Chimeric human antibody molecules: mouse antigen-binding domains with human constant region domains

We have created mouse-human antibody molecules of defined antigen-binding specificity by taking the variable region genes of a mouse antibody-producing myeloma cell line with known antigen-binding specificity and joining them to human immunoglobulin constant region genes using recombinant DNA techniques. Chimeric genes were constructed that utilized the rearranged and expressed antigen-binding variable region exons from the myeloma cell line S107, which produces an IgA (kappa) anti-phosphocholine antibody. The heavy chain variable region exon was joined to human IgG1 or IgG2 heavy chain constant region genes, and the light chain variable region exon from the same myeloma was joined to the human kappa light chain gene. These genes were transfected into mouse myeloma cell lines, generating transformed cells that produce chimeric mouse-human IgG (kappa) or IgG (kappa) anti-phosphocholine antibodies. The transformed cell lines remained tumorigenic in mice and the chimeric molecules were present in the ascitic fluids and sera of tumor-bearing mice.

The use of synthetic oligonucleotides as hybridization probes. II. Hybridization of oligonucleotides of mixed sequence to rabbit beta-globin DNA

Two oligonucleotides 14-bases long were synthesized, one complementary to rabbit beta-globin DNA (R beta G14A) and the other with the same sequence except for a single base change (T for C) (R beta G14B). Hybridization conditions were established such that R beta G14A would hybridize to globin DNA while R beta G14B would not. We also synthesized a mixture of 13-base long oligonucleotides (R beta G13Mix), representing eight of the possible coding sequences for amino acids 15-19 of rabbit beta-globin. One of the eight is complementary to globin DNA. R beta G13Mix was found to hybridize specifically to globin DNA under conditions where oligonucleotides forming single base pair mismatches do not. Furthermore, R beta G13Mix was shown to hybridize specifically to colonies containing a plasmid with a globin DNA insert. These results are discussed with respect to a general procedure for screening recombinant clones for those containing DNA coding for a protein of known amino acid sequence.

A set of synthetic oligodeoxyribonucleotide primers for DNA sequencing in the plasmid vector pBR322

Seven oligonucleotide primers complementary to the plasmid vector pBR322 at positions adjacent to five of the unique restriction endonuclease cleavage sites (EcoRI, HindIII, BamHI, SalI and PstI) have been chemically synthesized. The polarity of the primers is such that any DNA inserted at one or a combination of two of the above restriction sites may be sequenced by the chain termination method using one of the synthetic DNA primers. One of the primers for sequencing inserts at the PstI site of pBR322 is also complementary to the M13 phage vector designated bla6. This set of universal primers is useful for rapid sequence determination of DNA cloned into pBR322 or M13bla6.

Towards an expert consensus to delineate a clinical syndrome of chronic breathlessness

Breathlessness that persists despite treatment for the underlying conditions is debilitating. Identifying this discrete entity as a clinical syndrome should raise awareness amongst patients, clinicians, service providers, researchers and research funders.Using the Delphi method, questions and statements were generated via expert group consultations and one-to-one interviews (n=17). These were subsequently circulated in three survey rounds (n=34, n=25, n=31) to an extended international group from various settings (clinical and laboratory; hospital, hospice and community) and working within the basic sciences and clinical specialties. The a priori target agreement for each question was 70%. Findings were discussed at a multinational workshop.The agreed term, chronic breathlessness syndrome, was defined as breathlessness that persists despite optimal treatment of the underlying pathophysiology and that results in disability. A stated duration was not needed for "chronic". Key terms for French and German translation were also discussed and the need for further consensus recognised, especially with regard to cultural and linguistic interpretation.We propose criteria for chronic breathlessness syndrome. Recognition is an important first step to address the therapeutic nihilism that has pervaded this neglected symptom and could empower patients and caregivers, improve clinical care, focus research, and encourage wider uptake of available and emerging evidence-based interventions.

Once-daily opioids for chronic dyspnea: a dose increment and pharmacovigilance study

CONTEXT

Randomized controlled trials can answer questions of efficacy, but long-term pharmacovigilance studies generate complementary safety data.

OBJECTIVES

Level I evidence supports short-term efficacy of opioids in reducing chronic refractory dyspnea. This study aimed to determine the minimum effective once-daily dose of sustained-release morphine, and whether net clinical benefits are sustained safely.

METHODS

In a Phase II dose increment study, 10mg daily of sustained-release morphine was administered, and increased in nonresponders by 10mg daily each week to a maximum of 30 mg daily. The participant was withdrawn if there were unacceptable side effects or no response to maximum dose. If participants had a 10% improvement in dyspnea over their own baseline, they joined a long-term Phase IV effectiveness/safety study at that dose. Complying with Strengthening the Reporting of Observational Studies in Epidemiology (STROBE) guidelines, response and side effects are described, with demographic and clinical characteristics of responders.

RESULTS

Eighty-three participants (53 males, mean age 75 years, 54% with chronic obstructive pulmonary disease) provided more than 30 patient-years of data. Fifty-two participants derived ≥ 10% benefit (on average 35% improvement over baseline), giving a response rate of 62% (number needed to treat of 1.6: number needed to harm 4.6); for 70%, this dose was 10mg/24h. Benefit was maintained at three months for 28 (33%) people. Ranking of breathlessness was reduced significantly (P<0.001), but constipation increased (P<0.001) despite laxatives. There were no episodes of respiratory depression or hospitalizations as a result of the sustained-release morphine. Overall, one in three people continued to derive benefit at three months.

CONCLUSION

Ten milligrams of sustained-release oral morphine once daily is safe and effective for most people who respond.

Medical, psychosocial, and behavioral risk factors do not explain the increased risk for low birth weight among black women

OBJECTIVE

Our purpose was to determine whether various demographic, behavioral, housing, psychosocial, or medical characteristics explain the difference in pregnancy outcome between black and white women.

STUDY DESIGN

A sample of 1491 multiparous women with singleton pregnancies, 69% of whom were black and 31% of whom were white and who enrolled for care between Oct. 1, 1985, and March 30, 1988, participated in the study. The frequencies of various demographic, medical environmental, and psychosocial risk factors among black and white women were determined. The outcome measures were birth weight, gestational age, fetal growth restriction, preterm delivery and low birth weight.

RESULTS

White infants were heavier and born later than black infants. The white women in this sample smoked more cigarettes, moved more frequently, and had worse psychosocial scores. The black women had lower incomes, were less likely to be married, and had more hypertension, anemia, and diabetes. Besides race, only maternal height, weight, blood pressure, diabetes, and smoking had a consistent impact on outcome and did not explain the difference in outcome between the two groups.

CONCLUSION

In this low-income population, many of the risk factors for low birth weight were more common among white women than black women. Nevertheless, black women had more infants born preterm, with growth restriction, and with low birth weight than did white women. The various maternal characteristics studied did not explain these differences.

Molecular cloning and expression of human tumor necrosis factor and comparison with mouse tumor necrosis factor

U-937 cells, a monocytic line derived from a human histiocytic lymphoma, were induced for human tumor necrosis factor (TNF) secretion into the medium and were used for the preparation of TNF mRNA. Biological activity of the latter was quantified in a Xenopus laevis oocyte injection system. TNF mRNA was enriched by gradient centrifugation and this size-fractionated mRNA was used for synthesis of cDNA and inserted into the unique PstI site of pAT153. A recombinant plasmid containing human TNF cDNA was selected by colony hybridization using an internal fragment of a mouse TNF cDNA clone [Fransen, L., Mueller, R., Marmenout, A., Tavernier, J., Van der Heyden, J., Kawashima, E., Chollet, A., Tizard, R., Van Heuverswyn, H., Van Vliet, A., Ruysschaert, M. R. & Fiers, W. (1985) Nucleic Acids Res. 13, 4417-4429] as a probe. The sequence of this human TNF cDNA is in agreement with the one published by Pennica et al. [Pennica, D., Nedwin, G. E., Hayflick, J. S., Seeburg, P. H., Derynck, R., Palladino, M. A., Kohr, W. J., Aggarwal, B. B. & Goeddel, D. V. (1984) Nature (Lond.) 312, 724-729]. The 157-amino-acid-long mature sequence is about 80% homologous to mouse TNF and its hydrophilicity plot is also very similar, in spite of the apparent species specificity of TNF. In contrast to mouse TNF, it contains no potential N-glycosylation site. When compared to other cytokines, like IFN-beta, IFN-gamma, or IL-2, there is a remarkably high preference for G X C pairs in the third-letter positions. Expression of the TNF cDNA in monkey COS cells or in Escherichia coli gives rise to a protein having similar biological and serological properties as natural human TNF. A human genomic clone was also identified and sequenced; it was found to be in good agreement with the one recently published by Shirai et al. [Shirai, T., Yamaguchi, H., Ito, H., Todd, C. W. & Wallace, R. B. (1985) Nature (Lond.) 313, 803-806], except for some differences in the introns and 5'-untranslated region.

Oligonucleotide directed mutagenesis of the human beta-globin gene: a general method for producing specific point mutations in cloned DNA

A nonadecanucleotide has been used both as a site specific mutagen to introduce a T leads to A transversion mutation in the human beta-globin gene cloned in pBR322 as well as a probe to screen transformed colonies for the desired mutant. The specificity of the oligonucleotide as a mutagen and as a hybridization probe provide a general method for producing site specific mutations in DNA cloned in plasmid vectors such as pBR322.

Relationship between markers of malnutrition and clinical outcomes in older adults with cancer: systematic review, narrative synthesis and meta-analysis

Malnutrition predicts poorer clinical outcomes for people with cancer. Older adults with cancer are a complex, growing population at high risk of weight-losing conditions. A number of malnutrition screening tools exist, however the best screening tool for this group is unknown. The aim was to systematically review the published evidence regarding markers and measures of nutritional status in older adults with cancer (age ≥ 70). A systematic search was performed in Ovid Medline, EMBASE, Web of Science, CINAHL, British Nursing Database and Cochrane CENTRAL; search terms related to malnutrition, cancer, older adults. Titles, abstracts and papers were screened and quality-appraised. Data evaluating ability of markers of nutritional status to predict patient outcomes were subjected to meta-analysis or narrative synthesis. Forty-two studies, describing 15 markers were included. Meta-analysis found decreased food intake was associated with mortality (OR 2.15 [2.03-4.20] p = < 0.00001) in univariate analysis. Prognostic Nutritional Index (PNI) was associated with overall survival (HR 1.89 [1.03-3.48] p = 0.04). PNI markers (albumin, total lymphocyte count) could be seen as markers of inflammation rather than nutrition. There a suggested relationship between very low body mass index (BMI) (<18 kg/m2) and clinical outcomes. No tool was identified as appropriate to screen for malnutrition, as distinct from inflammatory causes of weight-loss. Risk of cancer-cachexia and sarcopenia in older adults with cancer limits the tools analysed. Measures of food intake predicted mortality and should be included in clinical enquiry. A screening tool that distinguishes between malnutrition, cachexia and sarcopenia in older adults with cancer is needed.

Radiation of human mitochondria DNA types analyzed by restriction endonuclease cleavage patterns

Human mitochondrial DNA (mtDNA) restriction endonuclease fragment patterns were analyzed using total blood cell DNA isolated from 200 individuals representing five different populations. Thirty-two fragment patterns (morphs) were observed with the enzymes Hpa I, Bam HI, Hae II, Msp I and Ava II yielding thirty-five different combinations of fragment patterns (mt DNA types). The major ethnic groups exhibit quantitative as well as qualitative differences in their mtDNA types, all of which are related to each other by a tree in which the closely related mtDNA types cluster according to geographic origin. Three mtDNA types are postulated to be 'central' to ethnic radiations due to their high frequencies, their appearance in more than one ethnic group, or their presence in other primate species. Genetic distances among populations were computed and employed in construction of an average linkage tree. If one of the three central mtDNA types is the root of the tree, differences in evolutionary rates among the branches become apparent. In particular, the Bushmen appear to have a higher evolutionary rate for mtDNA than the other four populations. Comparisons with nuclear gene frequencies suggest that this higher evolutionary rate may be the product of an elevated mutation rate or fixation of mutations in mtDNA.

Morphine for the relief of breathlessness in patients with chronic heart failure--a pilot study

BACKGROUND

Chronic heart failure (CHF) patients can experience significant breathlessness despite maximum medication for their heart failure. Morphine has long been used to relieve symptoms in acute failure, but there is little evidence about this potentially useful palliative therapy in CHF.

AIMS

To determine the efficacy of morphine for the relief of breathlessness in patients with CHF.

METHOD

Ten out-patients with NYHA III/IV CHF entered a randomised, double-blind, placebo controlled, crossover pilot study. The active arm was 4 days of 5 mg oral morphine four times daily (2.5 mg morphine if creatinine > 200 micromol/l). There were 2 days wash-out between active and placebo arms.

RESULTS

6/10 patients indicated that morphine improved their breathlessness. On morphine, the median breathlessness score fell by 23 mm (P = 0.022) by day 2. The improvement was maintained. Sedation scores increased until day 3 (P = 0.013), reducing on day 4. Four patients developed constipation (P = 0.026). On placebo, there was no significant difference in breathlessness or sedation. One patient had constipation. There were no significant differences in either arm in nausea, quality of life scores, blood pressure, pulse, respiratory rate, or catecholamines. Brain natriuretic peptide fell in both arms; significantly in the morphine arm.

CONCLUSION

Morphine relieves breathlessness due to CHF. A larger study is indicated.

cDNA cloning and expression of a metalloproteinase inhibitor related to tissue inhibitor of metalloproteinases

The purification and characterization of a metalloproteinase inhibitor (MI) from bovine aortic endothelial cells, and the demonstration that it is related to, but distinct from, tissue inhibitor of metalloproteinase (TIMP), have previously been reported [De Clerck, Y. A., Yean, T.-D., Ratzkin, B. J., Lu, H.S. & Langley, K. E. (1989) J. Biol. Chem. 264, 17445-17453]. The cDNA cloning of the bovine MI and its human homolog is now reported. The bovine cDNA cloning used probes designed on the basis of NH2-terminal amino acid sequence of bovine MI. The human cDNA cloning in turn used probes representing parts of the bovine cDNA nucleotide sequence. Both cDNAs encode leader sequences of 26 amino acids and mature protein sequences of 194 amino acids. The amino acid sequences of the mature proteins are 94% identical. The human MI cDNA was expressed in Escherichia coli, and a preparation containing anticollagenase activity was recovered. The amino acid sequence of mature human MI is 38% identical to the sequence for human TIMP, and the 12 cysteines in MI and TIMP are aligned almost identically. Thus MI and TIMP comprise an inhibitor family.

Pancam multispectral imaging results from the Spirit Rover at Gusev Crater

Panoramic Camera images at Gusev crater reveal a rock-strewn surface interspersed with high- to moderate-albedo fine-grained deposits occurring in part as drifts or in small circular swales or hollows. Optically thick coatings of fine-grained ferric iron-rich dust dominate most bright soil and rock surfaces. Spectra of some darker rock surfaces and rock regions exposed by brushing or grinding show near-infrared spectral signatures consistent with the presence of mafic silicates such as pyroxene or olivine. Atmospheric observations show a steady decline in dust opacity during the mission, and astronomical observations captured solar transits by the martian moons, Phobos and Deimos, as well as a view of Earth from the martian surface.

Human mitochondrial manganese superoxide dismutase polymorphic variant Ile58Thr reduces activity by destabilizing the tetrameric interface

Human manganese superoxide dismutase (MnSOD) is a homotetrameric enzyme which protects mitochondria against oxygen-mediated free radical damage. Within each subunit, both the N-terminal helical hairpin and C-terminal alpha/beta domains contribute ligands to the catalytic manganese site. Two identical four-helix bundles, symmetrically assembled from the N-terminal helical hairpins, form a novel tetrameric interface that stabilizes the active sites. The 2.5 A crystallographic structure of the naturally occurring polymorphic variant Ile58Thr MnSOD reveals that the helical hairpin mutation Thr58 causes two packing defects in each of the two four-helix bundles of the tetrameric interface. Similar mutations, expected to cause packing defects in the Cu,ZnSOD dimer interface, are associated with the degenerative disease amyotrophic lateral sclerosis. Ile58Thr MnSOD is primarily dimeric in solution and is significantly less thermostable than the normal enzyme, with decreases of 15 degrees C in the main melting temperature and 20 degrees C in the heat-inactivation temperature. Consequently, this mutant MnSOD is compromised at normal body temperatures: thermal inactivation, predicted from the decrease in thermal stability, occurs with a theoretical half-life of only 3.2 h at 37 degrees C (1.4 h at 41 degrees C), compared with 3.1 years for native MnSOD. This prediction is supported by direct measurements: incubation at 41.7 degrees C for 3 h has no effect on the activity of native MnSOD but completely inactivates mutant MnSOD. Rapid inactivation of Ile58Thr MnSOD at the elevated temperatures associated with fever and inflammation could provide an early advantage by killing infected cells, but also would increase superoxide-mediated oxidative damage and perhaps contribute to late-onset diseases.

Pancam multispectral imaging results from the Opportunity Rover at Meridiani Planum

Panoramic Camera (Pancam) images from Meridiani Planum reveal a low-albedo, generally flat, and relatively rock-free surface. Within and around impact craters and fractures, laminated outcrop rocks with higher albedo are observed. Fine-grained materials include dark sand, bright ferric iron-rich dust, angular rock clasts, and millimeter-size spheroidal granules that are eroding out of the laminated rocks. Spectra of sand, clasts, and one dark plains rock are consistent with mafic silicates such as pyroxene and olivine. Spectra of both the spherules and the laminated outcrop materials indicate the presence of crystalline ferric oxides or oxyhydroxides. Atmospheric observations show a steady decline in dust opacity during the mission. Astronomical observations captured solar transits by Phobos and Deimos and time-lapse observations of sunsets.

Isolated arthroscopic meniscal repair: a long-term outcome study (more than 10 years)

A single surgeon's consecutive series of 50 arthroscopically repaired meniscal tears in 48 patients was retrospectively reviewed. None of these patients had concomitant ligament damage to the knee. The average follow-up period was 10 years, 9 months. Criteria for clinical success included 1) history of pain of grade 1 or less and absence of locking, catching, or giving way; 2) a physical examination demonstrating no significant effusion and a painless and negative jump sign; and 3) no subsequent surgical procedures on the repaired meniscus. Patient satisfaction was quite high, although clinical confirmation was possible in only 38 knees, indicating a clinical success rate of 76%. Bilateral standing radiographs were obtained on these 38 operated knees and were evaluated using Fairbank's classification. Evaluation of the radiographs revealed that 8% of the operated knees had minimal joint changes, as compared with 3% in the contralateral, nonoperated knee. This study demonstrates that arthroscopic meniscal repair in knees with isolated meniscal tears has the potential for a long-term successful clinical and radiographic outcome.

Clinically important differences in the intensity of chronic refractory breathlessness

CONTEXT

Clinically important differences in chronic refractory breathlessness are ill defined but important in clinical practice and trial design.

OBJECTIVES

To estimate the clinical relevance of differences in breathlessness intensity using distribution and patient anchor methods.

METHODS

This was a retrospective data analysis from 213 datasets from four clinical trials for refractory breathlessness. Linear regression was used to explore the relationship between study effect size and change in breathlessness score (0-100mm visual analogue scale) and to estimate the change in score equivalent to small, moderate, and large effect sizes. Pooled individual blinded patient preference data from three randomized controlled trials were analyzed. The difference between the mean change in Day 4 minus baseline scores between preferred and non-preferred arms was calculated.

RESULTS

There was a strong relationship between change in score and effect size (P = 0.001; R(2) = 0.98). Values for small, moderate, and large effects were -5.5, -11.3, and -18.2mm. The participant preference change in score was -9mm (95% CI, -15.8, -2.1) (P = 0.008).

CONCLUSION

This larger dataset supports a clinically important difference of 10mm. Studies should be powered to detect this difference.

Ethnic variation in Hpa 1 endonuclease cleavage patterns of human mitochondrial DNA

The mtDNAs of 235 individuals from five ethnic groups were analyzed for restriction site variation by digestion with restriction endonuclease Hpa I, Southern transfer, and hybridization with 32P-labeled human mtDNA. Six different cleavage patterns (morphs) were found, all of which could be related to each other by single nucleotide substitutions. Differences were found in the frequency of these morphs among the populations. The largest difference observed was in the frequency of the morph most common in Caucasians and Orientals compared to the frequency of that found in Africans. This difference apparently originated by the sequence change G-T-C-A-A-C to G-T-T-A-A-C. This alteration permitted recognition by Hpa I but did not alter the amino acid sequence. Two other observed differences were due to separate substitutions occurring in the ribosomal RNA genes. Comparison with primate data shows that the morph with two fragments, found in 12.5% of Oriental and 4% of Bantu samples, might be the ancestral type common to all hominoids. These two conserved sites were localized in tRNA genes in the anticodon loop. Assuming that the two-fragment morph is ancestral, this finding is consistent with previous data suggesting that Asia is genetically central to the radiations that are thought to have given rise to the human ethnic groups.

Fat embolism syndrome

Since it was initially described, fat embolism syndrome (FES) has remained one of the least clearly understood complications of trauma. This article is a review of the classic and current literature on FES with regard to its causes, pathophysiology, clinical presentation, diagnosis, and treatment. FES is associated with many traumatic and nontraumatic conditions, but is most commonly associated with fractures of long bones of the lower extremity. The pathophysiology is thought to be a cascade of events which can lead to adult respiratory distress syndrome (ARDS). Signs and symptoms of clinical FES usually begin within 24 to 48 hours after trauma. The classic triad involves pulmonary changes, cerebral dysfunction, and petechial rash. Clinical diagnosis is key because laboratory and roentgenographic diagnosis is not specific. Treatment consists of careful initial handling, early stabilization of fractures, careful volume replacement, analgesia, respiratory support, and perhaps steroids. The vast majority of patients today survive FES without sequelae.

Living with breathlessness: a systematic literature review and qualitative synthesis

What is the experience of people living with breathlessness due to medical conditions, those caring for them and those treating them, with regard to quality of life and the nature of clinical interactions?Electronic databases (Ovid MEDLINE, Embase, CINAHL Plus and PsycINFO) were searched (January 1987 to October 2017; English language), for qualitative studies exploring the experience of chronic breathlessness (patients, carers and clinicians). Two independent reviewers screened titles, abstracts and papers retrieved against inclusion criteria. Disagreements were resolved with a third reviewer. Primary qualitative data were extracted and synthesised using thematic synthesis.Inclusion and synthesis of 101 out of 2303 international papers produced four descriptive themes: 1) widespread effects of breathlessness; 2) coping; 3) help-seeking behaviour; and 4) clinicians' responsiveness to the symptom of breathlessness. The themes were combined to form the concept of "breathing space", to show how engaged coping and appropriate help-seeking (patient) and attention to symptom (clinician) helps maximise the patient's quality of living with breathlessness.Breathlessness has widespread impact on both patient and carer and affects breathing space. The degree of breathing space is influenced by interaction between the patient's coping style, their help-seeking behaviour and their clinician's responsiveness to breathlessness itself, in addition to managing the underlying disease.

The prevalence and associated variables of deep venous thrombosis in patients with advanced cancer

The prevalence of venous thromboembolism (VTE) in cancer patients has been estimated as up to 15% antemortem, and higher (over 50% in pancreatic tumours) postmortem owing to the asymptomatic nature of many episodes of VTE. We investigated the prevalence of deep venous thrombosis (DVT) in a population of 298 hospice inpatients with advanced cancer. They were screened for the presence of DVT using light reflection rheography; 258 (86.6%) patients were evaluable for DVT, which was found in 135 (52%; 95% confidence interval 46-58). Factors associated (multivariate analysis) with the presence of DVT were: poor mobility, reduced serum albumin level and higher serum urea. A DVT risk assessment index was calculated using these variables. The three highest categories all had significant rates of DVT and, although the lowest category had a low rate of DVT, it accounted for less than 10% of all patients tested. DVT is common in patients with advanced cancer. It was found to be significantly associated with the above variables, but a combined index was of limited clinical application. In view of the number of patients identified with DVT, repeated small pulmonary emboli may be responsible for more symptoms than previously recognized in cancer patients.

Aerobic microbial growth at low oxygen concentrations

Sterilizable membrane probes were used to study the relation between oxygen concentration and respiration rate in Candida utilis growing on acetate. When the organism was grown in a continuous fermentor at various dissolved oxygen concentrations (0.23 x 10(-6) to 32 x 10(-6)m), with time allowed for full adaptation to each oxygen concentration, the relationship between oxygen concentration and growth rate simulated Michaelis-Menten behavior, giving an apparent K(m) for oxygen of 1.3 x 10(-6)m. When respiration rate was measured at various oxygen concentrations without allowing time for adaptation, it was found that the respiration rate was directly proportional to O(2) concentration at low O(2) concentrations, and independent of O(2) concentration at high O(2) concentrations. Transition from one type of behavior to the other was fairly abrupt. The respiration rate in the presence of excess oxygen depended on the O(2) concentration at which the cells were grown, but the rate at low O(2) concentrations did not. There was evidence that, at low oxygen concentrations, oxygen diffusion through the cell substance limits respiration rate, at least in part.