mM. The polyamines putrescine and spermidine inhibited ADI incompetitively with a Kii of 2.8mM for putrescine and 4.3mM for spermidine. Since the concentrations required for inhibition were within the range of the normal intracellular polyamine concentrations in Tetrahymena (maximally 14mM putrescine and 4mM spermidine), it is suggested that the polyamine effects on ADI are of regulatory nature. Thus, polyamine biosynthesis in Tetrahymena thermophila is regulated not only on the level of ornithine decarboxylase activity, but also on an earlier step, the supply of ODC with substrates.     

Urate excretion by the isolated perfused rat kidney and modification by drugs

Urate excretion in the isolated perfused rat kidney was studied over a wide range of perfusate urate concentrations (13.9-376.8 microM). Fractional excretion of urate (FEurate) averaged 57.9 +/- 2.0% (range, 58.5-59.6%), showed marked interanimal variability, but was not dependent on the perfusate-free urate concentration. In paired experiments, the effects of five drugs (probenecid, pyrazinoate, furosemide, salicylate, and oxonate) on FEurate were evaluated. A low concentration of pyrazinoate (0.2 mM) decreased FEurate (62.0 +/- 1.9 vs 53.8 +/- 2.4%, P less than 0.05), as did 0.8 mM pyrazinoate (59.5 +/- 2.4 vs 48.4 +/- 2.7%, P less than 0.05). Probenecid (1 mM) decreased FEurate (59.3 +/- 3.1 vs 52.0 +/- 2.5%, P less than 0.05) but 2.5 mM probenecid did not alter FEurate (48.0 +/- 6.3 vs 47.8 +/- 6.9%). Oxonate (0.1 mM) also decreased FEurate (75.8 +/- 4.2 vs 67.1 +/- 2.1%, P less than 0.05) while 0.2 mM oxonate had no effect (66.4 +/- 3.5 vs 61.5 +/- 4.6%). Neither salicylate nor furosemide affected FEurate, although both drugs caused a saliuresis and diuresis. Thus, urate transport in rat kidneys in vitro is not dependent on urate concentration, unlike man. Some drugs known to affect urate excretion in humans and rats did not have similar effects in isolated kidneys. Isolated organ studies provide additional information is understanding renal urate handling.     

Susceptibility of Genital Mycoplasmas to Antimicrobial Agents

The susceptibility of 11 T-strains, 12 strains of Mycoplasma hominis, and a single strain of M. fermentans to 15 antimicrobial agents was determined by study of inhibition of metabolic activity in a broth dilution system. All three species were inhibited by tetracycline, chloramphenicol, streptomycin, gentamicin, and kanamycin, and were relatively resistant to cephalothin, cephaloridine, polymyxin, vancomycin, and ampicillin. Three antimicrobial agents had significant differential effects on these species. Erythromycin was more active against T-strains than against M. hominis or M. fermentans. Lincomycin, clindamycin, and nitrofurantoin had greater activity against M. hominis and M. fermentans than against T-strains. The activity of the drugs tested was generally uniform over a wide range of inocula. The effect of pH and the difference between minimal inhibiting and minimal mycoplasmacidal concentrations of the drugs tested were consistent with expectations based on the effects of these drugs on bacteria.     

Novel purification strategy for human PON1 and inhibition of the activity by cephalosporin and aminoglikozide derived antibiotics

Human serum paraoxonase (PON1, EC 3.1.8.1.) is a high-density lipid (HDL)-associated, calcium-dependent enzyme; its physiological substrates are not known. In this study, a new purification strategy for human PON1 enzyme was developed using two-step procedures, namely ammonium sulfate precipitation and sepharose-4B-l-tyrosine-1-napthylamine hydrophobic interaction chromatography. SDS-polyacrylamide gel electrophoresis of the enzyme indicates a single band with an apparent MW of 43 kDa. Overall purification rate of our method was found 227-fold. The V(max) and K(m) of the purified enzyme were determined 227.27 EU and 4.16 mM, respectively. The in vitro effects of commonly used antibiotics, namely gentamycin sulfate and cefazolin sodium was also investigated on the purified human serum PON1 enzyme and human liver PON1 enzyme from human hepatoma cell (HepG2). Gentamycin sulfate and cefazolin sodium caused a dose- and time-dependent decrease on PON1 activity in HepG2 cells. Moreover, gentamycin sulfate and cefazolin sodium were effective inhibitors on purified human serum PON1 activity with IC(50) of 0.887 and 0.0084 values, respectively. The kinetics of interaction of gentamycin sulfate and cefazolin sodium with the purified human serum PON1 indicated a different inhibition pattern. Cefazolin sodium showed a competitive inhibition with K(i) of 0.012+/-0.00065 mM. However, Gentamycin sulfate was inhibited in non-competitive manner with K(i) of 0.026+/-0.015. In order to determine the inhibition statue of these drugs on a living system, the effects of same antibiotics on PON1 enzyme activity of mouse serum PON1 and liver PON1 were investigated in vivo. Gentamycin sulfate (3.2 mg/kg) and cefazolin sodium (106.25 mg/kg) leads to the significant decrease in mouse serum PON1 after 2, 4, 6 h and 2, 4 h drug administration, respectively. Cefazolin sodium did not exhibit any inhibition effect for the liver PON1, in vivo.     

Investigation of the effects of some sulfonamide derivatives on the activities of glucose-6-phosphate dehydrogenase, 6-phospho gluconate dehydrogenase and glutathione reductase from human erythrocytes

In this study, the in vitro effects of some sulfonamide derivatives, which are carbonic anhydrase inhibitors, on the enzymes activities of glucose-6-phosphate dehydrogenase, 6-phospho gluconate dehydrogenase and glutathione reductase were investigated. For this purpose, these three enzymes were purified from human erythrocytes. Purification procedure composed of four steps; preparation of the hemolysate, ammonium sulfate precipitation, 2',5'-ADP Sepharose 4B affinity chromatography, and gel filtration chromatography on Sephadex G-200. 5-(3alpha-Hydroxy-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (1), 5-(3alpha,12alpha-Dihydroxy-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (2), 5-(3alpha,7alpha,12alpha-Trihydroxy-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (3), 5-(3alpha,Acetoxy-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (4), 5-(3alpha,7alpha,12alpha-Triacetoxy-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (5), 5-(3,7,12-Trioxo-5-beta-cholanamido)-1,3,4-thiadiazole-2-sulfonamide (6), acetazolamide, and dorzolamide were tested in this experiment. Compounds 3, 5, and dorzolamide showed inhibitory effects on the activity of 6-phosphogluconate dehydrogenase, and I(50) values and K(i) constants were calculated as 0.0601 mM, 0.00253 mM, and 1.41 mM and 0.0878 +/- 0.0274 mM, 0.0042 +/- 0.0009 mM, and 3.1446 +/- 0.2081 mM, respectively. Glutathione reductase was also inhibited by 1 and 2. I(50) values and K(i) constants were 0.0471 mM and 0.0723 +/- 0.0388 mM for 1 and 0.0045 mM and 0.0061 +/- 0.0014 mM, for 2. If these sulfonamide derivatives are proposed as drugs, some of which are being used in glaucoma treatment such as acetazolamide and dorzolamide, these results should be taken into consideration concerning via these enzymes.     

医院感染葡萄球菌的耐药性及D-试验研究分析

目的了解医院感染葡萄球菌的耐药性及克林霉素诱导试验（D-试验）临床意义。方法从住院患者标本中分离到的539株葡萄球菌进行药敏试验和D-试验,所得结果进行统计分析。结果葡萄球菌中耐甲氧西林金黄色葡萄球菌（MRSA）和耐甲氧西林凝固酶阴性葡萄球菌（MPSE）的检出率高,分别为65．1％和83．6％,各种葡萄球菌对万古霉素敏感率为100％,对阿奠西林头孢菌素在内的各种β-内酰胺酶类抗生素敏感率低于35％,对红霉素耐克林霉素敏感的D-试验阳性率为57．O％。结论葡萄球菌耐甲氧西林检出率,呈多重耐药,在选用大环内酯类,克林霉素类抗生素时要注意D试验,合理用药,提高疗效。     

Mechanisms of inhibition of phenylalanine ammonia-lyase by phenol inhibitors and phenol/glycine synergistic inhibitors

Phenylalanine ammonia-lyase (PAL) catalyzes the beta-elimination of ammonia from L-phenylalanine to trans-cinnamic acid. A study of inhibition of PAL by phenol, ortho-cresol, and meta-cresol gave mixed inhibition; para-cresol is not an inhibitor. The calculated values of K(i) and alphaK(i) are phenol, K(i)=2.1+/-0.5 mM and alphaK(i)=3.45+/-0.95 mM; ortho-cresol, K(i)=0.8+/-0.2 mM and alphaK(i)=3.4+/-0.2 mM; meta-cresol, K(i)=2.85+/-0.15 mM and alphaK(i)=18.5+/-1.5 mM. The synergistic inhibition of the same inhibitors with glycine showed a lack of inhibition with the para-cresol/glycine pair, while mixed inhibition was observed with the ortho-cresol/glycine pair (K(i)=0.038+/-0.008 mM, alphaK(i)=0.13+/-0.04 mM) and phenol/glycine pair (K(i)=0.014+/-0.003 mM, alphaK(i)=0.058+/-0.01 M). The meta-cresol/glycine pair gave competitive inhibition (K(i)=0.36+/-0.076 mM). The strong synergistic inhibition observed implies that the inhibitors bind at the active site: in fact, the inhibitors used imitate the structure of the substrate. The order of synergistic inhibition is the same for the sites related to K(i) and alphaK(i). These results are in agreement with the inhibitors entering two active sites located in two different subunits.     

Thionamides and arsenite inhibit specific T3 binding to the hepatic nuclear receptor

Methimazole (MMI) and propylthiouracil (PTU) are widely used for the treatment of Graves' disease. However, no studies have been reported on the action of these drugs on binding of L-triiodothyronine (T3) to the nuclear receptor. T3 receptors of rat liver nuclei, prepared by differential centrifugation, were extracted with 0.4 M KCl and 5 mM dithiothreitol (DTT). In the assessment of T3 binding to the DTT-reduced receptor, the hepatic nuclear extract was chromatographed on Superose 6 to remove DTT and isolate proteins of relative mass approximately 50,000 (chromatographed nuclear receptors (CNRs)), prior to the addition of [125I]T3 of high specific activity (3300 microCi/micrograms; 1 Ci = 37 GBq). MMI or PTU at 2 mM reduced specific T3 binding to CNR by 84% and 85%, respectively. The inhibitory effects of these reagents and 2 mM sodium arsenite (which complexes dithiols) were additive. Scatchard analyses indicated that neither MMI nor PTU (at 2 mM) significantly altered the affinity constant (Ka) (from 2.41 x 10(9) to 1.74 x 10(9) M-1 for PTU and 1.79 x 10(9) M-1 for MMI), while they both decreased (p less than 0.02) maximal binding capacity (from 0.36 +/- 0.02 to 0.19 +/- 0.02 pmol/mg protein for MMI and 0.17 +/- 0.02 pmol/mg protein for PTU). Dose-response curves showed that 50% inhibition was attained at 0.6 mM PTU or 1.0 mM MMI with approximately 25% inhibition by both at 0.1 mM. Artefactual binding effects by MMI and PTU on [125I]T3 were excluded by chromatography experiments. Similar results were obtained using nuclear receptors prepared from livers of hyperthyroid rats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of some antibiotics on glutathione reductase activities from human erythrocytes in vitro and from rat erythrocytes in vivo

The effects of streptomycin sulfate, gentamicin sulfate, thiamphenicol, penicillin G, teicoplanin, ampicillin, cefotaxime, and cefodizime on the enzyme activity of glutathione reductase (GR) were studied using human and rat erythrocyte GR enzymes in in vitro and in vivo studies, respectively. The enzyme was purified 5,342-fold from human erythrocytes in a yield of 29% with 50.75 U/mg. The purification procedure involved the preparation of hemolysate, ammonium sulfate precipitation, 2',5'-ADP Sepharose 4B affinity chromatography and Sephadex G-200 gel filtration chromatography. Purified enzyme was used in the in vitro studies, and rat erythrocyte hemolysate was used in the in vivo studies. In the in vitro studies, I50 and K(i) values were 12.179 mM and 6.5123 +/- 4.1139 mM for cefotaxime, and 1.682 mM and 0.7446 +/- 0.2216 mM for cefodizime, respectively, showing the inhibition effects on the purified enzyme. Inhibition types were noncompetitive for cefotaxime and competitive for cefodizime. In the in vivo studies, 300 mg/kg cefotaxime and 1000 mg/kg cefodizime when administered to rats inhibited enzyme activity during the first 2h (p < 0.01). Cefotaxime led to increased enzyme activity at 4h (p < 0.05), but neither cefotaxime nor cefodizime had any significant inhibition or activation effects over 6 h (p > 0.05).     

Interaction of the antibiotics clindamycin and lincomycin with Escherichia coli 23S ribosomal RNA.

Interaction of the antibiotics clindamycin and lincomycin with Escherichia coli ribosomes has been compared by chemical footprinting. The protection afforded by both drugs is limited to the peptidyl transferase loop of 23S rRNA. Under conditions of stoichiometric binding at 1 mM drug concentration in vitro, both drugs strongly protect 23S rRNA bases A2058 and A2451 from dimethyl sulphate and G2505 from kethoxal modification; G2061 is also weakly protected from kethoxal. The modification patterns differ in that A2059 is additionally protected by clindamycin but not by lincomycin. The affinity of the two drugs for the ribosome, estimated by footprinting, is approximately the same, giving Kdiss values of 5 microM for lincomycin and 8 microM for clindamycin. The results show that in vitro the drugs are equally potent in blocking their ribosomal target site. Their inhibitory effects on peptide bond formation could, however, be subtly different.