Longitudinal Associations of Family Relationship Quality with Chronic Pain Incidence and Persistence Among Aging African Americans

OBJECTIVES

This study examines how family relationships convey risk or resilience for pain outcomes for aging African Americans, and to replicate and extend analyses across two nationally representative studies of aging health.

METHOD

African American participants in Midlife in the United States (MIDUS, N = 755) and the Health and Retirement Study (HRS, N = 2585) self-reported chronic pain status at 2006 waves and then again 10 years later. Logistic regression was used to estimate the odds of pain incidence and persistence explained by family, intimate partner, and parent-child strain and support, as well as average support and average strain across relationships.

RESULTS

On average, MIDUS participants were younger (M = 52.35, SD = 12.06; 62.1% female) than HRS (M = 66.65, SD = 10.92; 63.7% female). Family support and average support were linked to a decreased odds of pain incidence in MIDUS, but only when tested without accounting for strain, while parent-child strain was a risk factor for pain incidence in HRS, as was average strain. Family support protected against pain persistence in MIDUS, while average support was linked to a reduced odds of pain persisting in HRS.

DISCUSSION

Chronic pain outcomes are worse for African Americans for a number of reasons, but parent-child strain may contribute to the risk of new pain developing over time for older adults. Conversely, family support may offer a protective benefit for pain incidence and persistence among aging African Americans. Findings implicate family relationships as a potential target of pain management interventions.

Training to use smart tablets to access reliable online health information in older adults' post-pandemic: A focused pilot intervention study

BACKGROUND

Older adults are becoming more accepting and interested in using digital technologies, but difficulties and barriers remain for accessing reliable health-related information. The purpose of this focused pilot intervention study was to: (1) understand older adults' firsthand experiences and challenges while using smart tablets post-COVID-19 pandemic, and (2) gather suggestions for age-appropriate training materials, preference of training materials, and resources to access reliable online health information.

METHODS

A focused pilot intervention study that involved training older adults to use smart tablets followed by focus group of a convenience sample of 13 older adults (65-85 years old; 91.6% female) on their experiences of using smart tablets.

RESULTS

Thematic analysis revealed three themes: tablets are convenient to access online information and older adults reported technical, security concerns, emotional and cognitive challenges regarding use of smart tablets. Older adults also requested one-on-one support, assistance, and topic specific learning for future training sessions.

CONCLUSIONS

Future studies should focus on providing detailed, clear instructions at an acceptable pace for older adults.

A descriptive study of physical function and performance in older black men with low back pain

The purpose of this paper is to describe physical function and performance scores and examine the relationships between measures of physical performance in older Black men with low back pain. The Mobility, Aging, Pain, and Disparities study used a cross-sectional, observational design to objectively measure physical performance on the Short Physical Performance Battery (SPPB), the Back Performance Scale (BPS), and the 400-meter Walk Test along with subjective ratings of pain intensity in the past 24 hours. Sixty community-based Black men aged 61-87 (x̄= 70 ± 6) years had an average BPS score of 7.0 ± 4 and total score on the SPPB 8.5 ± 2.1. Average 400-meter Walk time was 6.3 ± 3.1 minutes. Men's average pain intensity in the past 24 hours was 5.7 ± 2, indicating moderate pain. In conclusion, older Black men with low back pain demonstrated low physical function scores and a higher level of disability.

Elucidating factors contributing to disparities in pain-related experiences among adults with or at risk for knee osteoarthritis

Background and purpose

We and others have reported ethnic/race group differences in clinical pain, physical function, and experimental pain sensitivity. However, recent research indicates that with consideration for socioenvironmental factors, ethnicity/race differences become less or non-significant. Understanding of factors contributing to pain inequities are needed. Guided by the NIA and NIMHD Health Disparities Research Frameworks, we evaluate the contributions of environmental and behavioral factors on previously reported ethnic/race group differences in: (1) clinical pain, (2) physical function, and (3) experimental pain in individuals with knee pain.

Methods

Baseline data from Understanding of Pain and Limitations in Osteoarthritis Disease (UPLOAD) and UPLOAD-2 studies were analyzed. Participants were adults 45 to 85 years old who self-reported as non-Hispanic white (NHW) or black (NHB) with knee pain. A health assessment and quantitative sensory testing were completed. Sociodemographics, environmental, health, clinical and experimental pain, and physical functioning measures were included in nested regressions.

Results

Pooled data from 468 individuals, 57 ± 8 years of age, 63% women, and 53% NHB adults. As NHB adults were younger and reported greater socioenvironmental risk than the NHW adults, the term sociodemographic groups is used. With inclusion of recognized environmental and behavioral variables, sociodemographic groups remained a significant predictor accounting for <5% of the variance in clinical pain and physical function and <10% of variance in experimental pain.

Conclusion

The incorporation of environmental and behavioral factors reduced relationships between sociodemographic groups and pain-related outcomes. Pain sites, BMI, and income were significant predictors across multiple models. The current study adds to a body of research on the complex array of factors contributing to disparities in pain-related outcomes.

CE: Assessing Movement-Evoked Pain

ABSTRACT

One of the most common and nuanced tasks that nurses perform is pain assessment, particularly in acute postoperative settings where frequent reassessments are needed. Most assessments are limited to obtaining a pain intensity score with little attention paid to the conditions necessitating the assessment or the factors contributing to the pain. Pain is frequently assessed during rest, but seldom during periods of movement or activity, which is a crucial omission given that acute postoperative movement-evoked pain (MEP) is intense and a common barrier to healing and restoration of function. In addition to physical limitations, MEP can impede cognitive, emotional, and social functioning in ways that can contribute to chronic pain, mood disorders, and disability. Professional and regulatory standards are moving away from a focus on pain intensity to an emphasis on its context, impact on function, and associated distress. Thus, there are many driving forces compelling nurses to integrate MEP assessments into practice to expedite the restoration of biopsychosocial functioning in postoperative patients. The authors discuss the clinical significance of a MEP assessment as well as protocols and tools for completing such assessments.

Is Resilience Protective of Movement-Evoked Pain in Older Black Women Who Experience Discrimination?

Older non-Hispanic black (NHB) individuals experience greater pain and more frequent experiences of perceived discrimination compared to non-Hispanic white individuals with knee osteoarthritis. The current study explored whether being resilient buffers against movement-evoked pain (MEP) in NHB women who report everyday experiences of discrimination. In a secondary analysis of the Understanding Pain and Limitations in Osteoarthritic Disease (UPLOAD-2) study, data were collected at the University of Florida and the University of Alabama at Birmingham. Participants were 58 community-dwelling older women who self-identified as NHB and reported knee osteoarthritis. Participants completed the Brief Resilience Scale, a self-report measure of trait resilience. MEP was assessed following the Short Physical Performance Battery. Moderation analyses were conducted to investigate whether resilience moderates the association between experiences of discrimination and MEP. Study site, age, body mass index, and income were included as covariates. Overall, neither everyday experiences of discrimination (b=.292, 95% confidence interval [CI]=-.415 to 1.000) nor trait resilience was associated with MEP (b=-11.540, 95% CI=-23.583 to .503). However, there was a significant interaction (b=1.037, 95% CI=.150 to 1.925) between experiences of discrimination and trait resilience in predicting MEP. Simple slopes analysis revealed that lower discrimination was associated with lower MEP, but only in women who reported high levels of resilience (b=1.100, p=.014), but this protective effect of resilience was absent in women reporting high discrimination. Our findings suggest that as discrimination increases, the protective effects of resilience on movement evoked-pain decreases. Therefore, high trait resilience may be protective when experiences of discrimination are low.

A Preliminary Measurement and Understanding of Movement-Evoked Pain in African American Elder Adults

Osteoarthritis (OA) is a principal cause of disabling knee pain, and movement is a known exacerbator of pain in African Americans (AAs). Still, research has neglected to understand the relationship between pain with movement and its impact on function and mobility. Our previous study found significantly higher movement-evoked pain between AAs and White American (WAs). Therefore, this case-control observational study investigated inter-racial and intra-racial differences in movement-evoked pain in AAs and WAs (N= 28) who were 55-78 years-of-age (M= 65.75, SD= 6.23). We measured pain intensity (0-10) pre/ante/post multiple performance-based functional activities; we report preliminary results for 7-meter GAITRite® walk and Stair climbs. Pain intensity was higher before and after the 7-meter walk and stair climbs in AAs, although not significantly different than WAs. We will conduct additional statistical tests for the remaining functional activities to identify potential differences and ethnic-specific factors that distinguish movement-evoked pain and function by race.

Pain and Its Management: Strategies and Outcomes in Older Adults With or at Risk for Knee Osteoarthritis

Knee osteoarthritis (KOA) is a leading cause of mobility disability that is characterized by chronic pain among older adults. Non-Hispanic Blacks (NHBs) suffer disproportionately from non-Hispanic Whites (NHWs), reporting higher pain intensity and disability. It is unclear how these differences in symptomatology translate into different patterns of utilization for self-management (SM) of pain, and if such patterns are associated with underlying biological pain mechanisms. This multisite observational study examined (1) use of self-management strategies among older NHB and NHW adults with/at risk for KOA and (2) associations among self-management strategies, clinical and experimental pain. After approval from institutional IRBs, NHB and NHW older adults (N= 202) with knee pain completed the McGill Pain Questionnaire-Short Form, questions on treatment strategies (e.g., massage, ice, heat, medications), and quantitative sensory testing. Covariates included study site and education. On average, participants reported using 2 ± 1.65 SM strategies, with 79% endorsing at least one SM strategy. Analysis of covariance revealed that clinical pain differed by race/ethnicity and use of SM and/or medical treatments (p’s < 0.01). SM use did not differ by race/ethnicity, p = 0.15, but did differ significantly by gender, p < 0.05. Multiple linear regression demonstrated significant positive associations between SM and heat pain sensitivity for both NHBs and NHWs, (p < 0.05). SM is an important component of OA management for NHBs and NHWs. Our study is one of the first to show that SM use is significantly associated with pain mechanisms. Improved understanding will facilitate better mechanism-targeted pain management.

Uncovering the Influence of Psychosocial Factors on Pain-Related Brain Responses in Older Adults With Chronic Pain

Psychosocial factors such as experiences of discrimination, pain catastrophizing and perceived stress are associated with poor osteoarthritis-related pain and disability outcomes across sex and ethnic/race groups. However, the mechanisms that mediate these psychosocial factors and knee osteoarthritis outcomes across race and sex are unclear. A cross-sectional correlational design identified the associations between everyday discrimination and clinical pain, disability and functional performance among 188 non-Hispanic Black (NHB) and non-Hispanic White (NHW) persons with knee osteoarthritis. In a serial mediated model, perceived stress and pain catastrophizing mediated the relationship between discrimination and osteoarthritis-related outcome variables in female participants. Using magnetic resonance imaging, findings suggest that experiences of discrimination differentially affect structural brain regions based on both race/ethnicity and sex in older adults with knee osteoarthritis. Given this, we are also currently investigating the extent to which pain catastrophizing on pain-related brain structure differs across race/ethnic groups in older adults with knee osteoarthritis.

Patterns and Perceptions of Self-Management for Osteoarthritis Pain in African American Older Adults

OBJECTIVE

To explore and describe older African Americans' patterns and perceptions of managing chronic osteoarthritis pain.

METHODS

A convergent parallel mixed-methods design incorporating cross-sectional surveys and individual, semistructured interviews.

SETTING

One hundred ten African Americans (≥50 years of age) with clinical osteoarthritis (OA) or provider-diagnosed OA from communities in northern Louisiana were enrolled.

RESULTS

Although frequency varied depending on the severity of pain, older African Americans actively used an average of seven to eight self-management strategies over the course of a month to control pain. The average number of self-management strategies between high and low education and literacy groups was not statistically different, but higher-educated adults used approximately one additional strategy than those with high school or less. To achieve pain relief, African Americans relied on 10 self-management strategies that were inexpensive, easy to use and access, and generally perceived as helpful: over-the-counter (OTC) topicals, thermal modalities, land-based exercise, spiritual activities, OTC and prescribed analgesics, orthotic and assistive devices, joint injections, rest, and massage and vitamins.

CONCLUSIONS

This is one of the first studies to quantitatively and qualitatively investigate the self-management of chronic OA pain in an older African American population that happened to be a predominantly higher-educated and health-literate sample. Findings indicate that Southern-dwelling African Americans are highly engaged in a range of different self-management strategies, many of which are self-initiated. Although still an important component of chronic pain self-management, spirituality was used by less than half of African Americans, but use of oral nonsteroidal anti-inflammatory drugs and opioids was relatively high.

Exploring Associations Between Metabolites and Symptoms of Fatigue, Depression and Pain in Women With Fibromyalgia

Fibromyalgia (FM) is a chronic noncommunicable disorder characterized by a constellation of symptoms that include fatigue, depression and chronic pain. FM affects 2%-8% of the U.S. population, 2% of the global population, with 61%-90% of FM diagnoses attributed to women. Key causal factors leading to the development and severity of FM-related symptoms have not yet been identified. The purpose of this article is to report relationships among identified metabolites and levels of fatigue, depression, pain severity, and pain interference in a sample of 20 women with FM. In this secondary analysis, we conducted global metabolomic analysis and examined the data for relationships of metabolite levels with self-reported symptoms of fatigue, depression, pain severity, and pain interference. Results revealed six metabolites (6-deoxy-hexose; pantothenic acid; ergothioneine; l-carnitine; n-acetylserotonin; butyrobetaine) and their associated metabolic pathways such as carnitine synthesis, lipid oxidation, tryptophan metabolism, beta-alanine metabolism and pantothenic and Coenzyme-A biosynthesis that were either positively or inversely related to pain severity, pain interference, or both. The preliminary data presented suggest that metabolites representing energy, amino acid, or lipid classification may be associated with pain symptom severity and interference in women with FM. Future work will confirm these findings in a large, comparative cohort, targeting metabolites and metabolite pathways to better understand the relationships of metabolites and symptomology.

Abstract C003: Sociodemographic and clinical characteristics associated with worst pain intensity among cancer patients

Introduction: Approximately 70% of individuals living with cancer experience persistent pain. Previous studies showed racial/ethnic differences existing across various cancer-related outcomes. Yet, few studies have examined the racial/ethnic differences in worst pain intensity among cancer patients. Thus, the goal of this secondary data analysis was to identify predictors of worst pain intensity, including race/ethnicity, and cancer stage in a diverse sample. Methodology: A convenience sample of cancer patients (N=1,516) recruited from cancer centers in the Western and Midwestern United States completed questionnaires collecting demographic, chronic pain, and cancer-specific information. In addition to race and ethnicity, covariates for the linear regression included: other demographic characteristics, tumor stage, cancer type, cancer stage, and substance use. The study outcome, worst pain intensity, was measured on 0 (no pain) to 10 (worst pain) scale and was captured using a validated modified McGill Pain Questionnaire (PAINReportIt). A multinomial generalized linear regression model was utilized to determine associations between selected predictors and pain intensity. Statistical significance was considered at p&lt; .05. Results: Our study sample was predominantly White (65.0%), Black (24.1%), and Other (10.9%). On average, participants were 58.9 (SD=14.1) years old. Additionally, participants reported a 5.9 (SD=3.0) worst pain intensity score. Selected significant covariates: being non-Hispanic Black (β=0.67; P= 0.002), belonging to an Other racial group (β= 1.04; P= 0.0004), earning less than $10,000 annually (β=0.77; P= 0.0151), earning between $10,000 - $50,000 annually (β= 0.85; P= 0.0038), having toothache pain (β=0.12; P= 0.0004), and having stage 4 cancer (β=0.82; P= 0.0007) were positively associated with worse cancer pain. Conclusion: Our analysis suggests that being non-Hispanic Black, a member of an other racial group, low socioeconomic status, having had toothache pain, and having advanced stage cancer are significant predictors of worst pain intensity among cancer patients. Future studies focused on the management of cancer-related pain should target under-resourced individuals and those with advanced cancer for pain prevention strategies to prevent the escalation of pain intensity. Additionally, future studies should continue to oversample underrepresented Black populations in order to continue assessing disparities in clinical cancer outcomes.

Citation Format: Verlin Joseph, Keesha Roach, Staja Booker, Jinhai Huo, Yingwei Yao, Xinguang Chen, Robert L Cook, Diana J Wilkie. Sociodemographic and clinical characteristics associated with worst pain intensity among cancer patients [abstract]. In: Proceedings of the Twelfth AACR Conference on the Science of Cancer Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; 2019 Sep 20-23; San Francisco, CA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2020;29(6 Suppl_2):Abstract nr C003.

Black American older adults' motivation to engage in osteoarthritis treatment recommendations for pain self-management: A mixed methods study

BACKGROUND

Osteoarthritis is a long-term condition, and four core treatments are recommended to minimize the interference of pain and symptoms on their daily function. However, older Black Americans have traditionally been at a disadvantage in regard to knowledge of and engagement in chronic disease self-management and self-care. Surprisingly, minimal research has addressed understanding motivational factors key to self-management behaviors. Thus, it is important to understand if older Black Americans' self-management is supported by current recommendations for the management of symptomatic osteoarthritis and what factors limit or motivate engagement in recommended treatments.

OBJECTIVE

Our objectives are to: (1) identify stage of engagement in four core recommended treatments for osteoarthritis, (2) describe the barriers and motivators to these recommended treatments, and (3) construct an understanding of the process of pain self-management motivation.

DESIGN

A mixed-methods concurrent parallel design.

SETTING

Participants were recruited from communities in northern Louisiana, USA.

PARTICIPANTS

Black Americans (≥50 years of age) with clinical osteoarthritis and/or provider-diagnosed osteoarthritis were enrolled. One hundred ten participants completed the study, and 18 of these individuals were also interviewed individually.

METHODS

Data were collected using in-person surveys and interviews. Over a period of 11 months, close- and open-ended surveys and in-depth interviews were conducted with participants. Descriptive statistics describe utilization/engagement level as well as barriers and motivators of recommended treatments for non-surgical osteoarthritis. Content and thematic analyses of interviews summarized perspectives on the process and role of motivation in pain self-management.

RESULTS

Overall, engagement levels in treatments ranged from very low to high. Over 55% of older Black Americans were actively engaged in two of the recommended treatments: land-based exercise and strength training. Major motivators included reduction in pain and stiffness and maintenance of mobility and good health. The majority of participants were not using water-based exercise and self-management education. Primary barriers were lack of access, time, and knowledge of resources.

CONCLUSIONS

In order to maximize the benefits of osteoarthritis pain self-management, older Black Americans must be equipped with the motivation, resources, information and skills, and time to engage in recommended treatment options. Their repertoire of behavioral self-management did not include two key treatments and is inconsistent with what is recommended, predominantly due to barriers that are difficult to overcome. In these cases, motivation alone is not optimal in promoting self-management. Providers, researchers, and community advocates should work collaboratively to expand access to self-management resources, particularly when personal and community motivation are high.

OH, YOU JUST GOT ARTHRITIS: OLDER AFRICAN AMERICANS LACK FAMILIAL, SOCIAL, AND PROVIDER SUPPORT FOR PAIN MANAGEMENT

Self-management support from family, friends, and providers is a crucial element in controlling osteoarthritis pain. 110 African-Americans (50-94 years) were surveyed regarding social and provider self-management support, and 18 of the African-American participants were also individually interviewed. This mixed-methods analysis unveiled that 77% were not receiving familial/social or provider support, and a conventional qualitative content analysis confirmed the lack of expected support for self-management with sentiments such as “I’m doin’ this all on my own.” Nonetheless, older African-Americans respected providers’ professional opinion, and 82% believed that treatment from a provider would be helpful. They desired more education and treatment options because they “need somebody to help with these joints and muscles”. However, participants were forced to learn how to care for osteoarthritis pain: “I was taking pain medication, but when I went to the doctor last time he told me to stop… Told me to deal with it [pain].”

PSYCHOSOCIAL AND CULTURAL PAIN EXPERIENCES AND SELF-MANAGEMENT ACROSS DIVERSE OLDER ADULT POPULATIONS

Racial/ethnic minority older adults experience a disproportionate burden of functionally-disabling chronic pain. However, minimal research in pain and aging has fully explicated the unique and endemic psychosocial and cultural factors that strongly influence appraisal, communication, and management/coping of pain. Yet, to fully engage with and care for diverse racial/ethnic older adults, intentional responsiveness to these factors is necessary. This symposium features under-represented racial/ethnic older adult populations and multiple methodologies, including advanced imaging techniques, to understand various psychosocial and cultural factors associated with chronic pain. Our first presenter, Dr. Lor, uses qualitative inquiry to examine pain-associated language and expression of pain in Hmong older adults, which is often laden with stress and misunderstanding. Following is Dr. Taylor who will discuss the mediating effect of stress and coping on bodily pain in inner-city Black older adults. Dr. Terry will present novel findings on the association between catastrophizing (i.e., negative cognitive and emotional response to actual or anticipated pain resulting in feelings of helplessness) and brain structure in non-Hispanic Black and White adults with or at high-risk for knee osteoarthritis pain. This presentation will segway into culturally-relevant pain self-management practices and the role of social support specifically for Blacks from urban Detroit, as presented by Dr. Janevic. We will conclude with Dr. Booker presenting mixed-level data on the lack of familial and social networks and provider support for osteoarthritis pain self-management in Southern-dwelling older Blacks. This symposium extends the knowledge on the nuanced complexity of biopsychosocial and cultural dynamics underlying the pain experience.

SPIRITUALITY IN CHRONIC PAIN SELF-MANAGEMENT: LOWER USE BUT EQUAL IMPORTANCE IN OLDER AFRICAN AMERICANS

Spirituality is a key social determinant of health for African Americans (AAs) and strongly impacts management of chronic pain. Older AAs (average age 68± 12.37) from urban and rural communities completed questionnaires (N= 110) and audio-recorded, semi-structured individual interviews (N= 18) describing osteoarthritis pain self-management. Prayer was used by 42% of AAs, with substantially fewer attending church (23.6%), watching religious television or reading the Bible/Christian literature (20.9%), listening to gospel music (18.2%), and laying of hands (8.2%). Interestingly, prayer and church attendance were the only pain strategies rated by more participants as very helpful. Regardless of religiosity, most AAs believed that spirituality was “an important aspect, whether we realize it always or not”. Specifically, prayer was considered “number one… ‘cause I know it’s gonna be all right once I do pray…prayer help heal the pain”. Spiritual strategies remain integral for chronic pain self-management despite lower than expected use among AAs.

Movement-evoked pain, physical function, and perceived stress: An observational study of ethnic/racial differences in aging non-Hispanic Blacks and non-Hispanic Whites with knee osteoarthritis

BACKGROUND

Knee osteoarthritis (OA) is a pervasive musculoskeletal condition, often exacerbated by movement-evoked pain (MEP). Despite established research demonstrating significant racial differences in OA pain, few studies have investigated ethnic/racial group differences in MEP and lower extremity function and their association with psychosocial factors, such as perceived stress. Therefore, the primary aims were: (1) to identify ethnic/racial group differences in persons with or at risk for knee OA pain based on MEP, physical performance, and perceived stress measures, and (2) to determine if perceived stress explains the relationship between MEP and function in non-Hispanic Blacks (NHBs) and non-Hispanic Whites (NHWs).

METHODS

A total of 162 NHB and NHW community-dwelling older adults (50-78 years of age) were included in this analysis from the Understanding Pain and Limitations in Osteoarthritic Disease (UPLOAD) cross-sectional cohort study. Demographic, anthropometric, pain and functional parameters were assessed using a battery of validated instruments. Descriptive statistics, parametric, and multivariate analyses were conducted to determine ethnic/racial differences in perceived stress, MEP, and function.

RESULTS

Our results support the hypothesis that among persons with knee OA pain, NHBs have significantly greater MEP and lower functional level, despite similar levels of perceived stress. However, perceived stress was more strongly related to MEP in NHB compared to NHWs. Differences in function were limited to walking speed, where NHWs demonstrated faster gait speed.

CONCLUSIONS

Our cross-sectional study demonstrated important ethnic/racial differences in MEP and function. Also, perceived stress had a stronger effect on MEP in NHBs, suggesting that perceived stress may more strongly influence pain with physical movement among NHB adults. MEP may be a clinically important pain outcome to measure in persons with OA, and these data warrant future research on the impact of stress on pain and functional outcomes in older adults, particularly in NHBs.

Empowered to change: evidence from a qualitative exploration of a user-informed psycho-educational programme for people with type 1 diabetes

OBJECTIVES

To evaluate the impact of a user-informed psycho-educational programme for people with type 1 diabetes.

METHODS

Qualitative data derived from repeated interviews and diaries enabled an appraisal of participants' unique, individual experiences.

RESULTS

Thematic analysis elicited a number of themes from each type of data (interview and diaries) which bore similarities in their representation of a process whereby change was desired, solutions were found to bring about that change, and then the process was planned or embarked upon.

DISCUSSION

The acquisition of trustworthy information and a repertoire of coping skills accompanied by regular contact with other people with type 1 diabetes meant that participants achieved an increased sense of control in their lives and were empowered to change.

Vulval punch biopsies: what is the experience of patients and do they alter management?

A questionnaire was used to assess the use of vulval punch biopsies with regard to patient acceptance, complications and relevance to management in patients attending the Oxford vulval clinic over a period of 1 year. All were satisfied with the reasons given for the biopsy. The majority (70%) found the injection of the local anaesthetic to be the most painful part of the procedure. Only minimal bleeding continued after the biopsy in a third of patients and stopped spontaneously within a few hours. None of the patients had secondary infection or chronic ulceration. The most common diagnosis confirmed by biopsy at the Oxford vulval clinic was lichen sclerosus (LS) and the mean age of patients was 63.6 years. Although no malignancy was diagnosed in our patients, in view of potential for malignancy and the lack of significant side effects associated with the procedure, we would recommend that punch biopsies be performed if LS is suspected.

Nuclear localization of Dpc4 (Madh4, Smad4) in colorectal carcinomas and relation to mismatch repair/transforming growth factor-beta receptor defects

The tumor-suppressor protein Dpc4 (Smad4, Madh4) regulates gene expression. On binding of an extracellular ligand of the extensive transforming growth factor (TGF) superfamily to its cognate receptor complex, latent cytoplasmic Dpc4 is activated and translocated into the nucleus to function as part of various DNA-binding transcriptional activator complexes. The most relevant ligand/receptor pair to control the tumor suppressive function of Dpc4 remains uncertain, but is usually assumed to be TGF-beta and its heteromeric receptor. We exploited a fortuitous experiment of nature to directly test this hypothesis: the TGF-beta type II receptor gene is inactivated by mutation in nearly all colorectal carcinomas having microsatellite instability, as seen in hereditary nonpolyposis colorectal cancer (HNPCC) and in sporadic medullary colorectal cancers. Using a specific and sensitive immunohistochemical label for Dpc4, we examined nuclear localization of Dpc4 in 13 HNPCC, six medullary, and 41 sporadic nonmedullary colorectal carcinomas. In agreement with published rates, two (5%) of 41 sporadic tumors showed complete loss of Dpc4 protein, indicative of genetic inactivation. All 13 HNPCC and six medullary tumors had intact cytoplasmic and nuclear Dpc4 localization. The TGFBR2 gene was sequenced in three of the cancers from patients with HNPCC, and all of these harbored inactivating mutations. The specificity of the immunohistochemical assay was demonstrated in xenograft tumors of syngeneic cell lines that differed in DPC4 genetic status because of an engineered gene knockout. Thus, nuclear localization of Dpc4 can be maintained in cells with inactivated TGF-beta type II receptors, suggesting the persistence of tumor-suppressive action of an upstream signaling input, most likely a ligand/receptor complex distinct from TGF-beta. Identification of the relevant input would be expected to have implications for the understanding of tumorigenesis and the design of rational biological therapy.

Lysine 2,3-aminomutase and trans-4,5-dehydrolysine: characterization of an allylic analogue of a substrate-based radical in the catalytic mechanism

An analogue of lysine, trans-4,5-dehydro-L-lysine (trans-4, 5-dehydrolysine), is a potent inhibitor of lysine 2,3-aminomutase from Clostridium subterminale SB4 that competes with L-lysine for binding to the active site. Inclusion of trans-4,5-dehydrolysine with activated enzyme and the coenzymes pyridoxal-5'-phosphate and S-adenosylmethionine, followed by freezing at 77 K, produces an intense signal in the electron paramagnetic resonance (EPR) spectrum at g 2.0, which is characteristic of an organic radical. A series of deuterated and (15)N-labeled samples of trans-4,5-dehydrolysine were synthesized and used to generate the EPR signal. Substitution of deuterium for hydrogen at C2, C3, C4, C5, and C6 of trans-4, 5-dehydrolysine led to significant simplifications and narrowing of the EPR signal, showing that the unpaired electron was located on the carbon skeleton of 4,5-trans-4,5-dehydrolysine. The hyperfine splitting pattern is simplified by use of 4,5-dehydro[3, 3-(2)H(2)]lysine or 4,5-dehydro[4,5-(2)H(2)]lysine, and it is dramatically simplified with 4,5-dehydro-[3,3,4,5,6,6-(2)H(6)]lysine. Spectral simulations show that the EPR signal arises from the allylic radical resulting from the abstraction of a hydrogen atom from C3 of trans-4,5-dehydrolysine. This radical is an allylic analogue of the substrate-related radical in the rearrangement mechanism postulated for this enzyme. The rate constant for formation of the 4,5-dehydrolysyl radical (2 min(-)(1)) matches that for the decrease in the concentration of [4Fe-4S](+), showing that the two processes are coupled. The cleavage of S-adenosylmethionine to 5'-deoxyadenosine and methionine takes place with a rate constant of approximately 5 min(-)(1). These kinetic correlations support the hypothesis that radical formation results from a reversible reaction between [4Fe-4S](+) and S-adenosylmethionine at the active site to form [4Fe-4S](2+), the 5'-deoxyadenosyl radical, and methionine as intermediates.

Phenotypic and molecular characteristics of hyperplastic polyposis

BACKGROUND & AIMS

Patients with hyperplastic polyposis are reported to have multiple and/or large hyperplastic polyps (HPs) and an increased risk of colorectal cancer, but the phenotype and genetic alterations in hyperplastic polyposis have not been studied in detail.

METHODS

We evaluated clinical-pathological and molecular characteristics of 129 HPs, 6 serrated adenomas, and 3 admixed hyperplastic-adenomatous polyps from 13 patients with hyperplastic polyposis (more than 20 HPs), 5 patients with a large HP (>/=1 cm in diameter), and 5 patients with multiple HPs (5-10 HPs).

RESULTS

HPs in the right colon in contrast to the left colorectum had more frequent topographic dysregulation of p21(Waf-1/Cip1) expression (94% vs. 76%, P = 0.03) and of proliferation (92% vs. 53%, P = 0. 0001), but less frequent allelic loss of chromosome 1p (4% vs. 17%, P = 0.03). K-ras mutation was present in 8% of HPs, p53 gene product overexpression in none, and microsatellite instability in 3% without relationship to microsatellite instability in synchronous cancer. Patients with a large HP differed from those with multiple HPs in having a high frequency of right-sided HP (63% vs. 22%, P = 0.01) and of right-sided colon cancer (100% vs. 8%, P = 0.003). Hyperplastic polyposis was associated with a family history of colorectal cancer (P = 0.01) and with loss of chromosome 1p in HP (21% vs. 0%, P = 0.001).

CONCLUSIONS

A hyperplastic polyp/dysplasia-to-adenocarcinoma sequence can be manifested in 3 distinct phenotypes consisting of patients with hyperplastic polyposis and chromosome 1p allelic loss in some HPs, in contrast to patients who have large, right-sided HPs or small numbers of HPs that lack 1p loss.

Alternative tests make the grade

Toxicity testing is absolutely necessary for assessing the safety of substances in food, air, and water, in the workplace and at home. Although there are several tried-and-true toxicity assays, the search is always on for methods that can even better predict toxic effects. As scientific understanding of the effects of environmental toxicants grows, new tests are needed to evaluate previously unexamined end points and to take advantage of advances in biotechnology and the growing knowledge of how toxicants work at the molecular and cellular levels. Another issue is how to develop tests that can reliably and accurately assess toxicity using less time, money, and materials, and with greater regard for animal welfare. The Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) was established in 1997 to address these needs through the development, validation, acceptance, and harmonization of new and revised toxicological test methods throughout the federal government.

Studies on the catalysis of carbon-cobalt bond homolysis by ribonucleoside triphosphate reductase: evidence for concerted carbon-cobalt bond homolysis and thiyl radical formation

Ribonucleotide reductases (RNRs) catalyze the rate-determining step in DNA biosynthesis: conversion of nucleotides to deoxynucleotides. The RNR from Lactobacillus leichmannii utilizes adenosylcobalamin (AdoCbl) as a cofactor and, in addition to nucleotide reduction, catalyzes the exchange of tritium from [5'-3H]-AdoCbl with solvent. Examination of this exchange reaction offers a unique opportunity to investigate the early stages in the nucleotide reduction process [Licht S. S., Gerfen, G. J., and Stubbe, J. (1996) Science 271, 477-481]. The kinetics of and requirements for this exchange reaction have been examined in detail. The turnover number for 3H washout is 0.3 s-1, and it requires an allosteric effector dGTP (Km = 17 +/- 3 microM), AdoCbl (Km = 60 +/- 9 microM) and no external reductant. The effects of active-site mutants of RTPR (C119S, C419S, C731S, C736S, and C408S) on the rate of the exchange reaction have been determined, and only C408 is essential for this process. The exchange reaction has previously been monitored by stopped-flow UV-vis spectroscopy, and cob(II)alamin was shown to be formed with a rate constant of 40 s-1 [Tamao, Y., and Blakley, R. L. (1973) Biochemistry 12, 24-34]. This rate constant has now been measured in D2O, with [5'-2H2]-AdoCbl in H2O, and with [5'-2H2]-AdoCbl in D2O. A comparison of these results with those for AdoCbl in H2O revealed kH/kD of 1.6, 1.7, and 2.7, respectively. The absolute amounts of cob(II)alamin generated with [5'-2H2]-AdoCbl in D2O in comparison with AdoCbl in H2O reveal twice as much cob(II)alamin in the former case. Similar transient kinetic studies with C408S RTPR reveal no cob(II)alamin formation. These experiments allow proposal of a minimal mechanism for this exchange reaction in which RNR catalyzes homolysis of the carbon-cobalt bond in a concerted fashion, to generate a thiyl radical on C408, cob(II)alamin, and 5'-deoxyadenosine.

Accumulated clonal genetic alterations in familial and sporadic colorectal carcinomas with widespread instability in microsatellite sequences

A subset of hereditary and sporadic colorectal carcinomas is defined by microsatellite instability (MSI), but the spectra of gene mutations have not been characterized extensively. Thirty-nine hereditary nonpolyposis colorectal cancer syndrome carcinomas (HNPCCa) and 57 sporadic right-sided colonic carcinomas (SRSCCa) were evaluated. Of HNPCCa, 95% (37/39) were MSI-positive as contrasted with 31% (18/57) of SRSCCa (P < 0.000001), but instability tended to be more widespread in SRSCCa (P = 0.08). Absence of nuclear hMSH2 mismatch repair gene product by immunohistochemistry was associated with germline hMSH2 mutation (P = 0.0007). The prevalence of K-ras proto-oncogene mutations was similar in HNPCCa and SRSCCa (30% (11/37) and 30% (16/54)), but no HNPCCa from patients with germline hMSH2 mutation had codon 13 mutation (P = 0.02), and two other HNPCCa had multiple K-ras mutations attributable to subclones. 18q allelic deletion and p53 gene product overexpression were inversely related to MSI (P = 0.0004 and P = 0.0001, respectively). Frameshift mutation of the transforming growth factor beta type II receptor gene was frequent in all MSI-positive cancers (85%, 46/54), but mutation of the E2F-4 transcription factor gene was more common in HNPCCa of patients with germline hMSH2 mutation than in those with germline bMLH1 mutation (100% (8/8) versus 40% (2/5), P = 0.04), and mutation of the Bax proapoptotic gene was more frequent in HNPCCa than in MSI-positive SRSCCa (55% (17/31) versus 13% (2/15), P = 0.01). The most common combination of mutations occurred in only 23% (8/35) of evaluable MSI-positive cancers. Our findings suggest that the accumulation of specific genetic alterations in MSI-positive colorectal cancers is markedly heterogeneous, because the occurrence of some mutations (eg, ras, E2F-4, and Bax genes), but not others (eg, transforming growth factor beta type II receptor gene), depends on the underlying basis of the mismatch repair deficiency. This genetic heterogeneity may contribute to the heterogeneous clinical and pathological features of MSI-positive cancers.

Molecular detection of genetic alterations in the serum of colorectal cancer patients

We have searched for the presence of genetic alterations in serum DNA obtained from 44 colorectal cancer patients. Microsatellite analysis using highly polymorphic markers revealed loss of heterozygosity and/or microsatellite instability in 35 of 44 (80%) primary tumors. No alterations were detected in the paired serum DNA. We next used an oligonucleotide-mediated mismatch ligation assay to detect tumor specific gene mutations in the serum. Among the 16 cases with a K-ras gene mutation in the tumor, the same mutation was detected in three paired serum samples. In the 10 cases with a p53 mutation in the tumor, the identical mutation was detected in seven corresponding serum samples. Comparison of the molecular analysis with clinical diagnosis of these patients revealed that none of the seven Dukes' stage B patients with a K-ras mutation in their tumors demonstrated a mutation in the serum. In contrast, five of seven stage B patients with a p53 mutation in the tumor demonstrated a mutation in the paired serum (P = 0.01, Fisher's exact test). Taken together, either a K-ras or p53 mutation was detected in the serum in 40% of the 25 patients (95% confidence interval, 21-61%), whose primary tumors contained a mutation and in 23% of the 44 patients (95% confidence interval, 12-38%) with colorectal cancer. The frequent detection of p53 mutation in the serum of patients with early stage tumors suggests a possible use of this approach for clinical prognosis and cancer monitoring of colorectal cancer patients.

S-Adenosylmethionine-dependent reduction of lysine 2,3-aminomutase and observation of the catalytically functional iron-sulfur centers by electron paramagnetic resonance

Lysine 2,3-aminomutase catalyzes the interconversion of l-alpha-lysine and l-beta-lysine. The enzyme contains an iron-sulfur cluster with unusual properties, and it requires pyridoxal-5'-phosphate (PLP) and S-adenosylmethionine (AdoMet) for activity. The reaction proceeds by a substrate radical rearrangement mechanism, in which the external aldimine formed between PLP and lysine is initially converted into a lysyl-radical intermediate by hydrogen abstraction from C3. The present research concerns the mechanism by which a hydrogen-abstracting species is generated at the active site of lysine 2,3-aminomutase. Earlier tritium tracer experiments have implicated the 5'-deoxyadenosyl moiety of AdoMet in this process. AdoMet is here shown to interact with the iron-sulfur cluster at the active site of Clostridial lysine 2,3-aminomutase. Reduction of the iron-sulfur cluster from its EPR-silent form [4Fe-4S]2+ to the fully reduced form [4Fe-4S]1+ requires the presence of either AdoMet or S-adenosylhomocysteine (SAH) and a strong reducing agent such as dithionite or deazariboflavin and light. The reduced forms are provisionally designated E-[4Fe-4S]1+/AdoMet and E-[4Fe-4S]1+/SAH, and they display similar low-temperature EPR spectra centered at gav = 1.91. The reduced form E-[4Fe-4S]1+/AdoMet is fully active in the absence of any added reducing agent, whereas the form E-[4Fe-4S]1+/SAH is not active. It is postulated that the active form E-[4Fe-4S]1+/AdoMet is in equilibrium with a low concentration of a radical-initiating form that contains the 5'-deoxyadenosyl radical. Initiation of the radical rearrangement mechanism is postulated to take place by action of the 5'-deoxyadenosyl radical in abstracting a hydrogen atom from carbon-3 of lysine, which is bound as its external aldiminine with PLP. This process accounts for the results of tritium tracer experiments, it explains the radical rearrangement mechanism, and it rationalizes the roles of AdoMet and the [4Fe-4S] cluster in the reaction.

Screening for problem drinking and counseling by the primary care physician-nurse team

Present methods to screen for alcohol abuse are generally obtrusive and result in referral to services that deal mainly with alcoholics. These factors deter physicians from identifying alcohol abuse patients at an early stage. In the present study, 81% of all primary care physicians of a single city evaluated (i) the efficiency and the acceptability of a nonobtrusive screening method for the identification of problem drinkers and (ii) the effectiveness of brief cognitive behavioral counseling given by a nurse in a lifestyle context. Patients (n = 15,686) attending the private practices of 42 primary-care physicians were asked four alcohol-neutral trauma questions in the reception area. Physicians asked about alcohol use and alcohol-related problems only to patients with previous trauma. Problem drinkers by defined criteria were offered an appointment with a nurse who, by random assignment, gave either 3-hr of cognitive behavioral counseling over 1 year or simply advised patients to reduce their alcohol intake. The screening method identified 62-85% of expected number of problem drinkers in this population. Following the application of exclusion criteria, 105 problem drinkers were entered in the intervention part of the study. After 1 year, patients who received counseling showed significant reductions in reported alcohol consumption (-70%; p < 0.001), psychosocial problems (-85%; p < 0.001) and serum gamma glutamyl transferase (-32% to -58%; p < 0.02). Physician visits were reduced (-34%; p < 0.02) following counseling. Patients receiving only advice showed neither reductions in psychosocial problems nor in serum gamma glutamyl transferase or physician visits, but reported a 46% reduction (p < 0.01) in alcohol consumption. Data indicate that asking patients about recent trauma is efficient and is well accepted as the first screening instrument in the identification of the problem drinker. Cost of screening per patient is under one dollar. Counseling of 3 hr given by a nurse is markedly superior (p < 0.05) to simple advice in reducing alcohol consumption, objective indicators of alcohol-related morbidity, and the frequency of physician visits.

Expression in yeast and purification of functional macrophage nitric oxide synthase. Evidence for cysteine-194 as iron proximal ligand

Mouse macrophage NO-synthase (mNOS) was expressed in a unique yeast-based system by using a three-step procedure which allows yeast growth and NOS expression to be uncoupled. Despite cytotoxic effects related to mNOS expression, levels of catalytically active enzyme up to 0.5 mg of protein per 5 L of culture was obtained after purification. Its electrophoretic, spectroscopic [lambda max = 446 nm for its Fe(II)-CO complex], and catalytic properties were similar to those previously reported for mNOS purified from macrophages. Recombinant mNOS catalyzed the NADPH-dependent oxidation of L-arginine to citrulline (Km = 7 +/- 3 microM) as well as the reduction of cytochrome C by NADPH [Km = 34 +/- 8 microM and Vm = 25 +/- 5 mumol min-1 (mg of protein-1)]. Two mutants of mNOS in which Cys 194 was replaced with either serine or histidine were constructed and expressed in the same yeast strain at a level higher than that of the wild type protein, as they appear less toxic for the host. Both mutants exhibited electrophoretic properties and activities toward cytochrome C reduction identical to those of wild type NOS. However, they were unable to catalyze the oxidation of L-arginine to citrulline and did not appear to bind heme (no appearance of peaks around 400 and 446 nm for the resting enzyme and its CO complex, respectively, in visible spectroscopy). These data provide the first experimental evidence in favor of previous suggestions that Cys 194 was the proximal iron ligand of mouse mNOS.

Coenzyme B12-dependent ribonucleotide reductase: evidence for the participation of five cysteine residues in ribonucleotide reduction

Ribonucleoside triphosphate reductase (RTPR) from Lactobacillus leichmannii catalyzes the conversion of ribonucleotides to 2'-deoxyribonucleotides and requires adenosylcobalamin (AdoCbl) as a cofactor. Recent cloning, sequencing, and expression of this protein [Booker, S., & Stubbe, J. (1993) Proc. Natl. Acad. Sci. U.S.A. 90, 8352-8356] have now allowed its characterization by site-directed mutagenesis. The present study focuses on the role of five cysteines postulated to be required for catalysis. The choice of which of the ten cysteines of RTPR were to be mutated was based on extensive studies on the Escherichia coli ribonucleoside diphosphate reductase. Despite the differences between these two reductases in primary sequence, quaternary structure, and cofactor requirements, their mechanisms are strikingly similar. The mutagenesis studies reported herein further suggest that the complex role of the five cysteines is also very similar. A variety of single and double mutants of RTPR were prepared (C731S, C736S, C731 and 736S, C119S, C419S, C408S, and C305S), and their interaction with the normal substrate (CTP) was characterized under several sets of conditions. Mutants C731S, C736S, and C731 and 736S all catalyzed the formation of dCTP at rates similar to those of the wild-type (wt) enzyme in the presence of the artificial reductant DTT. In the presence of the in vivo reducing system (thioredoxin, thioredoxin reductase, and NADPH), however, each of these mutants catalyzed the formation of only 0.6-0.8 dCTPs per mole of enzyme. The inability of these mutants to catalyze multiple turnovers with respect to the in vivo reducing system suggests that their function might be to transfer reducing equivalents from thioredoxin into the active site disulfide of the reductase. Mutants C119S and C419S were targeted as being the active site cysteines, the ones which directly reduce the ribonucleotide substrate. As expected, neither of these mutants catalyzed the formation of dCTP. However, they did catalyze a time-dependent formation of cytosine, destruction of the cofactor, and the appearance of a chromophore associated with the protein--all phenotypes previously observed for the corresponding active site cysteines of the E. coli reductase. Mutant C408S was unable to catalyze dNTP production or cytosine release. Moreover, it was ineffective in catalyzing two additional reactions which are unique to this enzyme: the exchange of tritium from the 5' hydrogens of AdoCbl with H2O and the destruction of AdoCbl under anaerobic conditions to give 5'-deoxyadenosine and cob(II)alamin. These results are consistent with the role of this cysteine as the protein radical responsible for initiating catalysis.

Molecular diagnosis of familial adenomatous polyposis

BACKGROUND

Familial adenomatous polyposis is an inherited disease characterized by multiple colorectal tumors. The diagnosis has classically been based on the detection of multiple colorectal adenomas. The recent identification of germline mutations of the APC gene in patients with familial adenomatous polyposis makes presymptomatic molecular diagnosis possible, but the widespread distribution of the many mutations within this very large gene have heretofore made the search for such mutations impractical. We describe a novel approach that allows molecular genetic diagnosis in the majority of patients with the disease.

METHODS

We screened 62 unrelated patients from the Johns Hopkins Familial Adenomatous Polyposis Registry for germline APC mutations. Primary screening was accomplished by analysis of protein synthesized in vitro from surrogate APC genes. In addition, the relative amount of transcript from each APC allele was determined with an allele-specific--expression assay.

RESULTS

The protein assay revealed truncated protein in 51 of the 62 patients (82 percent). In 3 of the 11 remaining patients, the allele-specific--expression assay revealed significantly reduced expression of one allele of the APC gene. The use of these two assays in combination successfully identified germline APC mutations in 87 percent of the 62 patients.

CONCLUSIONS

The protein and allele-specific--expression assays provide a practical and sensitive method for molecular diagnosis of familial adenomatous polyposis. This approach will facilitate care, allowing routine testing of subjects at risk and genetic confirmation of spontaneous mutations.

Cloning, sequencing, and expression of the adenosylcobalamin-dependent ribonucleotide reductase from Lactobacillus leichmannii

Ribonucleoside-triphosphate reductase (RTPR, EC 1.17.4.2) from Lactobacillus leichmannii, a monomeric adenosylcobalamin-requiring enzyme, catalyzes the conversion of nucleoside triphosphates to deoxynucleoside triphosphates. The gene for this enzyme has been cloned and sequenced. In contrast to expectations based on mechanistic considerations, there is no statistically significant sequence homology with the Escherichia coli reductase that requires a dinuclear-iron center and tyrosyl radical cofactor. The RTPR has been overexpressed and purified to homogeneity, yielding 90 mg of protein from 2.5 g of bacteria. Initial characterization of the recombinant RTPR indicates that its properties are identical to those of the RTPR isolated from L. leichmannii.

Ribonucleotide reductases: radical enzymes with suicidal tendencies

Ribonucleotide reductases isolated from E. coli and from L. leichmannii differ considerably in their primary and quaternary structures, as well as in their cofactor requirements. Despite these differences, studies with the wt enzymes and the normal substrate, and with the wt enzymes and a variety of mechanism-based inhibitors, demonstrate amazing mechanistic similarities between the two reductases. Recent studies with five cysteine mutants of both reductases reveal strikingly similar phenotypes, indicating that, despite the differences in the primary structures, the groups involved in catalysis in both enzymes appear to be similar.

A model for the role of multiple cysteine residues involved in ribonucleotide reduction: amazing and still confusing

Ribonucleotide reductase from Escherichia coli catalyzes the conversion of nucleotides to deoxynucleotides. Multiple cysteins have been postulated to play a key role in this process. To test the role of various cysteines in nucleotide reduction, a variety of single and double mutants of the R1 subunit were prepared: C754S, C759S, C754-759S, C462S, C462A, C230S, and C292S. Due to the expression system, each mutant contains small amounts of contaminating wt-R1 (estimated to be 1.5-3% based on activity). An epitope tagging method in conjunction with anion exchange chromatography was used to partially resolve the mutant R1 from the wt-R1. The interaction of these mutants with the normal substrate was studied, which allowed a model to be proposed in which five cysteines of the R1 subunit of RDPR play a role in catalysis. C754S and C759S R1s catalyze CDP formation at rates similar to wt-R1 when DTT is used as a reductant. However, when thioredoxin (TR)/thioredoxin reductase (TRR)/NADPH is used as reductant, the rates of dNDP production are similar to those expected for contaminating wt-R1 present as a heterodimer with the mutant. The impaired nature of these mutants with respect to reduction by TR suggests that their function is to transfer reducing equivalents from TR to the active site disulfide of R1 produced during NDP reduction. Single-turnover experiments, designed to avoid the problem of contaminating wt-R1, also support this role for C754 and C759. The double serine mutant of 754 and 759 has catalytic activity with DTT that is one-third the rate of wt-R1 with thioredoxin. C225 and C462 are thought to be the active site cysteines oxidized concomitantly with NDP reduction. Conversion of these cysteines to serines results in R1 mutants which convert the normal substrate into a mechanism-based inhibitor. C462SR1 upon incubation with R2 and [3'-3H,U-14C]UDP results in uracil release, 3H2O production, 3H,14C-labeled protein which has an absorbance change at 320 nm, and slow loss of the tyrosyl radical on R2. The isotope effect (kH/k3H) on 3' carbon-hydrogen bond cleavage is 1.7. This sequence of events is independent of the reductant, consistent with the postulate that C462 is an active site thiol. The C462AR1 has properties similar to C462SR1. Several additional mutant R1s, C230SR1, and C292SR1 were shown to have activities similar to wt-R1 with both TR/TRR/NADPH and DTT.