The essential role of population health during and beyond COVID-19

The coronavirus disease 2019 (COVID-19) pandemic has fundamentally changed how health care systems deliver services and revealed the tenuousness of care delivery based on face-to-face office visits and fee-for-service reimbursement models. Robust population health management, fostered by value-based contract participation, integrates analytics and agile clinical programs and is adaptable to optimize outcomes and reduce risk during population-level crises. In this article, we describe how mature population health programs in a learning health system have been rapidly leveraged to address the challenges of the pandemic. Population-level data and care management have facilitated identification of demographic-based disparities and community outreach. Telemedicine and integrated behavioral health have ensured critical primary care and specialty access, and mobile health and postacute interventions have shifted site of care and optimized hospital utilization. Beyond the pandemic, population health can lead as a cornerstone of a resilient health system, better prepared to improve public health and mitigate risk in a value-based paradigm.

Patient primary language in a culturally focused intervention for Latino Americans with depression

BACKGROUND

This study examined whether a culturally focused psychiatric consultation program (CFP) for Latino Americans was equally effective in reducing depressive symptoms in English-speaking and Spanish-speaking patients.

METHODS

The CFP utilizes the Engagement Interview Protocol (EIP), a semi-standardized protocol eliciting patient narratives about illness beliefs. The sample included 118 Latino American patients presenting with depressive symptoms. Patient-preferred primary language was examined as a moderator for the effect of CFP participation vs usual care on change in depressive symptoms.

RESULTS

Multiple regression analysis revealed that the interaction effect of primary language and treatment arm on depressive symptoms, as measured by the Quick Inventory of Depressive Symptomatology-Self Report was not statistically significant at 6-month follow-up (B = -2.89, t = -1.35, P = .180).

CONCLUSIONS

The findings suggest that the CFP was equally effective in both Spanish and English-speaking Latino Americans. The trend in the results toward greater reduction in depressive symptoms in primary Spanish-speaking Latino Americans as compared with primary English-speaking Latino Americans suggests the importance of receiving language-concordant care.

Association of Race, Ethnicity and Language with Participation in Mental Health Research Among Adult Patients in Primary Care

Racial and ethnic minorities remain underrepresented in clinical psychiatric research, but the reasons are not fully understood and may vary widely between minority groups. We used the Z-test of independent proportions and binary logistic regression to examine the relationship between race, ethnicity or primary language and participation in screening as well as interest in further research participation among primary care patients being screened for a depression study. Minorities were less likely than non-Hispanic Whites to complete the initial screening survey. Latinos and Blacks were more likely to agree to be contacted for research than non-Hispanic Whites. Among Latinos, primary language was associated with willingness to be contacted for research. Associations between research participation and race, ethnicity and language are complex and vary across different enrollment steps. Future research should consider stages of the research enrollment process separately to better understand barriers and identify targets for intervention.

Association Between Stigma and Depression Outcomes Among Chinese Immigrants in a Primary Care Setting

OBJECTIVE

Stigma has been proposed to be a major underlying factor contributing to lower rates of mental health service utilization among racial/ethnic minorities in the United States. Yet, surprisingly little research has specifically explored associations between stigma, race/ethnicity, and psychiatric morbidity. This study aims to assess the impact of stigmatizing attitudes on depression outcomes among a psychiatrically underserved, immigrant Chinese population.

METHODS

Between 2009 and 2012, 190 Chinese immigrants with major depressive disorder as diagnosed by the Mini International Neuropsychiatric Interview were enrolled in a trial of culturally sensitive collaborative care for depression. Participants' self-reported stigma regarding their symptoms was assessed at study entry using the Explanatory Model Interview Catalogue, and depressive symptoms were assessed with the Hamilton Depression Rating Scale (HDRS) at baseline and follow-up. Hierarchical linear regression was used to assess the association between baseline stigma score and change in HDRS score, adjusting for potential confounders.

RESULTS

Higher stigma scores at baseline were significantly associated with attenuated improvement in both HDRS score and quality of life at 6 months (P < .05 for both).

CONCLUSIONS

Stigma has a directly harmful effect on depression outcomes, even after individuals have been accurately diagnosed within a culturally sensitive community health center and agreed to treatment. These results support further research into interventions targeting stigma to improve mental health outcomes among minority populations.

TRIAL REGISTRATION

This study is a secondary analysis of prospectively collected data from the randomized controlled trial registered by ClinicalTrials.gov identifier: NCT00854542.

The Effectiveness of Telepsychiatry-Based Culturally Sensitive Collaborative Treatment for Depressed Chinese American Immigrants: A Randomized Controlled Trial

OBJECTIVE

This study evaluates the effectiveness of a telepsychiatry-based culturally sensitive collaborative treatment (T-CSCT) intervention to improve treatment outcomes for depressed Chinese American immigrants.

METHODS

Participants were Chinese Americans recruited from primary care settings from February 1, 2009, to July 31, 2012, with DSM-IV major depressive disorder (MDD) identified by the Mini-International Neuropsychiatric Interview. Eligible patients were randomized to receive either T-CSCT or treatment as usual (TAU) for 6 months. T-CSCT involves (1) cultural consultation via videoconference and (2) care management. The primary outcome measure was the 17-item Hamilton Depression Rating Scale (HDRS₁₇); positive response was defined as a ≥ 50% decrease in HDRS₁₇ score, and remission was defined as HDRS₁₇ score ≤ 7. Secondary outcome measures were the Clinical Global Impressions-Severity of Illness (CGI-S) and Improvement (CGI-I) scales and the Quality of Life Enjoyment and Satisfaction Questionnaire (Q-LES-Q). Outcomes were compared using multivariate logistic regression and mixed-model for repeated measures methods.

RESULTS

Among participants (N = 190), 63% were female, and the mean (SD) age was 50 (14.5) years. They were randomized to T-CSCT (n = 97; 51%) or TAU (n = 93; 49%). Using multivariate logistic regression analyses, the odds of achieving response and remission were significantly greater for the T-CSCT group compared to the control group (odds ratio [OR] = 3.9 [95% CI, 1.9 to 7.8] and 4.4 [95% CI, 1.9 to 9.9], respectively). Multivariate general linear model analyses showed that patients in the T-CSCT group had significantly greater improvement over time in HDRS₁₇ (F4,95 = 4.59, P = .002), CGI-S (F4,95 = 4.22, P = .003), and CGI-I (F4,95 = 2.95, P = .02) scores.

CONCLUSIONS

T-CSCT is effective in improving treatment outcomes of Chinese immigrants with MDD.

TRIAL REGISTRATION

ClincialTrials.gov identifier: NCT00854542.

Race/ethnicity and other social determinants of psychological well-being and functioning in mental health clinics

Significant racial and ethnic differences exist in the receipt of psychiatric care and help-seeking. We examined the relationship between race/ethnicity and psychological well-being and functioning in psychiatric outpatients. We analyzed intake data for 8,697 adult patients in psychiatry clinics in New England between 2008 and 2010. Patients rated psychological wellbeing using the Schwartz Outcome Scale (SOS-10); clinicians rated the Global Assessment of Functioning (GAF). In an analysis of variance with covariates, race/ethnicity exhibited a small but statistically significant association with GAF (F(4,8481)=17.902, p&lt;.001) and SOS-10 scores (F(4,8165)=7.271, p&lt;.001). However, after adjustment for physical health and socioeconomic variables, these differences became insignificant or were reversed. Our findings suggest that the relationship between race/ethnicity and mental health may be confounded by other socioeconomic or health differences and may be small compared with the effect of those variables. Future studies on race and psychological well-being should take social determinants of health into consideration.

Use of the Patient Health Questionnaire-9 and a detailed suicide evaluation in determining imminent suicidality in distressed patients with cardiac disease

BACKGROUND

The risk of suicide is elevated in patients with cardiac disease in comparison with the general population.

OBJECTIVE

In distressed cardiac inpatients, we explored the use of Item 9 of the Patient Health Questionnaire-9, which inquires about thoughts of death or suicide, and a detailed suicide evaluation (DSE) triggered by positive responses to Item 9 as means of assessing suicide.

METHODS

Among cardiac inpatients endorsing current emotional distress, we recorded the prevalence of positive responses to Item 9, gathered information about outcomes and time spent completing the DSE, and examined the frequency of imminent suicidality identified by the DSE among Item 9-positive patients.

RESULTS

Among 366 patients, 77 (21%) answered affirmatively to Item 9. All DSEs were successfully completed but consumed 17 clinician hours. Among the 71 patients receiving the DSE, 2 (0.5% of total sample; 2.8% of Item 9-positive patients) were imminently suicidal (i.e., had intent or plan).

CONCLUSION

Nearly 1 in 4 patients had a positive response to Item 9, but very few had imminent suicidality; the DSE was easy to use and acceptable to patients but time consuming. A more narrowly focused alternative to Item 9 may more accurately predict imminent suicidality and reduce the burden of further detailed suicide screening.

Impact of a culturally focused psychiatric consultation on depressive symptoms among Latinos in primary care

OBJECTIVE

A culturally focused psychiatric (CFP) consultation service was implemented to increase engagement in mental health care and reduce depressive symptoms among adult Latino primary care patients. The aim of this study was to assess preliminary efficacy of the CFP consultation service to reduce depressive symptoms.

METHODS

In a randomized controlled study, primary care clinics were randomly selected to provide either the two-session CFP intervention or enhanced usual care. For CFP intervention participants, study clinicians (psychologists or psychiatrists) provided a psychiatric assessment, psychoeducation, cognitive-behavioral tools, and tailored treatment recommendations; primary care providers were provided a consultation summary. Depressive symptoms (as measured by the Quick Inventory of Depressive Symptomatology-Self Rated [QIDS-SR]) were assessed at baseline and six-month follow-up. Multiple regression analysis was conducted to evaluate whether CFP intervention participants showed greater improvement in depressive symptoms at follow-up, with control for baseline depression, clinic site, and significant covariates.

RESULTS

Participants (N=118) were primarily Spanish-monolingual speakers (64%). Although depressive symptoms remained in the moderate range for both groups from baseline to six months, symptom reduction was greater among CFP intervention participants (mean±SD change in QIDS-SR score=3.46±5.48) than those in usual care (change=.09±4.43). The final multiple regression model indicated that participation in the CFP intervention predicted lower depressive symptoms at follow-up (unstandardized beta=-3.09, p=.008), independent of baseline depressive symptoms, clinic site, age, gender, and employment status.

CONCLUSIONS

Results suggest that Latinos experiencing depressive symptoms may benefit from a short-term CFP consultation. Findings also support the integration of psychiatric interventions for Latinos in the primary care setting.

Depression monitoring and patient behavior in the Clinical Outcomes in MEasurement-Based Treatment (COMET) trial

OBJECTIVE

In this secondary analysis of results of the Clinical Outcomes in MEasurement-Based Treatment (COMET) trial, patient behaviors that might account for the differences observed in clinical outcomes were examined.

METHODS

Patients (N=914) diagnosed as having major depressive disorder participated in telephone interviews either monthly for six months (intervention) or at three and six months (usual care) asking about antidepressant medication-taking, use of psychotherapy or counseling, and participation in depression support groups. Physicians (N=83) in the intervention arm received monthly feedback regarding their patients' depression severity.

RESULTS

A total of 664 (73%) patients completed the month 6 interview. The adjusted odds of current antidepressant use at six months were 85% greater (p=.01) for patients in the intervention (N=380) versus usual care (N=284) arms, according to multivariate regression analyses.

CONCLUSIONS

More frequent measurement of depression symptoms was associated with greater medication persistence, which in turn may have mediated clinical improvements.

Clinical Outcomes in Measurement-based Treatment (Comet): a trial of depression monitoring and feedback to primary care physicians

BACKGROUND

Despite the availability of effective treatments for depression, many patients under the care of primary care physicians do not achieve remission. Clinical Outcomes in Measurement-based Treatment (COMET) was designed to assess whether communicating patient-reported depression symptom severity to primary care physicians affects patient outcomes at 6 months.

METHODS

Nine hundred fifteen patients (intervention: n = 503; control: n = 412) diagnosed with major depressive disorder were enrolled in a prospective trial in which physician practice sites were assigned to either the intervention or control study arm. Only patients who were prescribed an antidepressant by their physician were eligible, but medication type was independent of the study protocol. Intervention-arm physicians received monthly updates on their patients' depression severity, which was determined with the nine-item Patient Health Questionnaire (PHQ-9) administered during telephone interviews. Remission was defined as a PHQ-9 score <5 at 6 months; response was defined as a score reduction ≥50%.

RESULTS

Among patients with baseline PHQ-9 score ≥5, 45.0% achieved remission (46.7% intervention versus 42.8% control) and 63.9% responded (67.0% intervention versus 59.7% control) at 6 months. After adjusting for baseline demographic and clinical variables, odds of remission (odds ratio [OR], 1.59 [95% CI, 1.07-2.37]) or response (OR, 2.02 [95% CI, 1.36-3.02]) were significantly greater for the intervention group than for control patients.

CONCLUSIONS

This study demonstrated that regular patient symptom monitoring with feedback to physicians improved outcomes of depression treatment in the primary care setting. Determining reasons for the high observed nonremission rates requires further investigation.

Effect of communicating depression severity on physician prescribing patterns: findings from the Clinical Outcomes in MEasurement-based Treatment (COMET) trial

OBJECTIVE

In this secondary analysis from the Clinical Outcomes in MEasurement-based Treatment trial (COMET), we evaluated whether providing primary care physicians with patient-reported feedback regarding depression severity affected pharmacological treatment patterns.

METHOD

Intervention-arm physicians received their patients' 9-item Patient Health Questionnaire scores monthly. Odds of having no change in antidepressant treatment during the 6-month study period were calculated. Relationships between depression symptom status (partial or nonresponse) at month 3 and treatment changes in months 3 through 6 were assessed.

RESULTS

Among 503 intervention and 412 usual care (UC) patients with major depressive disorder, most received antidepressant monotherapy at baseline (79.4% UC vs. 88.4% intervention; P=.047). Few switched their baseline antidepressant (17.4%), increased their dose (12.4%) or augmented with a second medication (2%). Odds of having no change in antidepressant therapy did not differ significantly between study arms (odds ratio 1.21; 95% confidence interval 0.78-1.88; P=.392). Few month 3 partial or nonresponders had a regimen change over the following 3 months; the study arms did not differ significantly (partial responders: 4.1% UC vs. 7.7% intervention; P=.429; nonresponders: 14.6% UC vs. 15.9% intervention; P=.888).

CONCLUSIONS

Among depressed patients treated in primary care, little active management was observed. The lack of treatment modification for the majority of partial and nonresponders was notable.

Using the Electronic Medical Record to Examine Racial and Ethnic Differences in Depression Diagnosis and Treatment in a Primary Care Population

OBJECTIVE

We assessed racial and ethnic differences in depression diagnosis and treatment in a primary care population.

METHODS

A sample of primary care outpatients in 2007 was generated using the electronic medical record (EMR). Patients were considered depressed if their providers billed for depression-related codes; they were considered prescribed antidepressants if any antidepressants were on their medication list. Rates of diagnosis and medication prescription were estimated using a generalized linear model with a Poisson distribution, adjusting for covariates.

RESULTS

In the resulting sample (n=85,790), all minority groups were less likely to be diagnosed with depression as compared to Whites (p<0.05); 11.36% of Whites had a depression diagnosis, as compared to 6.44% of Asian Americans, 7.55% of African Americans, and 10.18% of Latino Americans. Among those with a depression diagnosis (n=11,096), 54.07% of African Americans were prescribed antidepressant medications, as compared to 63.19% Whites (p<0.05); Asian Americans and Latino Americans showed a trend of being less likely to be prescribed antidepressant medications.

CONCLUSIONS

Our study illustrates differences in diagnosis and treatment for minority primary care patients, and is innovative in using the EMR to probe these differences. Further research is needed to understand the underlying reasons for these observed differences.

The Engagement Interview Protocol (EIP): improving the acceptance of mental health treatment among Chinese immigrants

Many depressed Chinese immigrants are unfamiliar with Western psychiatric terminology and have high levels of stigma toward psychiatric illnesses, making it difficult to engage them into psychiatric treatment. We have designed the Engagement Interview Protocol (EIP), a semi-standardized protocol that incorporates cultural components to a standard psychiatric evaluation. The EIP elicits patients' narratives and uses anthropological questions to explore patients' illness beliefs, which are integrated with patients' information on medical and psychiatric history, psychosocial background and mental status examination so that treatment options can be negotiated in a culturally sensitive manner. In our field testing on depressed Chinese immigrants, the EIP model was found to be a practical tool that can be completed within the allotted one-hour time frame and was highly effective in facilitating the enrollment of patients in treatment for depression. The EIP is a concise, time-effective, user-friendly protocol that can be used both in research and real-world clinical settings with diverse patient populations.

A study of a culturally focused psychiatric consultation service for Asian American and Latino American primary care patients with depression

BACKGROUND

Ethnic minorities with depression are more likely to seek mental health care through primary care providers (PCPs) than mental health specialists. However, both provider and patient-specific challenges exist. PCP-specific challenges include unfamiliarity with depressive symptom profiles in diverse patient populations, limited time to address mental health, and limited referral options for mental health care. Patient-specific challenges include stigma around mental health issues and reluctance to seek mental health treatment. To address these issues, we implemented a multi-component intervention for Asian American and Latino American primary care patients with depression at Massachusetts General Hospital (MGH).

METHODS/DESIGN

We propose a randomized controlled trial to evaluate a culturally appropriate intervention to improve the diagnosis and treatment of depression in our target population. Our goals are to facilitate a) primary care providers' ability to provide appropriate, culturally informed care of depression, and b) patients' knowledge of and resources for receiving treatment for depression. Our two-year long intervention targets Asian American and Latino American adult (18 years of age or older) primary care patients at MGH screening positive for symptoms of depression. All eligible patients in the intervention arm of the study who screen positive will be offered a culturally focused psychiatric (CFP) consultation. Patients will meet with a study clinician and receive toolkits that include psychoeducational booklets, worksheets and community resources. Within two weeks of the initial consultation, patients will attend a follow-up visit with the CFP clinicians. Primary outcomes will determine the feasibility and cost associated with implementation of the service, and evaluate patient and provider satisfaction with the CFP service. Exploratory aims will describe the study population at screening, recruitment, and enrollment and identify which variables influenced patient participation in the program.

DISCUSSION

The study involves an innovative yet practical intervention that builds on existing resources and strives to improve quality of care for depression for minorities. Additionally, it complements the current movement in psychiatry to enhance the treatment of depression in primary care settings. If found beneficial, the intervention will serve as a model for care of Asian American and Latino American patients.

Antipsychotic polytherapy on an inpatient psychiatric unit: how does clinical practice coincide with Joint Commission guidelines?

OBJECTIVE

A recently developed quality measure set for inpatient psychiatric care includes measurement of antipsychotic polytherapy at discharge. Our objective was to use detailed chart reviews to assess the use of antipsychotic polytherapy and place this use in the context of these measures.

METHODS

Patients (N=75) discharged on multiple antipsychotics and a comparable set (N=114) of comparison patients (a randomly selected set of all admitted inpatients) were identified from consecutive admissions to a psychiatric inpatient unit. Medical records were reviewed to ascertain the clinical rationale for antipsychotic polytherapy and assess differences in characteristics between these groups.

RESULTS

Patients discharged on antipsychotic polytherapy were more likely to have public insurance, longer lengths of stay, psychotic illness, more prior admissions, and state-funded services for persons with chronic mental illness. We identified subgroups of patients based on the clinical rationale for the antipsychotic co-prescription (refractory illness, regimen unchanged from admission and use of antipsychotic for nonpsychosis symptoms). Some, but not all, such rationales appeared to be clinically justified.

CONCLUSIONS

The majority of patients discharged on antipsychotic polytherapy had justifiable clinical rationales that were concordant with the new quality measures. However, two additional subsets were identified, one where quality improvement efforts may be warranted and another where revision of existing quality measure definitions should be considered. Given the implications of public reporting of quality measures, further study and refinement of these measures are required to provide meaningful information to all concerned stakeholders.

Using electronic medical records to determine the diagnosis of clinical depression

OBJECTIVE

To investigate the validity of using electronic medical records (EMR) database in a large health organization for identifying patients with clinical depression.

METHOD

The Massachusetts General Hospital EMR system was used to generate a sample of primary care patients seen in the primary care clinic in 2007. Using this sample, the validity of using certain fields in the EMR database (i.e., billing diagnosis, problem list, and medication list) to identify patients with clinical depression was compared to primary care physician (PCP) assessment by a written questionnaire. Based on this standard, the sensitivity, specificity, positive predictive value, negative predictive value, and the areas under receiver operating characteristic curve (AUC) of three specific EMR fields - individually and in combination - were calculated to identify which EMR field best predicted PCP classification.

RESULTS

The EMR fields "billing diagnosis", "problem list" and antidepressant in "medication list", were all able to identify patients' diagnosis of depression by their PCPs reasonably well. Having one or more "billing diagnosis" of depression had the highest sensitivity and highest AUC (77% sensitivity, 76% specificity, AUC 0.77) among any of the fields used alone.

CONCLUSION

The AUC for "billing diagnosis" of depression performed the best of the three single fields tested, with an AUC of 0.77, corresponding to a test with moderate accuracy. This analysis demonstrates that specific EMR fields can be used as a proxy for PCP assessment of depression for this EMR system. Limitations to our analysis include the physician response rate to our survey as well as the quality of the data, which is collected primarily for administrative and clinical purposes. When using administrative and clinical data in mental health studies, researchers must first assess the accuracy of choosing specific fields within their EMR system in order to determine the level of accuracy for them to be used as proxies for clinical diagnoses.

Circulating hepatitis B virus nucleic acids in chronic infection : representation of differently polyadenylated viral transcripts during progression to nonreplicative stages

PURPOSE

Beside the established maturation of hepatitis B virus (HBV) transcripts at a polyadenylation signal downstream of the HBV x protein open reading frame, maturation at an internal polyadenylation signal has been observed in the chronically infected liver. In the present study, it was the aim to identify the respective circulating full-length and truncated transcripts in plasma/serum of carriers.

EXPERIMENTAL DESIGN

Nucleic acids extracted from sera were analyzed using established PCR and reverse transcription-PCR procedures targeted to HBV x protein gene regions. Amplification products were cloned and sequenced.

RESULTS

Base substitution patterns were determined, which indicated infection stages advanced to different degrees regardless of the transcript type analyzed. HBV full-length RNA (fRNA) showed a high correlation with hepatitis B e antigen and viral DNA, indicative for a replicative infection. In contrast, truncated RNA (trRNA) appeared to be independent of hepatitis B e antigen and showed only a weak association with circulating viral DNA. No correlation was observed between the levels of trRNA and the apparent liver damage as reflected by alanine transaminase levels. An age-dependent representation of fRNA and trRNA was observed: fRNA decreased progressively to low levels, whereas trRNA remained at comparably high values. trRNA and RNA not polyadenylated at either of the two polyadenylation signals were detected even in the absence of any other conventional HBV seromarker, including viral DNA. This was shown for patients with cryptogenic cirrhosis and hepatitis C virus carriers.

CONCLUSIONS

The identification of HBV RNA in human serum has a diagnostic potential for apparent and for inapparent infection stages.

[Simple testicular cyst]

High-resolution sonograms of scrotum in two hundred and ninety six patients were reviewed. Twenty six patients were found to have simple testicular cyst(s). The specific features of cyst, which included sharp clear margin, anechoic content, posterior wall enhancement and no adjacent echogenic mass, could be found in all lesions. Four cases had bilateral testicular involvement. Solitary cystic lesion was found in 14 tests. The size ranged from 2.0 mm to 1.2 cm. Clustered cystic lesions were found in six testes. The size ranged from 4.0 mm to 2.5 cm. More than one focal lesion were found in 10 testes. Twenty four of these thirty testes had tunica albuginea cyst(s) or cyst(s) abutting on testicular margins. Four patients had follow-up sonograms with the period ranging from three months to two years. No remarkable change of all lesions were noted. The sonographic pictures and its patterns were presented. The pathogenesis and the literature were briefly reviewed.

Ultrasonographic demonstration of duplication cyst of the ileum

The enteric duplication cyst is a term applied to an anomaly of the gut which presents as a cystic structure with a mucosal lining predominantly similar to that of the adjacent alimentary tract. It may be either due to an embryologic error in normal canalization or errors in the embryologic connection between the developing gut and neural tube, as a part of the split notochord syndrome. The preoperative diagnosis of a duplication cyst is difficult to make on the basis of conventional radiologic study including barium swallowing gastrointestinal series. With the wide application of ultrasound in the detection and evaluation of pediatric abdominal masses, an intra-abdominal cystic lesion may be encountered and the differential diagnoses may be difficult or impossible. We hereby report a case of duplication cyst of the ileum in which we believe its sonographic appearance is of certain value or even diagnostic in this pathology.

Purification and Characterization of Glutamyl-tRNA Synthetase : An Enzyme Involved in Chlorophyll Biosynthesis

Chlorophyll biosynthesis starts with the synthesis of glutamyl-tRNA (glu-tRNA) by a glutamyl-tRNA synthetase (Glu RS). The glu-tRNA is subsequently transformed to delta-aminolevulinic acid (ALA), which is a committed and regulated precursor in the chlorophyll biosynthetic pathway. The Glu RS from a green alga, Chlamydomonas reinhardtii, was purified and shown to be able to synthesize glu-tRNA and to participate in ALA synthesis in a coupled enzyme assay. Physical and chemical characterization of the purified Glu RS indicated that the enzyme had been purified to homogeneity. The purified enzyme has a native molecular weight of 60,000, an isoelectric point of 4.6, and it formed a single band of 32,500 daltons when analyzed by a silver stained denaturing gel. The N-terminal amino acid sequence of the 32,500 dalton protein was determined to be Asn-Lys-Val-Ala-Leu-Leu-Gly-Ala-Ala-Gly. The molecular weight analyses together with the unambiguous N-terminal amino acid sequence obtained from the purified enzyme suggested that the native enzyme was composed of two identical subunits. Polyclonal antibodies raised against the purified and denatured enzyme were able to inhibit the activity of the native enzyme and to interact specifically with the 32,500 dalton band on Western blots. Thus, the antibodies provided an additional linkage for the structural and functional identities of the enzyme. In vitro experiments showed that over 90% of the glu RS activity was inhibited by 5 micromolar heme, which suggested that Glu RS may be a regulated enzyme in the chlorophyll biosynthetic pathway.

Identification of an intermediate of delta-aminolevulinate biosynthesis in Chlamydomonas by high-performance liquid chromatography

The first committed intermediate of the chlorophyll biosynthetic pathway is delta-aminolevulinic acid (ALA). In plant cells, ALA is formed from glutamate by a pathway not yet clearly defined. One of the proposed pathways involves the reduction of glutamate to glutamate-1-semialdehyde (GSA) via a glutamyl-tRNA intermediate. GSA is then converted to ALA by an aminotransferase. We are studying this pathway using partially purified components from Chlamydomonas reinhardtii in in vitro reactions with [3H]L-glutamate as the substrate and analysis of the radioactive reaction products via HPLC. In reactions either lacking GSA-aminotransferase or containing gabaculine (an inhibitor of aminotransferase), a radioactive intermediate is formed which cochromatographs with synthetic GSA. As observed previously for ALA synthesis, the synthesis of this intermediate has an absolute requirement for RNA, ATP, and active enzymes, while the requirement for NADPH is less stringent. Both the accumulated intermediate and the synthetic GSA can be converted to ALA by the aminotransferase without any additional substrates or cofactors. These results support previous observations that GSA or a very similar compound is an intermediate of ALA synthesis.