Effects of repeated +Gz exposures on lipid peroxidation of various organs in rats

OBJECTIVE

To investigate the change of lipid peroxidation in various organs of rats after repeated +10 Gz stress.

METHOD

Twenty male Wistar rats were randomly divided into control (+1 Gz) group and +10 Gz group (n = 10 for each group ). The two groups were exposed to +1 Gz or +10 Gz on an animal centrifuge respectively. The onset rate of +Gz was 0.5 G/s; the sustained time at peak +Gz was 30 s each time, with 5 times/d, 1 min intervals, 3 d/wk, 3 wk in total. The rats were decapitated in ice bath on the next day after the last +Gz exposure. The lung, heart, liver and kidney of rats were collected for the following determinations. These organs were made into homogenates and the mitochondria of heart and kidney were isolated from their homogenates. Then malondialdehyde (MDA) content , superoxide dismutase (SOD) activity and glutathion (GSH) concentration in these homogenates and mitochondria were determined individually.

RESULT

Compared with the control, MDA concentration in myocardial mitochondria increased significantly (P < 0.01) after repeated +10 Gz exposures, and the SOD activity in liver homogenate and renal mitochondria decreased remarkably (P < 0. 01). But there was no significant difference between GSH concentrations of the two groups.

CONCLUSION

Repeated +10 Gz stress induced lipid peroxidation injury of myocardial mitochondria and had some influences on the oxygen radical metabolism of liver and kidney in rats.

Removal and recovery of chromium(III) from aqueous solutions by a spheroidal cellulose adsorbent

The removal and recovery of chromium(III) (Cr3+) from aqueous solutions with a spheroidal cellulose adsorbent containing the carboxyl anionic group was investigated. The adsorption of Cr3+ ion on the adsorbent has been found to be time, concentration, pH, and temperature dependent. The adsorption process follows both the Freundlich and Langmuir adsorption isotherms, and has been found to be endothermic (enthalpy change, deltaH = 31.35 kJ/mol). The Cr3+ ion adsorbed on the adsorbent can be recovered by treating with a sodium hydroxide (NaOH) or hydrochloric acid (HCl) solution in one of two methods, static desorption or mobile desorption (column operation). A 1.2 mol/L HCl aqueous solution was finally chosen to recover the Cr3+ ion using column operation. The recovery percentage is approximately 85.2%. The exhausted column can be chemically regenerated by treatment with 1 mol/L NaOH aqueous solution and no dismantling is required. The adsorption mechanism is explained on the basis of complexation and ion exchange, between which the complexation adsorption is predominant.

Protective effects of tea polyphenols on mild hypobaric hypoxia induced pulmonary free radical metabolic disorder in mice

Objective. To observe the protective effects of natural antioxidant tea polyphenols (TP) on repeated mild hypobaric hypoxia induced pulmonary free radical metabolic disorder in mice. Method. Fourty-two male Kunming mice were randomly divided into three groups (n=14 each): normal control (A); 1500 in mild hypobaric hypoxia (B) and TP protection group (C). The exposure time in hypobaric chamber was 2 h/d, 3d/wk, 8 wk in total. Before hypoxic exposure, TP was orally given to group C at a dose of 100 mg/kg, while distilled water was given to the other two groups. After experiment, the mice were decapitated on the next day and the lung was quickly removed. The malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity and nitric oxide (NO) content were measured. In addition, Cu, Zn-SOD and inducible NO synthase (iNOS) enzymatic contents in lung were were qualitatively examined by immunohistochemical assaying. Result. Compared with the control group, pulmonary MDA concentration and NO content were significantly increased after chronic mild hypobaric hypoxic exposures (P<0.01) but the MDA formation and NO generation in TP protection group were restored to normal. Pulmonary SOD activity in group B tended to increase. Cu, Zn-SOD expression in endothelial cells of bronchioli and iNOS contents in endothelial cells of bronchioli and endothelial cells and smooth muscle cells in pulmonary interstitial vessels were significantly elevated after repeated mild hypobaric hypoxic exposure. These enzymatic abnormal expressions regained to normal after administration of TP. Conclusion. Natural antioxidant TP had protective effects on repeated mild hypobaric hypoxia induced pulmonary free radical metabolic disorder.

[Sequences of 5S-rRNA gene spacer region and comparison of alkaloid content in Fritillaria thunbergii from different habitats]

OBJECTIVE

To study the genetic basis of the formation of indigenous Chinese medicine materials.

METHODS

The 5S-rRNA gene spacer regions in F. thunbergii from different habitats were amplified with AS and AS-1 as primers, and then sequenced. Total alkaloid contents were assayed by acid dye colorimetry, and 2 main alkaloid contents were assayed by pre-column derivatization and gas chromatographic method.

RESULT

The sequenues of 5S-rRNA gene spacer regions in F. thunbergii from different habitats were same, and the length of them was 588 bp. They had same content total alkaloid. The results of gas chromatography showed that they had same kinds of monomer alkaloids, but the contents of different monomer alkaloids were different.

CONCLUSION

The difference of alkaloid content in F. thunbergii from various habitats isn't resulted from base sequence variation, but from microenvironment.

[Inhibitory effects of tea polyphenols and vitamin C on lipid peroxidation induced by FeSO4- cysteine in isolated human plasma and carbon tetrachloride-induced liver free radical injury in mice]

OBJECTIVE

To investigate the inhibitory effects of tea polyphenols (TP) and Vitamin C (Vit C) on FeSO4-cysteine induced lipid peroxidation in isolated human plasma and carbon tetrachloride (CCl4) induced liver free radical injury in mice.

METHOD

The experiment included two parts: (1) In FeSO4-cysteine induced lipid peroxidation system of isolated human plasma, malondialdehyde (MDA) content was detected after administration of different concentrations of TP (0.3 ~ 8.1 mg/L, as C ~ F group) and Vit C (3 ~ 81 mg/L, as G ~ J group) respectively; (2) Thirty-six male Kunming mice were randomly divided into four groups: control group (A), CCl4 damage group (B), TP protection group (C) and Vit C protection group (D). TP or Vit C (100 mg/kg) was given orally to group C and D respectively, while the same volume of distilled water was given to the other two groups one time every day, continued for three days. Twelve hours after the final treatment, CCl4 (230 mg/kg) was given orally to group B ~ D. Thirty six hours later, all the mice were decapitated and liver homogenate were prepared for measuring MDA content.

RESULT

In FeSO4-cysteine induced lipid peroxidation in isolated human plasma, the inhibitory rate of TP (0.3 ~ 8.1 mg/L) was 30.7%, 32.0%, 46.9% and 59.7 %, and the inhibitory rate of Vit C (3 ~ 8.1 mg/L) was 8.3%, 41.4%, 47.7% and 52.7% for various dosages. In the CCl4 induced liver free radical injury system, the inhibitory rate of the same dosage of TP and Vit C was 45.2%, 42.8% respectively.

CONCLUSION

TP (0.3 ~ 8.1 mg/L) and Vit C (9 ~ 81 mg/L) had inhibited lipid peroxidation induced by FeSO4-cysteine in isolated human plasma significantly, and the inhibitory effects of TP was superior to that of Vit C at the same dosages. The same dosage of TP and Vit C had remarkable inhibitory effects on the CCl4 induced liver free radical injury, but there was no significant difference between the two groups.

Protective effects of tea polyphenols on myocardial free radical metabolic disorder in mice induced by inhalation of pure oxygen under 5500 m hypobaric condition

OBJECTIVE

To observe the protective effects of natural antioxidant tea polyphenols(TP) on myocardial free radical metabolic disorder in mice induced by inhalation of hypobaric pure oxygen under 5500 m hypobaric condition.

METHOD

Forty-two male Kunming mice were randomly divided into three groups (n = 14 each): group A, normal control; group B, inhalation of pure oxygen (> 96 %) at simulated altitude of 5500 m in an animal altitude chamber; group C (TP protection group), same as group B but 100 mg/kg of TP was given orally before the exposure. The exposure time was 2 h/d, 3 d/wk for a total of 8 wk, and distilled water was given to groups A and B before exposure. After experiment, the mice were decapitated on the next day and the heart was quickly removed. Malondialdehyde (MDA) concentration, superoxide dismutase (SOD) activity and nitric oxide (NO) content were measured. In addition, Cu, Zn-SOD and inducible NO synthase (iNOS) enzymatic contents in myocardial tissue were qualitatively examined by immunohistochemical assaying.

RESULT

Compared with the control, MDA concentration, SOD activity and Cu, Zn-SOD enzymatic content in group B were significantly increased (P < 0. 05). But in TP protection group, myocardial MDA formation was significantly decreased (P < 0. 01) and SOD activity and Cu, Zn-SOD expression restored to normal. On the contrary, myocardial NO generation and iNOS expression were significantly reduced after repeated inhalation of hypobaric oxygen at 5500 m. NO metabolism regained to normal after repeated administration of TP.

CONCLUSION

Natural antioxidant TP had protective effects on myocardial free radical metabolic disorder induced by inhalation of hypobaric pure oxygen under 5500 m hypobaric condition.

Expression, purification, and characterization of deglycosylated human pro-prostate-specific antigen

Wild-type and deglycosylated forms of human prostate-specific antigen were expressed in Chinese hamster ovary (CHO) cells as zymogens. ProPSA was collected from conditioned medium and purified using a single cation-exchange chromatographic step for the deglycosylated form and cation-exchange followed by gel filtration chromatography for the wild-type form. Recombinant wild-type proPSA produced in CHO cells has an average MW of 34.5 kDa, whereas the deglycosylated proPSA has a MW of 32.4 kDa. Both forms of proPSA were activated in vitro and the kinetic properties measured for the deglycosylated PSA are very similar to those of the wild-type recombinant PSA and the native PSA isolated from seminal fluid. These results suggest that deglycosylated PSA is likely to be very similar to native PSA with respect to its three-dimensional structure and will provide a homogeneous protein preparation necessary for X-ray crystallographic analysis.

Crystal structure of human cathepsin V

Cathepsin V is a lysosomal cysteine protease that is expressed in the thymus, testis and corneal epithelium. We have determined the 1.6 A resolution crystal structure of human cathepsin V associated with an irreversible vinyl sulfone inhibitor. The fold of this enzyme is similar to the fold adopted by other members of the papain superfamily of cysteine proteases. This study provides a framework for understanding the structural basis for cathepsin V's activity and will aid in the design of inhibitors of this enzyme. A comparison of cathepsin V's active site with the active sites of related proteases revealed a number of differences, especially in the S2 and S3 subsites, that could be exploited in identifying specific cathepsin V inhibitors or in identifying inhibitors of other cysteine proteases that would be selective against cathepsin V.

[Effects of simulated flight hypobaric hypoxia and oxygen inhalation on free radical metabolism in various organs of mice]

Objective. To investigate the effects of two types of simulated flight conditions (hypobaric hypoxia and hypobaric oxygen inhalation) on free radical metabolism in various organs of mice. Method. Sixty male Kunming mice were randomly divided into six groups (n=10 each). The experiment comprises two parts. The first part included three groups: normal controls (A1), 1500 m hypobaric hypoxia for 4 wk (B1) and 8 wk (C1). The second part included another three groups: normal control (A2), 5500 m hypobaric oxygen inhalation for 4 wk (B2) and 8 wk (C2). The exposure time in hypobaric chamber was 2 h/d, 3 d/wk. After experiment, caudal blood was taken for routine examination. The mice were decapitated on the next day and brain, heart, lung, liver and kidney homogenates were prepared for measuring malondialdehyde (MDA) content and superoxide dismutase (SOD) activity. Result. Lipid peroxides in lung was significantly increased in C1 group, and the content of myocardial MDA and myocardial SOD activities in C2 group were markedly higher than those in A2 group. There were no significant differences among body weights, mean corpuscular indices and hemoglobin content in the normal control, hypobaric hypoxia and hypobaric oxygen inhalation groups. It demonstrates that repeated mild hypobaric hypoxia for 8 wk causes free radical damage of lung and repeated exposure to 5500 m hypobaric oxygen inhalation for 8 wk may lead to myocardial peroxidative injury in mice. Conclusion. Simulated flight hypobaric hypoxia and oxygen inhalation may lead to free radicals damage of lung and myocardial peroxidative injury in mice.

[Effects of tea polyphenols on microcirculation and antioxidation in aircrew]

OBJECTIVE

To study the effects of tea polyphenols (TP) on bulbi conjunctiva microcirculation (BCM) and antioxidation in aircrew and find out the proper antioxidant for the health protection of aircrew.

METHOD

Fourty healthy aircrew were divided into TP group (TP 600 mg/d.po) and control group (placebo) randomly. The effects of TP on microcirculation and antioxidation in aircrew were tested after 20 days.

RESULT

Red blood cell (RBC) superoxide dismutase (SOD) activity and GSH-PX (Whole blood glutathione peroxidase)/MDA (serum malondialdehyde) ratio in TP group were significantly higher than those in control (P<0.01), and serum MDA level was significantly decreased after TP administration (P<0.05). The numbers of capillaries and blood flow in micrangium were significantly increased, RBC aggregation, ischemia area and A (arteriole)/V (venule) ratio were remarkably decreased in TP group (P<0.01). The total integral value of microcirculation in TP group was significantly reduced in comparison with that in the control group.

CONCLUSION

TP can significantly increase the antioxidative ability of aircrew, decrease the BCM disturbance and improve the microcirculatory function.

A method for quick measurement of protein binding to unilamellar vesicles

A general method for measuring interaction of liposome-protein (or potentially small molecules) was developed. This method utilizes biotinylated liposomes to incubate with interactants. Streptavidin-coated paramagnetic resins were then added and the liposomes (along with bound materials) can be quickly separated under a magnetic field or by low speed centrifugation. Subsequently, concentration of unbound materials (in the supernatants) can be directly determined. The described method is particularly useful for proteins or compounds that are not very soluble under certain assay conditions.

Conformation of the diphtheria toxin T domain in membranes: a site-directed spin-labeling study of the TH8 helix and TL5 loop

The isolated T domain of diphtheria toxin was mutated by cysteine-scanning mutagenesis at 28 consecutive sites (residues 328-355) that comprise the TH8 helix and the TL5 interhelical loop in the native toxin. After derivatizing the mutant proteins with a sulfhydryl-selective nitroxide reagent, we examined the mobility of each nitroxide and its accessibility to polar and nonpolar paramagnetic reagents, before and after insertion into phospholipid bilayers. The data obtained with the proteins in solution at pH 8 are generally consistent with predictions from the crystal structure of the toxin. Upon membrane binding at pH 4.6, a major structural reorganization of the domain was seen, which dramatically reduced the accessibility of most residues in this region to the polar reagent nickel(II)-ethylenediaminediacetate complex (NiEDDA). Many of these residues also showed reduced accessibility to the nonpolar reagent O(2). Periodic accessibility of the nitroxide side chains along the sequence to these reagents shows that TH8 remains largely helical in the membrane-bound state, with one surface associated with protein and the other facing the hydrophobic interior of the bilayer. In addition, the TL5 loop also appears to become alpha-helical in the membrane, with one surface in contact with protein and the other in contact with the bilayer interior. These findings provide a structural framework for understanding how the T domain forms a transmembrane channel and mediates translocation of diphtheria toxin's enzymic moiety across a membrane.

Engineering a soluble extracellular erythropoietin receptor (EPObp) in Pichia pastoris to eliminate microheterogeneity, and its complex with erythropoietin

The extracellular ligand-binding domain (EPObp) of the human EPO receptor (EPOR) was expressed both in CHO (Chinese Hamster Ovary) cells and in Pichia pastoris. The CHO and yeast expressed receptors showed identical affinity for EPO binding. Expression levels in P. pastoris were significantly higher, favoring its use as an expression and scale-up production system. Incubation of EPO with a fourfold molar excess of receptor at high protein concentrations yielded stable EPO-EPObp complexes. Quantification of EPO and EPObp in the complex yielded a molar ratio of one EPO molecule to two receptor molecules. Residues that are responsible for EPOR glycosylation and isomerization in Pichia were identified and eliminated by site-specific mutagenesis. A thiol modification was identified and a method was developed to remove the modified species from EPObp. EPObp was complexed with erythropoietin (EPO) and purified. The complex crystallized in two crystal forms that diffracted to 2.8 and 1.9 A respectively. (Form 1 and form 2 crystals were independently obtained at AxyS Pharmaceuticals, Inc. and Amgen, Inc. respectively.) Both contained one complex per asymmetric unit with a stoichiometry of two EPObps to one EPO.

Effects of tea polyphenols on cardiac function and myocardial ultrastructure in rats after repeated +Gz stress

Objective. To observe the effects of tea polyphenols (TP) on cardiac function and myocardial ultrastructure in rats after repeated +10 Gz stress. Method. Twenty four male Wistar rats were randomly divided into three groups (n=8 each): group A (control), group B (+10 Gz), group C (+Gz with TP). Group B and C were repeatedly exposed to +10 Gz (each for 30 s, onset rate about 0.5 G/s, 3 times/d with +1 Gz 1 min intervals, 3 d/wk, 4 weeks in total), but group A was only submitted to +1 Gz. TP (200 mg kg-1) was given orally to group C about 1 h prior to the +Gz experiment, and distilled water was given to group A and B. Function of isolated rat working hearts and myocardial ultrastructure were observed. Result. A significant decrease of left ventricular systolic pressure (LVSP) and injury of myocardial structure in rats were demonstrated after repeated +10 Gz stress. But TP could remarkably elevate the LVSP and improve myocardial ultrastructural injury in +10 Gz stressed rats. Conclusion. These results indicated that repeated high G exposure may produce cardiac structural and functional injuries in rats which might be partly related to free radical metabolism; and antioxidant TP had significant protective effects on the hearts of +Gz stressed rats.

[Experimental study on carotid artery resection with vascular replacement by an autogenous vein graft]

OBJECTIVE

In order to observe the survival rate and the histologic changes of the reestablished common carotid artery system.

METHOD

A planned resection of the carotid artery was done and the common carotid artery system was reestablished by interposing an autogenous external jugular vein graft in 15 white rabbits.

RESULT

12 survived, the other 3 rabbits died from graft thrombosis, the survival rate was 80%. Histologic examination demonstrated the smooth internal tunic in the anastomotic part of the carotid-jugular and no graft thrombosis. Angiography demonstrated the free circulation of the blood and no aneurysm in the anastomotic vein.

CONCLUSION

It is concluded that it is possible that in selected patients, a planned resection of the carotid artery with replacement by interposing an autogenous external jugular vein graft will be done.

Effects of tea polyphenols on cerebral lipid peroxidation, liver and renal functions in rats after repeated +Gz stress

OBJECTIVE

To observe the effects of repeated +10 Gz stress on cerebral lipid peroxidation, liver and renal function in rats and the prophylactic effects of antioxidant tea polyphenols (TP).

METHOD

Twenty-four male Wistar rats were randomly divided into three groups (n = 8, each): group A (control), group B (+10 Gz), and group C (TP). Group B and C were exposed to repeated +10 Gz stress (each for 30s, onset rate about 0.5 G/s, 3 times/d with +1 Gz 1 min intervals, 3 d/wk, 4 weeks in total), but group A was only submitted to +1 Gz. TP (200 mg/kg) was given orally in group C about 1 h prior to the +Gz experiment, while distilled water was given in group A and B. Lipid peroxidation in the brain, liver and renal functions and serum lipids were determined.

RESULTS

As compared with the control, lipid peroxidation in rat cerebral homogenate, mitochondria and cytoplasm was significantly increased (P < 0. 05), and serum creatinine concentration was markedly elevated after repeated +10 Gz stress (P < 0. 01). But, TP had significant inhibitory effect on +10 Gz stress induced peroxidative injury in rat brain and reduced the serum creatinine level. There were no differences of serum triglyceride and total cholesterol concentrations and glutamic-pyruvic transaminase activity among the three groups.

CONCLUSION

These results indicated that repeated high +Gz stress could bring about peroxidative injury in brain and harmful effect on renal function, and natural antioxidant TP had significant protective effects.

Effects of mutations in proline 345 on insertion of diphtheria toxin into model membranes

Translocation of the catalytic domain of diphtheria toxin (DT) across the endosomal membrane to the cytoplasm of mammalian cells requires the low-pH-dependent insertion of a hydrophobic helical hairpin (TH8-TH9) that is buried within the T domain of the native protein. Mutations of Pro345, which terminates helix TH8, have been reported to block toxicity for Vero cells. We found that mutant toxins in which Pro345 had been replaced by Cys, Glu, or Gly were profoundly defective at low pH in forming channels in planar phospholipid bilayers and in permeabilizing phospholipid vesicles to entrapped fluorophores. Experiments with isolated T domain containing a polarity-sensitive fluorophore attached to Cys at position 332 suggest that the P345E mutation blocks membrane insertion. None of the Pro345 mutations shifted the pH-dependence of binding in solution of the hydrophobic fluorophore, 2-p-toluidinyl-naphthalene 7-sulfonate. The results indicate that proline at position 345 is required for the T domain to insert into phospholipid bilayers or to adopt a functional conformation within the bilayer.

[Isozyme electrophoresis of Fritillaria puqiensis during bulb organogenesis in vitro]

OBJECTIVE

Inquiring into the mechanism of bulb organogenesis of Fritillaria puqiensis.

METHOD

Time course studies of the soluble protein, peroxidase and esterase were performed during the new bulb organogenesis by electrophoresis.

RESULT

The atlas of electrophoresis changed greatly during the phase of differentiation and the formation of the new bulb.

CONCLUSION

Different enzymes are associated with organogenesis and express activity at different times.

Efficiency of signalling through cytokine receptors depends critically on receptor orientation

Human erythropoietin is a haematopoietic cytokine required for the differentiation and proliferation of precursor cells into red blood cells. It activates cells by binding and orientating two cell-surface erythropoietin receptors (EPORs) which trigger an intracellular phosphorylation cascade. The half-maximal response in a cellular proliferation assay is evoked at an erythropoietin concentration of 10 pM, 10(-2) of its Kd value for erythropoietin-EPOR binding site 1 (Kd approximately equal to nM), and 10(-5) of the Kd for erythropoietin-EPOR binding site 2 (Kd approximately equal to 1 microM). Overall half-maximal binding (IC50) of cell-surface receptors is produced with approximately 0.18 nM erythropoietin, indicating that only approximately 6% of the receptors would be bound in the presence of 10 pM erythropoietin. Other effective erythropoietin-mimetic ligands that dimerize receptors can evoke the same cellular responses but much less efficiently, requiring concentrations close to their Kd values (approximately 0.1 microM). The crystal structure of erythropoietin complexed to the extracellular ligand-binding domains of the erythropoietin receptor, determined at 1.9 A from two crystal forms, shows that erythropoietin imposes a unique 120 degrees angular relationship and orientation that is responsible for optimal signalling through intracellular kinase pathways.

Expression of active thrombopoietin and identification of its key residues responsible for receptor binding

In this report expression of the biologically active N-terminal half (amino acids 1-153) of thrombopoietin (TPO153) in Escherichia coli is described and the structure-function relationships in TPO are explored. TPO153 was chosen for expression because of its full biological activity. Since natural TPO153 cDNA expressed poorly, synthetic cDNA was constructed with a unique polymerase chain reaction to enhance the expression. In addition, the 5'-end codons of the synthetic cDNA were altered to maximize the expression. The expressed TPO153 was refolded and then purified to homogeneity. The protein is biologically active, and interestingly, the EC50 of this protein is 8-10-fold smaller in a TPO-dependent cell proliferation assay than that of full-length wild-type TPO. In order to identify the amino acid residues that are involved in the interaction between TPO and its receptor, all charged residues and some of the uncharged residues on the four putative helices of TPO were mutated and biological activities of the mutant proteins were examined. The mutagenesis studies suggest that there are at least two clusters of residues that are vital for TPO to be able to interact with its receptor. These residues are centred respectively around arginine 10 on helix 1 and around lysine 138 on helix IV. The successful expression of the protein in E. coli will greatly facilitate biochemical and crystallographic studies of TPO, and the structure-function relationship studies suggest that TPO has two binding sites which may interact with two individual receptors, resulting in dimerization of the receptors.

Identification of shallow and deep membrane-penetrating forms of diphtheria toxin T domain that are regulated by protein concentration and bilayer width

The alpha-helix-rich, hydrophobic transmembrane (T) domain of diphtheria toxin is believed to play a central role in membrane insertion by the toxin and in the translocation of its catalytic domain across membranes. In this report, T domain structure was studied using site-directed single-Cys mutants. The residues chosen, 322 (near the amino-terminal end of helix TH8), 333 (within helix TH8), and 356 (within helix TH9) were substituted with Cys and labeled with the fluorescent probe bimane. (Residues 333 and 356 should be located within the bilayer in the transmembrane state, and residue 322 should not penetrate the bilayer.) After insertion of T domain into model membrane vesicles, the location of bimane label relative to the lipid bilayer was characterized by its fluorescence emission and by its quenching with nitroxide-labeled phospholipids. It was found that when the T domain is added to dioleoylphosphatidylcholine-containing vesicles, all three residues reside close to the outer surface. However, at high T domain concentration or in thinner dimyristoleoylphosphatidylcholine-containing vesicles, a large fraction of residues 333 and 356 penetrate deeply into the membrane. In contrast, residue 322 remains exposed to aqueous solution under these conditions. These conclusions were confirmed by a novel antibody binding method. Antibodies that quench the fluorescence of 4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-3-indacene++ + (BODIPY) groups were used to evaluate the exposure of BODIPY-labeled 322, 333, and 356. Maximum exposure of residues 333 and 356 to externally added antibody was only observed under conditions in which bimane fluorescence showed that these residues do not penetrate the bilayer. In contrast, residue 322 remained exposed under all conditions. We propose that the deeply penetrating T domain conformation represents a transmembrane or near-transmembrane state. The regulation of the transmembrane/nontransmembrane equilibrium should be a key to understanding diphtheria toxin membrane insertion and translocation. Our results suggest that toxin-toxin interactions may play an important role in regulating this behavior.

Probing the structure of the diphtheria toxin channel. Reactivity in planar lipid bilayer membranes of cysteine-substituted mutant channels with methanethiosulfonate derivatives

Previous work has established that the 61 amino acid stretch from residue 322 to 382 in the T-domain of diphtheria toxin forms channels indistinguishable in ion-conducting properties from those formed by the entire T-domain. In the crystal structure of the toxin's water-soluble form, the bulk of this stretch is an alpha-helical hairpin, designated TH8-9. The present study was directed at determining which residues in TH8-9 line the ion-conducting pathway of the channel; i.e., its lumen or entrances. To this end, we singly mutated 49 of TH8-9's 51 residues (328-376) to cysteines, formed channels with the mutant T-domain proteins in planar lipid bilayers, and then determined whether they reacted with small, charged, lipid-insoluble, sulfhydryl-specific methanethiosulfonate (MTS) derivatives added to the bathing solutions. The indication of a reaction, and that the residue lined the ion-conducting pathway, was a sudden change in single-channel conductance and/or flickering behavior. The results of this study were surprising in two respects. First, of the 49 cysteine-substituted residues in TH8-9 tested, 23 reacted with MTS derivatives in a most unusual pattern consisting of two segments: one extending from 329 to 341 (11 of 13 reacted), and the other from 347 to 359 (12 of 13 reacted); none of the residues outside of these two segments appeared to react. Second, in every cysteine mutant channel manifesting an MTS effect, only one transition in single-channel conductance (or flickering behavior) occurred, not the several expected for a multimeric channel. Our results are not consistent with an alpha-helical or beta-strand model for the channel, but instead suggest an open, flexible structure. Moreover, contrary to common sense, they indicate that the channel is not multimeric but is formed from only one TH8-9 unit of the T-domain.

Characterization of the receptor binding determinants of granulocyte colony stimulating factor

We performed a series of experiments using alanine-scanning mutagenesis to locate side chains within human granulocyte colony-stimulating factor (G-CSF) that are involved in human G-CSF receptor binding. We constructed a panel of 28 alanine mutants that examined all surface exposed residues on helices A and D, as well as all charged residues on the surface of G-CSF. The G-CSF mutants were expressed in a transiently transfected mammalian cell line and quantitated by a sensitive biosensor method. We measured the activity of mutant proteins using an in vitro proliferation assay and an ELISA binding competition assay. These studies show that there is a region of five charged residues on helices A and C employed by G-CSF in binding its receptor, with the most important residue in this binding patch being Glu 19. Both wild-type G-CSF and the E19A mutant were expressed in E. coli. The re-folded proteins were found to have proliferative activities similar to the analogous proteins from mammalian cells: furthermore, biophysical analysis indicated that the E19A mutation does not cause gross structural perturbations in G-CSF. Although G-CSF is likely to signal through receptor homo-dimerization, we found no compelling evidence for a second receptor binding region. We also found no evidence of self-antagonism at high G-CSF concentrations, suggesting that, in contrast to human growth hormone (hGH) and erythropoietin (EPO), G-CSF probably does not signal via a pure 2:1 receptor ligand complex. Thus, G-CSF, while having a similar tertiary structure to hGH and EPO, uses different areas of the four helix bundle for high-affinity interaction with its receptor.

Homodimerization of erythropoietin receptor by a bivalent monoclonal antibody triggers cell proliferation and differentiation of erythroid precursors

Erythropoietin (EPO) stimulates proliferation and differentiation of erythroid progenitor cells. Several lines of evidence indicate that the most likely mechanism of EPO receptor (EPO-R) activation by EPO is homodimerization of the receptor on the surface of erythrocyte precursors. Therefore, we argued that it should be possible to raise EPO-R monoclonal antibodies (MoAbs) that would activate the receptor by dimerization and thus mimic EPO action. We have identified such an agonist MoAb (MoAb34) directed against the extracellular EPO binding domain of the EPO-R. This bivalent IgG antibody triggers the proliferation of EPO-dependent cell lines and induces differentiation of erythroid precursors in vitro. In contrast, the monovalent Fab fragment, which cannot dimerize the receptor, is completely inactive. The mechanism of receptor activation by homodimerization implies that at high ligand concentrations the formation of 1:1 receptor/ligand complexes is favored over 2:1 complexes, thereby turning the ligand agonist into an antagonist. Thus, EPO and MoAb34 should self-antagonize at high concentrations in both cell proliferation and differentiation assays. Our data indeed demonstrate that EPO and MoAb34 antagonize ligand-dependent cell proliferation with IC50 values of approximately 20 and 2 mumol/L, respectively. Erythroid colony formation (BFUe) is inhibited at MoAb34 concentrations above 1 mumol/L. Furthermore, we analyzed the MoAb34:EPO-R interaction using a mathematic model describing antibody-mediated receptor dimerization. The data for proliferation and differentiation activity were consistent with the receptor dimer formation on the cell surface predicted by the model.

Organization of diphtheria toxin T domain in bilayers: a site-directed spin labeling study

The diphtheria toxin transmembrane (T) domain was spin-labeled at consecutive residues in a helical segment, TH9. After binding of the T domain to membranes at low pH, the nitroxide side chains generated by spin labeling were measured with respect to their frequency of collision with polar and nonpolar reagents. The data showed that the helical structure of TH9 in solution is conserved, with one face exposed to water and the other to the hydrophobic interior of the bilayer. Measurement of the depth of the nitroxide side chains from the membrane surfaces revealed an incremental change of about 5 angstroms per turn, which is consistent with a transmembrane orientation of an alpha helix. These results indicate that the helix forms the lining of a transmembrane water-filled channel.

Interaction of the isolated transmembrane domain of diphtheria toxin with membranes

Insertion of diphtheria toxin's T (transmembrane) domain into the endosomal membrane under acidic conditions is known to promote translocation of its catalytic domain across the membrane and into the cytosol. The T domain, a cysteine-free bundle of alpha-helices, was expressed as a discrete protein in Escherichia coli and purified. The isolated domain was stable and largely monomeric at pH 8.0. Like the holotoxin it bound the hydrophobic fluorophore, 2-p-toluidinylnaphthalene 6-sulfonate, upon acidification, but the transition pH was higher than with the holotoxin (pH 5.6 vs 5.1) and broader, reflecting the absence of interdomain interactions. The domain also permeabilized large unilamellar vesicles under acidic conditions, as demonstrated by release of entrapped solutes. Mutant forms of T domain, each with a single residue replaced by cysteine, were derivatized with a thiol-reactive nitroxide-containing spin label and analyzed by electron paramagnetic resonance (EPR). EPR spectra and solvent accessibilities of the labels at pH 8.0 were consistent with the environments predicted from the toxin's crystallographic structure. Acidification in the presence of large unilamellar vesicles caused a nitroxide label at position 332 on helix TH8 to move from a buried site in the water soluble state to a lipid-exposed surface site at a depth of approximately 15 A within the bilayer. This is consistent with the concept that the TH8-TH9 helix pair inserts into the bilayer.(ABSTRACT TRUNCATED AT 250 WORDS)

Dynamic transitions of the transmembrane domain of diphtheria toxin: disulfide trapping and fluorescence proximity studies

Translocation of the catalytic domain of diphtheria toxin across the endosomal membrane to the cytosolic compartment depends on low-pH-triggered insertion of the toxin's T (transmembrane) domain into the membrane. The T domain, consisting of nine alpha-helices arranged in three layers, was cloned and expressed as a discrete protein in Escherichia coli, and mutant forms were prepared and characterized. To investigate the relative movements of the three layers under various conditions, we generated two mutant forms of the domain, each containing an artificial intramolecular disulfide bridge linking the buried apolar hairpin (TH8-TH9) to one of the other two layers. Both disulfides inhibited exposure of the domain's apolar regions in solution at low pH, as determined by 2-p-toluidinylnaphthalene-6-sulfonate binding, and blocked its ability to form channels in artificial bilayers. Reduction of the bridges abolished these effects. Reduced forms of the mutant proteins were reacted with pyrenylmaleimide, a fluorescent probe, to monitor separation of the layers. Strong excimer bands seen in both mutants at neutral pH were undiminished at pH 5, indicating the retention of gross conformation in solution under acidic conditions. The addition of phospholipid vesicles at pH 5, but not at pH 7.5, quenched excimer fluorescence, reflecting the physical separation of the TH8-TH9 hairpin from the other layers upon the T domain's interaction with the bilayer. The results indicate that (i) the conformation of the isolated T domain closely resembles that seen in the whole toxin, (ii) the TH8-TH9 hairpin separates from both of the other layers of the domain as an essential step of membrane insertion, and (iii) this separation is triggered by contact of the domain with the membrane under acidic conditions.

Reaction of diphtheria toxin channels with sulfhydryl-specific reagents: observation of chemical reactions at the single molecule level

The diphtheria toxin channel is believed to be a homooligomer of its T domain in which each subunit consists of two alpha-helices, lying within the membrane, connected by a short interhelical loop of four amino acids (residues 349-352). To investigate the validity and implications of this model, we singly mutated each of these amino acids to cysteines, formed channels with the mutant T-domain proteins in planar lipid bilayers, and added to the trans compartment sulfhydryl-specific reagents [methanethiosulfonate derivatives (MTS-ER)] that introduce a positive or negative charge to reacted cysteines. The introduction of a positive charge at residue 351 or 352 (through the MTS-ER reactions) resulted in a step decrease in single-channel conductance, whereas the introduction of a negative charge resulted in a step increase. The opposite sign of these effects indicates the predominantly electrostatic nature of the phenomenon and implies that residues 351 and 352 lie close to the channel entrance. The same reactions at residue 350 resulted in very little change in channel conductance but instead changed the character of the natural rapid flickering of the channel between open and closed states to one in which the channel spent more time in the closed state; this may have resulted from the group introduced at position 350 acting as a tethered channel blocker. The MTS derivatives had no effect on channels containing a cysteine at position 349, suggesting that this residue faces away from the channel entrance. We propose that the step changes in conductance or flickering pattern result from the chemical reaction of one MTS-ER molecule with one cysteine, and thus a bimolecular chemical reaction is being witnessed at the single molecule level. From the distribution of waiting times between the appearance (i.e., the opening) of a channel and the step change in its conductance or flickering pattern, we can calculate a pseudo-first-order rate constant, which can then be converted to a second-order rate constant, for the chemical reaction.

Modulation by beta-aminopropionitrile of vessel luminal narrowing and structural abnormalities in arterial wall collagen in a rabbit model of conventional balloon angioplasty versus laser balloon angioplasty

This study was designed to assess the potential relationship between the late loss of angiographic luminal diameter and biochemical abnormalities of arterial wall collagen in rabbits subjected to angioplasty, and to test the hypothesis that beta-aminopropionitrile (beta APN), an inhibitor of lysyl oxidase, would inhibit such changes when administered orally for 1 mo after angioplasty. Endovascular injury was induced in rabbit iliac arteries by ipsilateral balloon angioplasty (BA) and by contralateral balloon angioplasty accompanied by exposure to continuous wave neodymium: yttrium aluminum garnet laser radiation (LBA). Computer measurement of angiographic luminal diameter demonstrated significant vessel narrowing at 1 and 6 mo after both procedures. By quantitative histology, the majority of the 1-mo loss in angiographic diameter could not be attributed to neointimal thickening. Analysis of collagen cross-linking by HPLC in collagen obtained from the LBA-injured segments of the arteries 1 mo after angioplasty revealed a significant increase, relative to values from uninjured arteries (P < 0.05), in the difunctional cross-link dihydroxylysinonorleucine (DHLNL). 6 mo after angioplasty, the content of hydroxypyridinium, the trifunctional maturational product of DHLNL, was significantly elevated in both BA- and LBA-treated arteries compared with values from uninjured arteries (P < 0.05). In animals administered beta APN, luminal narrowing at 1 mo, compared with controls, was attenuated (P < 0.01) and DHLNL content was decreased (P < 0.05) in arteries subjected to LBA, but not in arteries subjected to BA. The results suggest that lathyrogenic agents may be efficacious in favorably modulating LBA-induced alterations in vessel diameter and mural connective tissue.

Structure-function relationships in diphtheria toxin channels: I. Determining a minimal channel-forming domain

Diphtheria Toxin (DT) is a 535 amino acid exotoxin, whose active form consists of two polypeptide chains linked by an interchain disulphide bond. DT's N-terminal A fragment kills cells by enzymatically inactivating their protein synthetic machinery; its C-terminal B chain is required for the binding of toxin to sensitive cells and for the translocation of the A fragment into the cytosol. This B fragment, consisting of its N-terminal T domain (amino acids 191-386) and its C-terminal R domain (amino acids 387-535) is responsible for the ion-conducting channels formed by DT in lipid bilayers and cellular plasma membranes. To further delineate the channel-forming region of DT, we studied channels formed by deletion mutants of DT in lipid bilayer membranes under several pH conditions. Channels formed by mutants containing only the T domain (i.e., lacking the A fragment and/or the R domain), as well as those formed by mutants replacing the R domain with Interleukin-2 (IL-2), have single channel conductances and selectivities essentially identical to those of channels formed by wild-type DT. Furthermore, deleting the N-terminal 118 amino acids of the T domain also has minimal effect on the single channel conductance and selectivity of the mutant channels. Together, these data identify a 61 amino acid stretch of the T domain, corresponding to the region which includes alpha-helices TH8 and TH9 in the crystal structure of DT, as the channel-forming region of the toxin.

Effects of thermal exposure on binding of heparin in vitro to the arterial wall and to clot and on the chronic angiographic luminal response to local application of a heparin film during angioplasty in an in vivo rabbit model

Experimentally, heparin inhibits mechanisms that promote fibrosis, neointimal cellular proliferation, and thrombin bound to fibrin at the surface of intraluminal thrombus, but only in relatively high concentrations. A preliminary hypothesis was tested and confirmed in vitro that initial binding of 3H-heparin to mechanically injured porcine aorta is concentration-dependent over a 1,000-50,000 units/ml range (r = 0.9). The hypothesis was then tested in vitro that thermal exposure during contact of heparin to arterial tissue and to clot would enhance binding of the drug. 3H-heparin binding to clot, whole blood particulates, and washed erythrocytes was markedly enhanced by exposure to temperatures > 70 degrees C. Thermal exposure (80 degrees C x 40 s) also enhanced tissue persistence of the drug within porcine aorta subjected to a shear rate of 1,100(-1) in an annular Baumgartner chamber perfused with normal saline at 37 degrees C for 48 h. Heparin in vitro anticoagulant activity persisted after thermal exposure and binding to tissues. A new method was developed for local application of a heparin film that provides a maximum concentration with a tolerable systemic dose during an angioplasty procedure. In an in vivo rabbit model of mural fibrosis after iliac artery angioplasty, the 1-month mean angiographic luminal diameter loss (23% compared to the acute postangioplasty result by computer image analysis) in response to conventional balloon angioplasty (BA) and laser balloon angioplasty (LBA) was the same (P > 0.05). Local application of a heparin film (3,000 units at a concentration > 100,000 units/g), however, reduced the mean % loss in diameter 1 month after LBA (12%), but not after BA (29%), compared to arteries subjected to angioplasty without local heparin (P < .05). The results are consistent with the hypothesis that thermal energy enhances heparin binding to tissues and that local application of a heparin film favorably modulates arterial luminal responses to LBA, but not to BA, in this animal model.

Erythrocyte haemolysate interacts with ATP-Fe to form a complex containing iron, ATP and 13 800 MW polypeptide

Iron first entering the reticulocyte is bound to ATP in the low MW cytosolic pool; some is also 'loosely bound' to haemoglobin, coeluting with haemoglobin from a molecular sieve column though not incorporated into haem. When haemolysate is mixed with ATP-Fe in vitro a similar high MW iron-containing complex is formed: the ATP-Fe interacts with a non-haemoglobin constituent of the haemolysate to form a high MW ATP-Fe complex in which the ratio of ATP:Fe (originally 6:1) is reversed, so that the complex contains more iron than ATP. The high MW ATP-Fe complex is formed even when ATP is in 150-fold molar excess and is formed without detectable hydrolysis of the ATP. The activity of haemolysate in forming the high MW ATP-Fe complex is not diminished by dialysis; all of the activity is recovered in the haemoglobin-containing fraction obtained from an Ultrogel AcA 44 column. The activity does not derive from haemoglobin since 85% of the activity is removed when haemoglobin is purified from haemolysate with DEAE-Sephadex. The chelatable iron pool of the cell probably includes both the high MW ATP-Fe complex and low MW ATP-Fe. Shunting of ATP-Fe to a high MW aggregate reduces the amount of iron present in the highly reactive low MW form and thus probably serves to limit the formation of cell damaging radicals.

Long-term effects of percutaneous laser balloon ablation from the canine coronary sinus

BACKGROUND

Radiofrequency catheter ablation of left-sided accessory pathways is becoming the first line of therapy for patients with symptomatic Wolff-Parkinson-White syndrome. Nevertheless, alternative ablation techniques merit development, at least as supplementary modalities for cases in which conventional ablation approaches may prove unsuccessful. We recently reported the short-term results with transcatheter laser balloon ablation from the coronary sinus in a canine model, proving that the procedure is feasible for the potential ablation of left-sided accessory pathways. We now report the effects of percutaneous transcatheter laser balloon ablation in a chronic canine model.

METHODS AND RESULTS

Twenty adult mongrel dogs were studied. After baseline coronary arteriography, left ventriculography, and coronary sinus angiography were obtained, 15 dogs received two or three consecutive laser doses from the coronary sinus of 30-40 W for 15-30 seconds, for a total cumulative energy of 1,200-2,400 J. The five remaining animals underwent a procedure consisting of balloon sham inflation without laser exposure and served as controls. After a mean follow-up of 6 weeks, the angiographic procedures were repeated, and the animals were killed. The mean extent of the fibrotic lesion was 15 mm long, 6 mm wide, and 4.5 mm deep and involved the coronary sinus wall, atrium, and, frequently, the summit of the posterior left ventricular wall. Six animals (four in the study group and two in the control group) showed asymptomatic narrowing of the coronary sinus lumen but always with total angiographic reconstitution due to extensive collateral circulation. The circumflex artery and mitral valve were intact angiographically and histologically in all animals.

CONCLUSIONS

Percutaneous transcatheter laser balloon ablation via the coronary sinus produces a lesion that may be anatomically well suited for left-sided accessory pathway ablation. Although coronary sinus narrowing may occur, adverse physiological effects are unlikely due to the development of extensive collateral circulation. Systematic clinical studies of this new approach to catheter ablation appear warranted.

Age-related change of free radical generation in liver and sex glands of rats

Many investigations have been made on age-related changes of lipid peroxidation in tissue homogenates and subcellular fractions. However, to date there are few reports on the age-related change of free radicals in living organs during aging. In our study, we investigated free radical concentration in liver and sex glands of different aged rats by using electron spin resonance (ESR) technique. A significant reduction of free radicals in liver and sex glands of old aged rats was observed when compared with those of young or middle-aged ones. The decrease of free radical generation during aging is discussed.

[Age-dependent changes of some body functions in male Wistar rats]

It was shown in this experiment that many systematic functions in male Wistar rats gradually declined during aging. Compared with young rats, thymus weight or the weight index decreased significantly in the 13- and 24-month rats (P less than 0.001). Age-dependent decreases of proliferation rate of splenic T lymphocyte, plasma testosterone (T) and estradiol (E2) level, concentration of cytochrome P-450 and activity of mixed functional oxidase (MFO) in liver microsomes were also observed.

Two pathways for iron uptake by guinea pig reticulocytes

We have demonstrated that the intracellular processing of transferrin to effect iron removal involves two pathways, one sensitive to rotenone and the other not. We have also found that the effect of the rotenone is dependent on the transferrin concentration: iron uptake was suppressed with concentrations of transferrin in the micromolar range, and was not suppressed at physiologic concentrations of transferrin. Rotenone does not disturb transferrin's interaction with its extracellular receptor, indicating that its action must be intracellular. The following model is suggested: that separate pathways are entered by transferrin in the cell. The first pathway is preferentially utilized when transferrin is in short supply. It begins with an intracellular site which has a high affinity (and low capacity) for either iron or transferrin. The second pathway begins with an intracellular site which has a high capacity (but low affinity) for either iron or transferrin and is utilized when transferrin is in physiologic concentration (and the low-capacity, high-affinity site is saturated); the pathway it initiates is dominant when transferrin is abundant. We speculate that the high-affinity low-capacity pathway may serve to direct intracellular iron to sites which would be critically injured by iron excess.

Iron bound to low MW ligands: interactions with mitochondria and cytosolic proteins

The iron in the low MW pool of the cell is the precursor of iron in haem and is bound primarily to ATP. This precursor-product relationship suggested that reticulocytes might accumulate ATP-iron if their haem synthesis were blocked. However reticulocytes, treated with succinylacetone or rotenone and taking up iron from transferrin, accumulated iron in nonhaem cytosolic proteins and in mitochondria and not in the low MW pool. This was demonstrated by NMR and also by disrupting the cell with shear stress, separating the cytosol and pellet and fractionating the cytosol with ammonium sulfate. This constancy of the low MW iron pool in the face of blocked haem synthesis could not be explained by saturation of cytosolic ATP or by sluggish exchange of the low MW pool with other compartments. Rather, nonhaem cytosolic proteins and mitochondria appeared to have a higher affinity for iron and to exchange it rapidly with that in the low MW pool.

Mitochondria have Fe(III) receptors

Recent work has provided new evidence that ATP is the major constituent of the low-Mr iron pool in the reticulocyte. The interaction of the iron complex of ATP with mitochondria was investigated in the present experiments. When ATP-Fe3+ was incubated with mitochondria, Fe3+, free of ATP, bound with high affinity to Fe3+ receptors on the mitochondria. The binding was saturable and reversible. Iron which was complexed to PPi, nitrilotriacetate, citrate, ADP and GTP also showed saturable binding to mitochondria; Fe3+ complexed to AMP bound non-specifically, as did Fe2+/ascorbate complexed to AMP bound non-specifically, as did Fe2+/ascorbate and Fe2+/dithionite.

Low molecular weight iron from guinea pig reticulocytes isolated by Sephadex G-25 chromatography

As part of a continuing study of the low MW iron pool, guinea pig reticulocytes were incubated with 59Fe-labeled transferrin, and the reticulocyte hemolysate was chromatographed on Sephadex G-25. 59Fe, in amounts corresponding to that which was in a low MW peak eluting from an Ultrogel column and to that not precipitated by ammonium sulfate, adsorbed to the Sephadex column. The adsorbing 59Fe, on elution from the Sephadex with dilute formic acid, coeluted with phosphate and pentose. When EDTA was added to disrupt the putative iron complex, neither iron nor P adsorbed to the column, supporting the argument that they exist as a compound in the cytosol and adsorb and elute together for that reason. These observations provide additional evidence that P-containing compounds, probably originating as nucleotides, are important components of the low MW iron pool of cells.

Hemolysates reduce iron released from transferrin

Transferrin donates iron to reticulocytes as follows: it binds to a receptor on the reticulocyte surface; the complex is endocytosed; both irons are released and the transferrin is recycled to the cell exterior. It has been proposed that the trigger for iron release after transferrin endocytosis is acidification of the endocytic vesicle. But this could account for removal of only one of transferrin's two irons, since only one of the irons is labile at acid pH. Moreover, iron continues to be removed from transferrin when acidification of the vesicle is blocked by a chloride-transport inhibitor. Thus a detailed explanation of iron removal from transferrin remains elusive. In earlier work we showed that iron can be removed from transferrin by whole hemolysates and also by the combined action of hemoglobin and ATP at pH 7. We now show that the iron released from transferrin by hemolysates, and by hemoglobin and ATP, is in the Fe(II) oxidation state. We also show that ADP and DPG can substitute for ATP and that NADH and NADPH can substitute for the hemoglobin, although with these substitutions Fe(II) is generated less efficiently. The reductive release of iron from transferrin is rapid enough to account for all the iron processed by a young reticulocyte. We speculate that transferrin iron may be reduced to Fe(II) before reaching the mitochondria.