Prospective evaluation of the safety of compounded bulk material L-asparaginase in dogs with lymphoma

Use of compounded L-asparaginase became routine in veterinary oncology when manufacturing of Elspar^® was discontinued in 2012. The objective of this study was to evaluate the safety of compounded L-asparaginase (CLASP, KRS Global Biotechnology, Boca Raton, FL, USA) in comparison with Elspar^® (Lundbeck LLC, Deerfield, IL, USA). In addition, we documented the response to CLASP in combination with a corticosteroid in this population of dogs with lymphoma. Dogs were prospectively treated with 10 000 IU/m² CLASP or Elspar^® subcutaneously. Corticosteroids were administered concurrently. Adverse events (AE) were assessed according to the Veterinary Cooperative Oncology Group Common Terminology Criteria for Adverse Events v1.1 (VCOG-CTCAE). Response was recorded. Seventy-three dogs received 75 treatments (CLASP, n = 47; Elspar^® , n = 28). No AE were attributed to CLASP. Grade I and II AE probably or possibly related to treatment were observed following two Elspar^® treatments. The overall response rate to the combination of CLASP and a corticosteroid was 80% (24% CR and 56% PR). In combination with a steroid, the compounded L-asparaginase evaluated in this study is safe and demonstrates activity against canine lymphoma. In the face of the discontinuation of Elspar^® , veterinarians should seek compounded LASP products that have been tested for activity, purity, and sterility.

Febrile neutropenia in cats treated with chemotherapy

The purpose of this study was to describe the clinical presentation, potential causative agents, treatment and outcome of febrile neutropenia (FN) in chemotherapy-treated cats. Medical records from eight institutions were retrospectively reviewed. A total of 22 FN events in 20 cats were evaluated. Lymphoma was the most common cancer diagnosis; lomustine and vinca alkaloids were the most frequently implicated causative agents. Presenting clinical signs included decreased appetite, lethargy, vomiting and diarrhoea. Median body temperature and absolute neutrophil count at presentation were 104.1 °F; 40 °C (range: 103.1-105.1 °F; 39.5-40.6 °C) and 246 mL^-1 (range: 0-1600 mL^-1 ), respectively. Median number of days between chemotherapy administration and FN onset was 5 (range: 4-25 days). All but one cat were treated with intravenous fluids and broad spectrum antibiotics. Fevers resolved in all cases and absolute neutrophil counts returned to normal in 19 cats. Clinical presentation of cats with FN appears similar to that of dogs.

Treatment time, ease of use and cost associated with use of Equashield™, PhaSeal® , or no closed system transfer device for administration of cancer chemotherapy to a dog model

This prospective experimental simulation study evaluated the efficiency, ease of use (EOU) and cost of administering chemotherapy with two closed system transfer devices (CSTD, Equashield™ and PhaSeal^® ) and no CSTD. Forty-six veterinary technicians (VT) working in oncology specialty practices were timed during chemotherapy administration simulated with water and a model canine limb 10 times with each system and with no CSTD. EOU and likelihood of recommending each system were rated by VT using visual analog scales. Costs were obtained from veterinary distributors. Administration was fastest with Equashield™ (P = 0.0003), but the difference was not enough to affect case flow. Equashield™ was easier to use than PhaSeal^® or no CSTD (P = 0.002), however VT recommended both CSTD more strongly than no CSTD (P < 0.0001). Equashield™ cost less than PhaSeal^® but was sold only in bulk quantities. CSTD did not decrease efficiency in administering chemotherapy and were readily accepted by VT.

Recurrent reciprocal deletions and duplications of 16p13.11: the deletion is a risk factor for MR/MCA while the duplication may be a rare benign variant

BACKGROUND

Genomic disorders are often caused by non-allelic homologous recombination between segmental duplications. Chromosome 16 is especially rich in a chromosome-specific low copy repeat, termed LCR16.

METHODS AND RESULTS

A bacterial artificial chromosome (BAC) array comparative genome hybridisation (CGH) screen of 1027 patients with mental retardation and/or multiple congenital anomalies (MR/MCA) was performed. The BAC array CGH screen identified five patients with deletions and five with apparently reciprocal duplications of 16p13 covering 1.65 Mb, including 15 RefSeq genes. In addition, three atypical rearrangements overlapping or flanking this region were found. Fine mapping by high-resolution oligonucleotide arrays suggests that these deletions and duplications result from non-allelic homologous recombination (NAHR) between distinct LCR16 subunits with >99% sequence identity. Deletions and duplications were either de novo or inherited from unaffected parents. To determine whether these imbalances are associated with the MR/MCA phenotype or whether they might be benign variants, a population of 2014 normal controls was screened. The absence of deletions in the control population showed that 16p13.11 deletions are significantly associated with MR/MCA (p = 0.0048). Despite phenotypic variability, common features were identified: three patients with deletions presented with MR, microcephaly and epilepsy (two of these had also short stature), and two other deletion carriers ascertained prenatally presented with cleft lip and midline defects. In contrast to its previous association with autism, the duplication seems to be a common variant in the population (5/1682, 0.29%).

CONCLUSION

These findings indicate that deletions inherited from clinically normal parents are likely to be causal for the patients' phenotype whereas the role of duplications (de novo or inherited) in the phenotype remains uncertain. This difference in knowledge regarding the clinical relevance of the deletion and the duplication causes a paradigm shift in (cyto)genetic counselling.

Idiopathic learning disability and genome imbalance

Learning disability (LD) is a very common, lifelong and disabling condition, affecting about 3% of the population. Despite this, it is only over the past 10-15 years that major progress has been made towards understanding the origins of LD. In particular, genetics driven advances in technology have led to the unequivocal demonstration of the importance of genome imbalance in the aetiology of idiopathic LD (ILD). In this review we provide an overview of these advances, discussing technologies such as multi-telomere FISH and array CGH that have already emerged as well as new approaches that show diagnostic potential for the future. The advances to date have highlighted new considerations such as copy number polymorphisms (CNPs) that can complicate the interpretation of genome imbalance and its relevance to ILD. More importantly though, they have provided a remarkable approximately 15-20% improvement in diagnostic capability as well as facilitating genotype/phenotype correlations and providing new avenues for the identification and understanding of genes involved in neurocognitive function.

Screening for subtelomeric chromosome abnormalities in children with idiopathic mental retardation using multiprobe telomeric FISH and the new MAPH telomeric assay

Subtelomeric chromosomal abnormalities are emerging as an important cause of human genetic disorders. The scope of this investigation was to screen a selected group of children with idiopathic mental retardation for subtelomeric anomalies using the multiprobe telomeric FISH method and also to develop and test a new assay, the MAPH telomeric assay, in the same group of patients. The new MAPH telomeric assay uses the recently published MAPH methodology that permits the measurement of locus copy number by hybridisation with a specifically designed set of probes located at the end of human chromosomes. Seventy patients with idiopathic mental retardation have been screened using the established multiprobe telomeric FISH assay and the new MAPH telomeric assay, for all telomeres. One patient with de novo 8p subtelomeric deletion was identified. The new MAPH telomeric assay confirmed the same results in both normal and abnormal samples. This is the first description of the use of MAPH methodology to detect chromosomal imbalances near the telomeres in idiopathic mentally retarded patients. The new MAPH telomeric assay offers a new, fast, accurate and cost effective diagnostic tool to detect chromosomal imbalances near telomeres in mentally retarded patients, as well as the characterisation of known chromosomal abnormalities, spontaneous recurrent miscarriages, infertility, hematological malignancies, preimplantation genetic diagnosis, and other fields of clinical and research interests.

Submicroscopic 8pter deletion, mild mental retardation, and behavioral problems caused by a familial t(8;20)(p23;p13)

Microscopically visible distal 8p deletions have been associated with growth and mental impairment, minor facial anomalies, congenital heart defects, and behavioral problems. We report two cousins with mild retardation and behavioral problems, including inappropriate sexual behavior and pyromania. Familial learning difficulties on the grandfather's side incompatible with Mendelian inheritance prompted telomere screening, which detected a submicroscopic terminal 8p deletion of < 5.1 Mb. The cousins' mothers both carried a t(8;20)(p23;p13) balanced translocation. The frequently observed microcephaly in patients with microscopically visible deletions of 8pter is lacking in both cousins, suggesting that the gene(s) causing the microcephaly is centromeric to the deleted region. The absence of cardiac defects in the cousins confirms the more proximal location of gene(s) causing these abnormalities in other reported cases with microscopically visible 8pter deletions and supports involvement of the GATA4 gene. Moreover, the current cases predict the presence of a putative gene(s) involved in behavior in the most telomeric 5.1 Mb of the p-arm of chromosome 8. This first clinical report of a submicroscopic subtelomeric 8p deletion gives more insight into the so-called 8p- syndrome and demonstrates the difficulty in making a clinical diagnosis for a submicroscopic 8pter deletion in an individual patient with mental retardation.

Clinical studies on submicroscopic subtelomeric rearrangements: a checklist

BACKGROUND

Submicroscopic subtelomeric chromosome defects have been found in 7.4% of children with moderate to severe mental retardation and in 0.5% of children with mild retardation. Effective clinical preselection is essential because of the technical complexities and cost of screening for subtelomere deletions.

METHODS

We studied 29 patients with a known subtelomeric defect and assessed clinical variables concerning birth history, facial dysmorphism, congenital malformations, and family history. Controls were 110 children with mental retardation of unknown aetiology with normal G banded karyotype and no detectable submicroscopic subtelomeric abnormalities.

RESULTS

Prenatal onset of growth retardation was found in 37% compared to 9% of the controls (p<0.0005). A higher percentage of positive family history for mental retardation was reported in the study group than the controls (50% v 21%, p=0.002). Miscarriage(s) were observed in only 8% of the mothers of subtelomeric cases compared to 30% of controls (p=0.028) which was, however, not significant after a Bonferroni correction. Common features (>30%) among subtelomeric deletion cases were microcephaly, short stature, hypertelorism, nasal and ear anomalies, hand anomalies, and cryptorchidism. Two or more facial dysmorphic features were observed in 83% of the subtelomere patients. None of these features was significantly different from the controls. Using the results, a five item checklist was developed which allowed exclusion from further testing in 20% of the mentally retarded children (95% CI 13-28%) in our study without missing any subtelomere cases. As our control group was selected for the "chromosomal phenotype", the specificity of the checklist is likely to be higher in an unselected group of mentally retarded subjects.

CONCLUSIONS

Our results suggest that good indicators for subtelomeric defects are prenatal onset of growth retardation and a positive family history for mental retardation. These clinical criteria, in addition to features suggestive of a chromosomal phenotype, resulted in the development of a five item checklist which will improve the diagnostic pick up rate of subtelomeric defects among mentally retarded subjects.

Neurodevelopmental profile of a new dysmorphic syndrome associated with submicroscopic partial deletion of 1p36.3

We describe four children with dysmorphic syndrome with severe learning disability (SLD). Their chromosomes had been normal on conventional cytogenetic examination. However, screening using a multiprobe fluorescence in situ hybridisation (FISH) technique for subtelomeric abnormalities revealed a deletion of the p arm of chromosome 1. The physical features include body asymmetry, microcephaly, distinctive facies with deep-set eyes, sharply defined eye sockets, and mid-face hypoplasia; the neurodevelopmental profile was characterised by SLD, motor delay with hypotonia, markedly delayed visual maturation, and postural asymmetry together with epilepsy. This phenotype is consistent with that described for partial monosomy for 1p36.3.

Subtle chromosomal rearrangements in children with unexplained mental retardation

BACKGROUND

No explanation for moderate to severe mental retardation is apparent in about 40% of cases. Although small chromosomal rearrangements may account for some undiagnosed cases, a lack of genome-wide screening methods has made it impossible to ascertain the frequency of such abnormalities.

METHODS

A fluorescence in-situ hybridisation (FISH) test was used to examine the integrity of chromosome ends in 284 children with unexplained moderate to severe retardation, and in 182 children with unexplained mild retardation. 75 normal men were also tested. When a chromosomal rearrangement was found, its size was estimated, and members of the child's family were investigated.

FINDINGS

Subtle chromosomal abnormalities occurred with a frequency of 7.4% in the children with moderate to severe mental retardation, and of 0.5% in the children with mild retardation. The abnormalities had an estimated population prevalence of 2.1 per 10,000, and were familial in almost half of cases.

INTERPRETATION

Once recognisable syndromes have been excluded, abnormalities that include the ends of chromosomes are the commonest cause of mental retardation in children with undiagnosed moderate to severe mental retardation. Owing to the high prevalence of familial cases, screening for subtle chromosomal rearrangements is warranted in children with unexplained moderate to severe mental retardation.

cDNA cloning of a human dishevelled DVL-3 gene, mapping to 3q27, and expression in human breast and colon carcinomas

dishevelled (Dsh) is a member of the segment polarity gene family in Drosophila which plays an important role in the early developmental patterning processes. A human homologue of Dsh (DVL-1) has recently been described. Here, we report the cloning of a second human homologue of Dsh (called DVL-3) by cDNA library screening. The human DVL-3 gene encodes a predicted 716 amino acid protein which exhibits 98% amino acid identity with mouse Dvl-3 and 49% with Drosophila Dsh. DVL-3 was mapped to 3q27. The expression of DVL-3 mRNA was detected in 30 human cell lines and 2 primary cell cultures. DVL-3 mRNA was detected in normal human breast tissues (n = 4) and tumours (n = 25). Statistically, there was no difference in DVL-3 mRNA level between normal breast tissues and tumours. In human colorectal samples, DVL-3 was expressed equally in matched normal tissues, polyps and tumours. The data indicates that DVL-3 is widely expressed in human cells and supports the notion of a new developmental gene family for dishevelled which may have a widespread role in signal transduction.

The unique heme-heme interactions of the homodimeric Scapharca inaequivalvis hemoglobin as probed in the protein reconstituted with unnatural 2,4 heme derivatives

In the homodimeric hemoglobin from Scapharca, HbI, functional communication between the two heme groups is based on their direct structural linkage across the subunit interface through the heme propionates. The heme-protein interactions have been altered in deutero- and meso-HbI by substituting the vinyl groups at positions 2 and 4 of protoheme with hydrogen and ethyl groups, respectively. In meso-HbI the introduction of the ethyl groups in the heme pocket induces significant alterations in the conformation of the heme peripheral substituents, including the propionates, and in the structure of bound CO, as revealed by the resonance Raman spectra. The functional counterpart of these structural changes is the loss of cooperativity in carbon monoxide binding and in the rate of oxygen dissociation. Oxygen pulse and flash photolysis experiments indicate that meso-HbI is locked in the liganded conformation. It is postulated that the ethyl groups, which occupy a larger volume than vinyl ones, impair the ligand-linked movement of the heme relative to its pocket and in turn the expression of cooperativity. In deutero-HbI structural alterations have not been monitored. Functionally, cooperativity in the CO binding kinetics is increased as if hydrogen atoms at positions 2 and 4 permitted more marked movements of the heme than in the native protein.

Development and clinical application of an innovative fluorescence in situ hybridization technique which detects submicroscopic rearrangements involving telomeres

We report an innovative fluorescence in situ hybridization technique which exploits a unique resource of 41 telomere-specific probes and allows the simultaneous analysis of the subtelomeric region of every chromosome for deletion, triplication and balanced translocation events. This technique requires only a single microscope slide per patient and is expected to be a useful diagnostic tool with applications in the fields of idiopathic mental retardation, the detection of congenital abnormalities and in some forms of cancer. This will lead to more accurate genetic counselling of patients and their families and will provide the basis for future diagnostic, therapeutic and preventative measures.

Structural and functional effects of apolar mutations of the distal valine in myoglobin

High-resolution structures of the aquomet, deoxy, and CO forms of Ala68, Ile68, Leu68, and Phe68 sperm whale myoglobins have been determined by X-ray crystallography. These 12 new structures, plus those of wild-type myoglobin, have been used to interpret the effects of mutations at position 68 and the effects of cobalt substitution on the kinetics of O2, CO, and NO binding. Molecular dynamics simulations based on crystal structures have provided information about the time-dependent behavior of photolyzed ligands for comparison with picosecond geminate recombination studies. The Val68-->Ala mutation has little effect on the structure and function of myoglobin. In Ala68 deoxymyoglobin, as in the wild-type protein, a water molecule hydrogen-bonded to the N epsilon atom of the distal histidine restricts ligand binding and appears to be more important in regulating the function of myoglobin than direct steric interactions between the ligand and the C gamma atoms of the native valine side-chain. This distal pocket water molecule is displaced by the larger side-chains at position 68 in the crystal structures of Leu68 and Ile68 deoxymyoglobins. The Leu68 side-chain can rotate about its C alpha-C beta and C beta-C gamma bonds to better accommodate bound ligands, resulting in net increases in overall association rate constants and affinities due to the absence of the distal pocket water molecule. However, the flexibility of Leu68 makes simulation of picosecond NO recombination difficult since multiple starting conformations are possible. In the case of Ile68, rotation of the substituted side-chain is restricted due to branching at the beta carbon, and as a result, the delta methyl group is located close to the iron atom in both the deoxy and liganded structures. The favorable effect of displacing the distal pocket water molecule is offset by direct steric hindrance between the bound ligand and the terminal carbon atom of the isoleucine side-chain, resulting in net decreases in affinity for all three ligands and inhibition of geminate recombination which is reproduced in the molecular dynamics simulations. In Phe68 myoglobin, the benzyl side-chain is pointed away from the ligand binding site, occupying a region in the back of the distal pocket. As in wild-type and Ala68 myoglobins, a well-defined water molecule is found hydrogen bonded to the distal histidine in Phe68 deoxymyoglobin. This water molecule, in combination with the large size of the benzyl side-chain, markedly reduces the speed and extent of ligand movement into the distal pocket. (ABSTRACT TRUNCATED AT 400 WORDS)

Nitric oxide recombination to double mutants of myoglobin: role of ligand diffusion in a fluctuating heme pocket

Picosecond recombination of nitric oxide to the double mutants of myoglobin, His64Gly-Val68Ala and His64Gly.Val68Ile, at E7 and E11, has been studied experimentally and by computation. It is shown that distal residues have a profound effect on NO recombination. Recombination in the mutants may be explained in terms of fluctuating free volume and structure of the heme pocket. The double mutants provide insight into the effects of free volume and steric hindrance on rates of ligand rebinding following photolysis. Water molecules of the first solvation shell replace surface residues deleted by mutation and can block apparent holes in the protein structure. Thus, water molecules extend the time required for ligands to escape significantly to a nanosecond time scale, which is much longer than would be expected for an open heme pocket. Both nearly exponential (G64A68) and markedly nonexponential (native and G64I68) kinetics are observed, a result at variance with expectation from the model of Petrich et al. [Petrich, J.W., Lambry, J.C., Kuczera, K., Karplus, M., Poyart, C., & Martin, J.L. (1991) Biochemistry 30, 3975-3987], which attributes nonexponential kinetics to proximal effects.

Kinetics of ligand binding to Pseudoterranova decipiens and Ascaris suum hemoglobins and to Leu-29-->Tyr sperm whale myoglobin mutant

The kinetics of binding of O2, CO, and NO to the octameric, two-domain hemoglobins of the parasitic nematodes Pseudoterranova decipiens and Ascaris suum were determined on nanosecond and picosecond time scales using flash photolysis. The two nematode hemoglobins have very similar kinetic properties. On the picosecond time scale, they exhibit an unusual behavior in showing a geminate reaction with oxygen that is biphasic and dependent on the flash intensity. The geminate reaction with NO is also faster and more complete than for sperm whale myoglobin; however, in contrast to the O2 reaction, it is homogeneous. In addition, the oxygen dissociation rate of P. decipiens hemoglobin, 0.0035 s-1, is as low as that of A. suum hemoglobin, 0.004 s-1 (Gibson, Q. H., and Smith, M. H. (1965) Proc. R. Soc. Lond. B Biol. Sci. 163, 206-214). A mutant of sperm whale myoglobin suggested by sequence alignment of the nematode hemoglobins, Leu-29-->Tyr, did not have kinetic properties similar to them.

Ligand binding and slow structural changes in chlorocruorin from Spirographis spallanzanii

Chlorocruorin is a cooperative respiratory pigment found in the blood of polychaete worms; its prosthetic group is a derivative of the iron protoporphyrin IX, in which the vinyl group at position 2 is substituted by a formyl group. The quaternary structure of chlorocruorins is complex: myoglobin-like subunits are grouped in tetramers and tetramers in dodecamers; 12 dodecamers are assembled in the 3500-kDa particle. Chlorocruorin from Spirographis spallanzanii displays the following overall functional properties: (i) the oxygen affinity is lower than in human hemoglobin, while that of CO is similar if not higher; (ii) the rates of combination with oxygen and carbon monoxide are low; and (iii) the off rate of oxygen is comparable to that of human hemoglobin, while the off rate of CO is 10 times smaller. When CO is partially photolyzed with a long and powerful light flash (70 microseconds), rebinding is biphasic as in mammalian hemoglobins; however, the slowest rate is faster than that observed by stopped flow, suggesting that the unliganded protein decays from the liganded high affinity state (R) to an intermediate state before reaching the low affinity (T) state. Oxygen binding was followed by stopped-flow and flash photolysis. While partial photolysis yields a fast, second-order time course, stopped-flow experiments yield slow, biphasic, and non-second-order time courses. This pattern of reactivity was attributed to a slow conformational transition(s) which is (are) rare limiting with oxygen, but not with CO.(ABSTRACT TRUNCATED AT 250 WORDS)

Ligand diffusion in the distal heme pocket of myoglobin. A primary determinant of geminate rebinding

There are at least two picosecond kinetic components in the rebinding of NO to native sperm whale myoglobin. Petrich et al. (Petrich, J. W., Lambry, J.-C., Kuczera, K., Karplus, M., Poyart, C., and Martin, J.-L. (1991) Biochemistry 30, 3975-3987) attribute the slowing of the reaction to a movement of the iron atom out of the plane of the heme following ligand dissociation. In contrast, Gibson et al. (Gibson, Q. H., Regan, R., Elber, R., Olson, J. S., and Carver, T. E. (1992) J. Biol. Chem. 267, 22022-22034) have explained multiphasic geminate reactions by diffusion of NO into the distal heme pocket as determined by its detailed structure. O2 and NO rebinding to iron and cobalt derivatives of native, V68F, and V68I sperm whale myoglobin has been examined. Each iron protein shows a biphasic time course of NO rebinding reactions with widely different rates and amplitudes. Although cobalt does not move out of the plane of the porphyrin on ligand removal, the reactions of the iron and cobalt derivatives of each protein were closely similar. The time course of O2 rebinding to cobalt was also similar to that of NO rebinding to iron. These results are consistent with a primary role for the structure of the distal pocket in determining diffusion of ligands away from the metal atom and as a result the time course of picosecond ligand rebinding.

Ligand binding and conformation change in the dimeric hemoglobin of the clam Scapharca inaequivalvis

The reaction with carbon monoxide of the cooperative dimeric hemoglobin from Scapharca inaequivalvis has been examined by flash photolysis. In the nanosecond time range, geminate rebinding of 5% of dissociated CO occurs with a rate constant of 1.4 x 10(7) s-1. There is a change in absorbance of deoxyhemoglobin following photolysis at a rate of 1.2 x 10(6) s-1, consistent with a shift in the position of the Soret band to longer wavelengths. The amplitude of the change is proportional to the population of deoxydimer. In much of the Soret region this change is greater than the absorbance excursion associated with geminate recombination. There is at least one other slower change associated with the singly liganded species. Geminate rebinding of NO has components of 50, 8, and 0.035 ns-1, accounting for 75%, 25%, and less than 1% of the total reaction observed after a 35-ps photolysis flash. Simulation of diffusion of NO by molecular dynamics shows the ligands moving from the heme pocket to a subsidiary space between the edge of the heme and the surface of the protein.

Distal pocket residues affect picosecond ligand recombination in myoglobin. An experimental and molecular dynamics study of position 29 mutants

Time courses for intramolecular NO and O2 recombination to native and three position 29 mutants of sperm whale myoglobins were measured after laser photolysis on picosecond and nanosecond time scales. The rates for the first phase of NO recombination were 1.8, 2.5, 29, and > or = 100 ns-1 for Ala29, Val29, Leu29 (native), and Phe29 myoglobin, respectively, at room temperature. This order is not correlated with the overall association rate constants for NO binding which were all in the range 20-50 x 10(6) M-1 s-1 and is the opposite of that observed for the rate constants for the overall thermal dissociation of NO which were 5.0, 2.8, 0.98, and 0.21 x 10(-4) s-1 for Ala29, Val29, Leu29 (native), and Phe29 myoglobin, respectively, at 20 degrees C. This inverse correlation suggests that photo- and thermally dissociated ligand molecules experience similar kinetic and equilibrium barriers to rebinding. The larger side chains of Leu29 and Phe29 inhibit rapid movement of the ligand away from the iron atom facilitating geminate recombination. The smaller side chains of Val29 and Ala29 increase the space available to the ligand, decreasing the rate of geminate recombination and enhancing complete dissociation. Diffusion of NO in the distal pocket of myoglobin was simulated using a variant of the molecular dynamics program CHARMM that includes the locally enhanced sampling protocol (Elber, R., and Karplus, M. (1991) J. Am. Chem. Soc. 112, 9161-9175; Roitberg, A., and Elber, R. (1991) J. Chem. Phys. 95, 9277-9287) and the x-ray structures of Carver et al. (Carver, T. E., Brantley, R. E., Jr., Singleton, E. W., Arduini, R. M., Quillin, M. L., Phillips, G. N., Jr., and Olson, J. S. (1992) J. Biol. Chem. 267, 14443-14450). Both accelerated (5,000 K) and room temperature ligands were used, and comparisons were made between simulations with a complete hydration shell surrounding the protein and those with only eight water molecules near the distal histidine. Photodissociated ligands initially move away from the heme plane, past Leu29, and toward Leu32, Phe33, Ile107, and Ile111. These theoretical results confirm that a complete description of picosecond ligand recombination must include the dynamics of ligand movement in the distal portion of the heme pocket.

Ligand binding by the chlorocruorin from Eudistylia vancouverii

Carbon monoxide chlorocruorin from Eudistylia vancouverii shows three distinct first-order relaxations with rates of 2.9 x 10(9) s-1, 6.5 x 10(7) s-1, and 3.2 x 10(6) s-1 (geminate reactions) and three second-order relaxations with rates of 4.7 x 10(6) M-1 s-1, 7 x 10(5) M-1 s-1, and 7 x 10(4) M-1 s-1, when studied by flash photolysis. The amplitudes of the second-order reactions depend on the extent of photolysis. This may be due to relaxation from the liganded (R) to the unliganded (T) conformation following photolysis and suggests that the combination rates contribute to cooperativity. In a stopped-flow experiment only the slowest phase with a rate of 7 x 10(4) M-1 s-1 is observed. It is assigned to binding to the T-state protein. Fragments of the native protein containing 12 and 4 hemes react like the holoprotein suggesting that the tetramer is a major cooperative unit. Oxygen binding shows three geminate relaxations with rates of 2.5 x 10(10) s-1, 3.5 x 10(7) s-1, and 4.5 x 10(6) s-1, and two second-order rates of 1.5 x 10(7) M-1 s-1 and 1 x 10(6) M-1 s-1. The amplitudes of the second-order phases do not correlate with the extent of photolysis. The results with the two ligands are consistent with an allosteric transition fast enough to compete with a rebinding rate of 500 s-1 in the R to T direction (CO rebinding) but not fast enough to compete with oxygen rebinding. There is significant heterogeneity in the R-state kinetics, but the T-state reaction is homogeneous.

Ligand binding in a hierarchy of globin complexes. The hexagonal bilayer hemoglobin of Lumbricus terrestris and its heme-containing subunits

The kinetics of CO and NO recombination with the giant approximately 3600-kDa hexagonal bilayer hemoglobin of Lumbricus terrestris and its subunits, the approximately 200-kDa dodecamer of globin chains (3 x chains (I + II + III + IV] (see preceding paper (Vinogradov S.N., Sharma, P.K., Qabor, A.N., Wall, J.S., Westrick, J.A., Simmons, J.H., and Gill, S.J. (1991) J. Biol. Chem. 266, 13091-13096], the 50-kDa disulfide-bonded trimer (chains II-IV), the monomer (chain I), and the approximately 30-kDa linker (chains VA, VB, and VI), were measured following photolysis over time scales ranging from picosecond to millisecond. CO recombination at 436 nm subsequent to excitation (9 ns) at 532 nm showed three phases covering a 100-fold range for the Hb, dodecamer, trimer, and linker protein. The proportion of the fast phase was 0.1-0.2 for the trimer, dodecamer, and Hb. The relative rates and amplitudes of the phases were not affected by changes in CO concentration or excitation intensity. The monomer showed a single phase with a rate of 2 x 10(6) M-1 s-1. The second-order reaction with NO showed two rates. The faster rate was 90 x 10(6) M-1 s-1 and accounted for approximately 0.7 of the reaction for all species except the monomer, where it accounted for the full reaction. The slower rate was 15 x 10(6) M-1 s-1 for all species except the monomer.

Validation of an automated determination of pulmonary resistance by electrical subtraction

An analog computer to determine dynamic pulmonary compliance (C) and pulmonary resistance (R) on a breath-by-breath basis was tested in guinea pigs and dogs. C was determined by dividing volume by transpulmonary pressure at instants of zero flow. R was determined by the method of electrical subtraction at predetermined flows. In both species the computer outputs and the results of direct analysis were in close agreement. In guinea pigs, the device reliably followed the rapid three- to fourfold changes in C and R resulting from histamine infusion. In unanesthetized dogs, the dispersion and mean values of C and R were similar by the two methods.