Rapid determination of the relative configuration of diverse 8,4'-oxyneolignans by NMR analysis: Retrospective studies, improvement and structural revision

The characteristic 1H NMR signals (H-7 and H2-9) are significant parameters that have been widely used to assess the relative configuration of H-7 and H-8 of 8,4'-oxyneolignans. However, many usual 8,4'-oxyneolignans cannot be accurately determined by existing NMR methods and no research considering their limitations was performed until now. In this study, the application scope of NMR methods was comprehensively studied and the ΔδH9a-H9b methods have been extended to solve the majority of configuration determination difficulties. The accuracy of extended NMR methods was verified by anisotropic NMR (RCSA measurements), NMR calculation and diverse statistical analysis (MAEΔΔδ, CP3 and DP4+). Furthermore, the theoretical conformational analysis was performed to investigate the inherent limitations of existing NMR methods. This study could provide a valuable reference for determining the relative configuration of H-7 and H-8 in 8,4'-oxyneolignans and the relative configuration of 23 recently reported 8,4'-oxyneolignan derivatives should be reassigned as well.

Insight into tetrahydrofuran lignans from Isatis indigotica fortune with neuroprotective and acetylcholinesterase inhibitor activity

Nine tetrahydrofuran lignans, including three undescribed spiro-lignans, were isolated from Isatis indigotica Fortune (Brassicaceae). Extensive spectroscopic analyses achieved the structure elucidation of these tetrahydrofuran lignans, and quantum chemical calculation combined with the MAE_ΔΔδ parameter. Notably, isatispironeols A-B have a unique spiro[dienone-tetrahydrofuran] molecular core. These spiro[dienone-tetrahydrofuran] lignans showed comparable neuroprotective effects as the positive control in the H₂O₂-induced SH-SY5Y cells model. In addition, (-)-(7R,8S,1'R,7'R,8'R)-isatispironeol A possessed more significant AChE inhibitory activity, further interact sites were also predicted by the in silico assay.

The nature compound dehydrocrenatidine exerts potent antihepatocellular carcinoma by destroying mitochondrial complexes in vitro and in vivo

Cumulative evidence indicates that mitochondria dysfunction plays an important role in tumour treatment. Given the limited efficacy and toxicity of current mitochondria-targeted drugs, research into effective mitochondria-targeted anticancer agents remains an irresistible general trend. In this study, it was found that dehydrocrenatidine (DEC), a β-carbolin alkaloid isolated from Picrasma quassiodes, displays a promising growth inhibitory effect in vitro and in vivo by inducing apoptosis of hepatocellular carcinoma (HCC) cells. Mechanistically, we provided that the possible target of DEC against HCC cells was determined by isobaric labels for relative and absolute quantification assay and validated them using further experiments. The results suggested that DEC can target and regulate the function of mitochondrial complexes I, III and IV, affecting oxidative phosphorylation and ultimately leading to mitochondrial dysfunction to exert its anti-HCC effects. In addition, the combination of DEC and sorafenib showed a synergistic effect and was also associated with mitochondrial dysfunction. Importantly, DEC did not show significant toxicity in mice. This study provided a new insight into underlying mechanisms in DEC-treated HCC cells, suggesting that DEC might be a mitochondrial targeting lead compound.

Discovery of alkaloids from the leaves of Isatis indigotica Fortune with neuroprotective activity

Seven alkaloids including five undescribed ones (1a/1b, 2, 3 and 5) were obtained from the leaves of Isatis indigotica Fortune. Their structures were established by extensive spectroscopic analyses. The absolute configurations of compounds 1a, 1b, 3 and 5 were determined by comparison of the experimental and calculated electronic circular dichroism (ECD) spectra. Subsequently, the neuroprotective effects of all the isolates against H₂O₂-induced injury in SH-SY5Y cells were evaluated in vitro by MTT assay. Moreover, Annexin V-FITC/PI double staining was performed, while the activities of antioxidant enzymes (SOD, CAT and GSH-Px) for compounds 1a and 1b were measured.

[Association of age distribution with the expression of angiotensin-converting enzyme 2 in lung tissues in severe acute respiratory syndrome coronavirus 2 infection: reflections from the study of RAS pathway expression in mice]

OBJECTIVE

To study the expression of angiotensin-converting enzyme 2 (ACE2) and other key molecules of the RAS pathway in normal mice at different developmental stages, and to provide ideas for understanding the infection mechanism of coronavirus disease 2019 (COVID-19) as well as the diagnosis and treatment of children with COVID-19.

METHODS

The mice at different developmental stages were enrolled, including fetal mice (embryonic days 14.5 and 18.5), neonatal mice (0, 3, 7, 14, and 21 days old), young mice (28 and 42 days old), and adult mice (84 days old). The lung tissues of all fetal mice from 4 pregnant mice were collected at each time point in the fetal group. Four mice were sampled in other age groups at each time point. Whole transcriptome resequencing was used to measure the mRNA expression of AGT, ACE, ACE2, Renin, Agtr1a, Agtr1b, Agtr2, and Mas1 in mouse lung tissue.

RESULTS

The expression of ACE2 in the lungs showed changes from embryonic stage to adult stage. It increased gradually after birth, reached a peak on day 3 after birth, and reached a nadir on day 14 after birth (P<0.05). The expression of AGT reached a peak on days 0 and 7 after birth and reached a nadir on day 21 after birth (P<0.05). The expression of ACE increased rapidly after birth and reached a peak on day 21 after birth (P<0.05). Agtr1a expression reached a peak on day 21 after birth (P<0.05). Agtr2 expression gradually decreased to a low level after birth. Renin, Agtr1b, and Mas1 showed low expression in lung tissues at all developmental stages.

CONCLUSIONS

At different developmental stages of mice, ACE2 has dynamic expression changes, with high expression in early neonatal and adult mice. The other key molecules of the RAS pathway have their own expression patterns. These suggest that the difference in clinical features between children and adults with COVID-19 might be associated with the different expression levels of ACE2 in the different stages, and further studies are needed for the mechanism.

[Association of age distribution with the expression of angiotensin-converting enzyme 2 in lung tissues in severe acute respiratory syndrome coronavirus 2 infection: reflections from the study of RAS pathway expression in mice]

OBJECTIVE

To study the expression of angiotensin-converting enzyme 2 (ACE2) and other key molecules of the RAS pathway in normal mice at different developmental stages, and to provide ideas for understanding the infection mechanism of coronavirus disease 2019 (COVID-19) as well as the diagnosis and treatment of children with COVID-19.

METHODS

The mice at different developmental stages were enrolled, including fetal mice (embryonic days 14.5 and 18.5), neonatal mice (0, 3, 7, 14, and 21 days old), young mice (28 and 42 days old), and adult mice (84 days old). The lung tissues of all fetal mice from 4 pregnant mice were collected at each time point in the fetal group. Four mice were sampled in other age groups at each time point. Whole transcriptome resequencing was used to measure the mRNA expression of AGT, ACE, ACE2, Renin, Agtr1a, Agtr1b, Agtr2, and Mas1 in mouse lung tissue.

RESULTS

The expression of ACE2 in the lungs showed changes from embryonic stage to adult stage. It increased gradually after birth, reached a peak on day 3 after birth, and reached a nadir on day 14 after birth (P<0.05). The expression of AGT reached a peak on days 0 and 7 after birth and reached a nadir on day 21 after birth (P<0.05). The expression of ACE increased rapidly after birth and reached a peak on day 21 after birth (P<0.05). Agtr1a expression reached a peak on day 21 after birth (P<0.05). Agtr2 expression gradually decreased to a low level after birth. Renin, Agtr1b, and Mas1 showed low expression in lung tissues at all developmental stages.

CONCLUSIONS

At different developmental stages of mice, ACE2 has dynamic expression changes, with high expression in early neonatal and adult mice. The other key molecules of the RAS pathway have their own expression patterns. These suggest that the difference in clinical features between children and adults with COVID-19 might be associated with the different expression levels of ACE2 in the different stages, and further studies are needed for the mechanism.

The clinical dynamics of 18 cases of COVID-19 outside of Wuhan, China

Since an outbreak of 2019 novel coronavirus (COVID-19) in Wuhan and related regions in Hubei province, an increasing number of exported cases have been confirmed in other provinces in China and in multiple countries around the world with substantial morbidity and mortality [1–4]. The WHO has declared a public health emergency of international concern considering rapid increases in numbers of confirmed cases in China and additional countries. As of February 22, 2020, a total of 12 938 patients had been confirmed outside of Wuhan and related regions in Hubei province of China [1]. However, there is limited information about COVID-19 outside of Wuhan [5], and no study has reported the time to RT-PCR conversion and radiological changes after treatment.

The novel coronavirus can be transmitted from person to person with infection ranging from mild disease to severe pneumonia and radiological abnormalities on chest CT for most patients improved after RT-PCR conversion.

Allogeneic hematopoietic stem cell transplantation for Crohn disease complicated with myelodysplastic syndrome: A case report

RATIONALE

Myelodysplastic syndrome (MDS) can be complicated with Crohn disease (CD). Irritable bowel disease (IBD) associated with MDS has already been reported in the past; however, hematopoietic stem cell transplantation (HSCT) is rarely performed. Herein, we report a case of CD with MDS for HSCT.

PATIENT CONCERNS

A 41-year-old man was hospitalized due to abdominal pain and intermittent fever for 40 days. Two years later, he was readmitted due to abdominal pain and diarrhea with fever for 10 days.

DIAGNOSIS

Symptoms, laboratory examinations, and imaging findings of the patient were indicative of CD complicated with MDS.

INTERVENTIONS

An allogeneic HSCT was performed.

OUTCOMES

He died of severe lung infection 125 days post-transplantation.

LESSONS

The number of cases of CD combined with MDS remains insufficient, and no consensus opinions are available to date. Hence, HSCT is a very potential treatment method. Additional experiences are needed to determine its effectiveness.

Four pairs of alkaloid enantiomers from Isatis indigotica Fortune Ex Land with neuroprotective effects against H2O2-induced SH-SY5Y cell injury

In the current study, four pairs of new enantiomeric alkaloids (1a/1b-4a/4b) were obtained from the leaves of Isatis indigotica Fortune Ex Land. Their structures were elucidated through spectroscopic methods and quantum mechanical calculations. Biologically, all isolates were evaluated for their neuroprotective effects against H₂O₂-induced SH-SY5Y cell injury. As a result, 1a and 1b exhibited enantioselective neuroprotective effects, further Annexin V-FITC/PI analysis showed that apoptosis ratios of 1a and 1b were reduced to 20.93% and 17.87%, respectively.

Alkaloid Enantiomers from Isatis tinctoria with Neuroprotective Effects against H2O2-Induced SH-SY5Y Cell Injury

Six pairs of alkaloid enantiomers including 11 new alkaloids (1A: /1B: -5A: /5B, 6A: ) were isolated from the leaves of Isatis tinctoria. Their structures were established by extensive spectroscopic analyses. Enantiomers were separated successfully by chiral chromatographic column and the absolute configurations of all isolates were determined by comparison of experimental and calculated electronic circular dichroism spectra. The isolated alkaloids were evaluated for their neuroprotective activities against H₂O₂-induced cell injury in human neuroblastoma SH-SY5Y cells. The results showed that 5A/5B: and 6A/6B: exhibited potent neuroprotective activities at 50 µM compared with the H₂O₂-treated group.

A new dineolignan with anti-β-amyloid aggregation activity from the fruits of crataegus pinnatifida bge

A new dineolignan, crataeguslignan A (1), along with one known dineolignan (2) were isolated from the fruits of Crataegus pinnatifida Bge. Its chemical structure was identified by comprehensive spectroscopic analyses. All the isolated compounds were investigated with regard to their Aβ_1-42 inhibition activity. Among them, 1 displayed the most potent Aβ_1-42 inhibitory ability with the inhibition rate of 85.2% at the concentration of 20 μM.

Discovery of cycloneolignan enantiomers from Isatis indigotica Fortune with neuroprotective effects against MPP+-induced SH-SY5Y cell injury

A pair of new cycloneolignan enantiomers (1a and 1b) were isolated from the leaves of Isatis indigotica Fortune. Their structures were elucidated by extensive spectroscopic data analysis, including 1D and 2D NMR, HRESIMS, MS/MS analysis, together with theoretical electronic circular dichroism (ECD) calculations. Compounds 1a and 1b were then evaluated for their neuroprotective effects against MPP⁺-induced SH-SY5Y cell injury. As a result, compounds 1a (77.64%) and 1b (78.62%) exhibited moderate neuroprotective activity at the concentration of 12.5 µM compared with that of MPP⁺ treated group (62.00% at 1 mM) by MTT assay. Furthermore, Annexin V-FITC/PI analysis showed that apoptosis ratios of 1a and 1b were reduced to 10.99% and 9.31%, respectively.

Correction: Bioactive spiropyrrolizidine oxindole alkaloid enantiomers from Isatis indigotica fortune

Correction for 'Bioactive spiropyrrolizidine oxindole alkaloid enantiomers from Isatis indigotica fortune' by Si-Fan Liu et al., Org. Biomol. Chem., 2018, 16, 9430-9439.

Solitary nasopharynx metastasis from hepatocellular carcinoma after liver transplantation: A case report

RATIONALE

Hepatocellular carcinoma (HCC) is the fifth most common cancer and third leading cause of cancer-related deaths worldwide. Nasopharyngeal metastasis of hepatocellular carcinoma is very rare. This is the first report of posttransplantation nasopharyngeal metastasis.

PATIENT CONCERNS

A 45-year-old man with a history of hepatitis B related hepatocellular carcinoma (HCC) in the right segment of the liver received an orthotopic liver transplant. Two year after the transplantation, he suffered from severe headache, and head contrast enhanced CT scans did not show clues for brain or skull metastasis. Then he developed hoarseness and dysphagia.

DIAGNOSIS

The nasopharyngeal cancer was confirmed to be metastatic tumor from liver histologically according to biopsy.

INTERVENTIONS

This patient underwent radiotherapy (RT) of the metastatic nasopharyngeal tumor, and there was significant symptomatic relief.

OUTCOMES

The patient died 3 months after nasopharyngeal metastasis was diagnosed.

LESSONS

Recurrence of hepatocellular carcinoma with metastasis of nasopharyngeal carcinoma after liver transplantation is rare, but the prognosis is very poor. Close follow-up of patients should be paid attention to prevent the occurrence of such diseases.

A new coumarin from Juglans mandshurica Maxim induce apoptosis in hepatocarcinoma cells

In this study, a new coumarin, juglansoside C (1) was isolated from the bark of Juglans mandshurica. Its chemical structure was identified by comprehensive spectroscopic analyses. The in vitro cytotoxicity assay showed that 1 exhibited moderate cytotoxicity against human hepatocellular carcinoma Hep3B cells with an IC₅₀ value of 70.9 μM. Furthermore, Annexin V-FITC/PI staining assay indicated that 1 markedly induced apoptosis in Hep3B cells.

Bioactive spiropyrrolizidine oxindole alkaloid enantiomers from Isatis indigotica Fortune

Four pairs of new alkaloids, isatindigotindoline A–D, were isolated from Isatis indigotica, and were evaluated for their anti-Aβ1–42 aggregation effects.

Alkaloids from Juglans Mandshurica maxim induce distinctive cell death in hepatocellular carcinoma cells

The aim of this work was to further investigate the anticancer potential of Juglans mandshurica Maxim, including the separation of active constituents and their anti-proliferative effects with underlying mechanism of action. Five alkaloids (1-5) were isolated from the bark of J. mandshurica. Among them, 1 showed the highest cytotoxic activities against Hep3B and HepG2 cells with an IC50 values of 61.80 and 56.24 μM, respectively. Therefore, the cellular mechanism involved 1 was subsequently studied. Our results showed that 1 markedly caused apoptosis and autophagy, but without cell cycle arrest in HepG2 cells. Interestingly, only autophagic cell death was induced in 1-treated Hep3B cells. It is concluded that the isolated alkaloids exerted a certain anti-hepatoma potential, and our results may provide a basis for the further investigation of the alkaloids extracted from J. mandshurica.

Chemical constituents from the roots of Tripterygium wilfordii and their cytotoxic activity

In our ongoing search for bioactive constituents, a new sesquiterpene polyol ester, named triptersinine U (1), together with five known triterpenes (2-6) and seven sesquiterpene pyridine alkaloids (7-13), were isolated from the roots of Tripterygium wilfordii Hook. f. Their chemical structures were elucidated using extensive spectroscopic analyses, including 1D and 2D NMR, and HRESIMS, as well as comparison with previously reported data. Cytotoxic activities of all compounds 1-13 were evaluated against six human tumor cell lines (HepG2, Hep3B, Bcap37, U251, MCF-7 and A549) using the MTT in vitro assay. The results showed that triterpenes exhibited moderate cytotoxic activities toward the tested cell lines.

Food Byproducts as a New and Cheap Source of Bioactive Compounds: Lignans with Antioxidant and Anti-inflammatory Properties from Crataegus pinnatifida Seeds

During the process of manufacturing hawthorn (Crataegus pinnatifida) juice and jam, a significant quantity of byproducts (leaves, seeds) is generated. The antioxidant and anti-inflammatory bioassay-guided fractionation of the extract of hawthorn seeds has led to the isolation of eight new lignans, hawthornnins A-H (1-8), and seven known analogues (9-15). Their structures were elucidated by spectroscopic techniques, including 1D and 2D NMR and CD spectra. The radical-scavenging effects of all isolated compounds were investigated. 1-6 and 8 showed moderate activity against 2,2-diphenyl-1-picrylhydrazyl (DPPH), whereas 1-6 and 14 displayed good 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) free radical-scavenging activities that were even more potent than that of trolox. In addition, all isolates were evaluated for their anti-inflammatory activities by detecting the nitric oxide (NO) and tumor necrosis factor α (TNF-α) production by the LPS-induced murine macrophage cell line RAW264.7, and compounds 1-7, 13, and 14 exhibited potent inhibition of NO and TNF-α production. The structure-activity relationships of isolated lignans were also examined, and the results obtained show that C. pinnatifida seeds can be regarded as a potential new and cheap source of antioxidants and inflammation inhibitors.

Antioxidant and tyrosinase inhibitory effects of neolignan glycosides from Crataegus pinnatifida seeds

In our efforts to find an inhibitor of melanin formation and develop potential depigmenting agents for skin-protecting cosmetics and medicinal products from natural resources, we focused on the seeds of Crataegus pinnatifida which showed antioxidant and tyrosinase-inhibiting activities. By activity-guided fractionation of an extract of C. pinnatifida seeds, four new neolignan glycosides, pinnatifidaninsides A-D (1-4), along with two known compounds (5-6), were isolated. Their structures were elucidated by spectroscopic analyses, especially 1D, 2D NMR and CD spectra. The antioxidant and tyrosinase-inhibiting activities of all isolates were assayed. Compound 6 showed good activity against 2,2-diphenyl-1-pikrylhydrazyl, while compounds 1, 2, 5, and 6 exhibited strong 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) free radical scavenging activity, being as effective as, or even more effective than the positive control Trolox. Moreover, compounds 5 and 6 displayed a moderate mushroom tyrosinase inhibitory activity.

[Clinical and pathological analysis of 236 patients with primary extranodal lymphoma]

This study was aimed to analyze the clinical and pathological characteristics of patients with primary extranodal lymphoma (PENL). A total of 236 patients with PENL were enrolled to evaluate the clinical and pathological features. The clinical data of 236 patients with PENL confirmed by pathological and immunohistochemical methods between January 2001 and March 2012 were analyzed retrospectively. The results indicated that: (1)236 patients with PENL accounted for 40.7% of lymphoma over the same period. Median age was 55 years old (from 16 to 91 years old) . There were 153 males and 83 females(ratio 1.8: 1). (2)The common sites of involvement were gastrointestinal tract, nasal cavity, tonsil, mediastinum, skin, spleen, testis, bone and soft tissue, central nervous system, which accounted for 30.1% (71/236), 10.6% (25/236), 8.9% (21/236), 5.9% (14/236), 5.1% (12/236), 4.7% (11/236), 4.2% (10/236) , 4.2% (10/236) , 3.0% (7/236) respectively. (3)Symptoms of PENL did not have special characteristics, however its signs usually manifested with the enlargement or mass of organs, which accounted for 66.9% (158/236) in this study. (4)According to WHO classification of tumours of haematopoietic and lymphoid tissues in 2008, the common pathological type of gastrointestinal lymphoma was diffuse large B-cell lymphoma, mucosa-associated lymphoid tissue lymphoma; the common pathological type of nasal lymphoma was extranodal NK/T cell lymphoma; the common pathological type of tonsillar lymphoma, testicular lymphoma, CNS lymphoma was diffuse large B-cell lymphoma. It is concluded that the primary extranodal lymphoma is not rare, it is alert to PENL while organs enlarge or mass forms, so that clinical physician should pay attention to tissue biopsy.

Postoperative serum osteopontin level is a novel monitor for treatment response and tumor recurrence after resection of hepatitis B-related hepatocellular carcinoma

BACKGROUND

Presurgery serum osteopontin (OPN) level has been demonstrated to correlate to tumor recurrence and survival of hepatocellular carcinoma (HCC) patients. This study investigated the postoperative dynamic changes of serum OPN level and its clinical significance in HCC patients.

METHODS

Presurgery serum OPN levels were measured by enzyme-linked immunosorbent assay in cohort A of 179 HCC patients and were compared with the multiple controls including different kinds of liver diseases and healthy individuals. In cohort B of 110 patients with resectable HCCs, besides preoperative assays, serum OPN was monitored at 1 week, 1, and ≥2 months after operation.

RESULTS

The baseline presurgery serum OPN of HCC patients was significantly higher than that of the patients with the other kinds of liver diseases (p < 0.0001). The prognostic values of presurgery serum OPN level in HCC patients were further confirmed. The postsurgery OPN levels were significantly elevated within 1 week after HCC resection, then decreased at 1 month and reached the nadir later than 2 months after operations. It increased again at the time of tumor recurrence, then declined after the second removal of recurrent HCCs. Moreover, postoperative OPN in α-fetoprotein-negative and -positive HCC patients had the same changing pattern; it only correlated to liver function and C-reactive protein level.

CONCLUSIONS

After a transient fluctuation, serum OPN levels significantly decrease after curative resection of HCCs. Postoperative serum OPN could serve as a surrogate serologic biomarker for monitoring treatment response and tumor recurrence after HCC resection, including α-fetoprotein-negative ones.

Expression of a multifunctional Ca2+/calmodulin-dependent protein kinase and mutational analysis of its autoregulation

Autophosphorylation of multifunctional Ca2+/calmodulin-dependent protein kinase converts it from a Ca2(+)-dependent to a Ca2(+)-independent or autonomous kinase, a process that may underlie some long-term enhancement of transient Ca2+ signals. We demonstrate that the neuronal alpha subunit clone expressed in COS-7 cells (alpha-CaM kinase) is sufficient to encode the regulatory phenomena characteristic of the multisubunit kinase isolated from brain. Activity of alpha-CaM kinase is highly dependent on Ca2+/calmodulin. It is converted by autophosphorylation to an enzyme capable of Ca2(+)-independent (autonomous) substrate phosphorylation and autophosphorylation. Using site-directed mutagenesis, we separately eliminate five putative autophosphorylation sites within the regulatory domain and directly examine their individual roles. Ca2+/calmodulin-dependent kinase activity is fully retained by each mutant, but Thr286 is unique among the sites in being indispensable for generation of an autonomous kinase.

Distinct autophosphorylation sites sequentially produce autonomy and inhibition of the multifunctional Ca2+/calmodulin-dependent protein kinase

The multifunctional Ca2+/calmodulin-dependent protein kinase (multifunctional CaM kinase) may be an important mediator for neurotransmitters and hormones that utilize Ca2+ as a "second messenger." We examined the ability of autophosphorylation to convert the multifunctional CaM kinase to a Ca2+/calmodulin-independent (autonomous) form to determine whether autophosphorylation is a mechanism for short- or long-term enhancement of Ca2+ action. As the kinase incorporates phosphate during continuous stimulation by Ca2+/calmodulin, its ability to phosphorylate exogenous substrates becomes increasingly autonomous. Withdrawal of Ca2+ after a critical level of phosphate incorporation is reached leads to a "burst" or rapid increase in Ca2+-independent autophosphorylation. The "burst" of autophosphorylation is distinct from the initial Ca2+-dependent autophosphorylation, however, since it inhibits substrate phosphorylation. Both Ca2+-dependent and Ca2+-independent substrate phosphorylation are inhibited by this autonomous autophosphorylation. Thus, autophosphorylation has a dual role in modulating the activity of multifunctional CaM kinase. It initially enables the kinase to continue phosphorylating substrates after Ca2+ levels decline, but it eventually suppresses this autonomous activity. Tryptic phosphopeptide mapping demonstrates that appearance of phosphothreonine-containing peptides is common to several conditions used to generate an autonomous enzyme. Sequencing reveals the critical "autonomy" site to be threonine286. The inhibitory mode of autophosphorylation involves 3 additional phosphopeptides containing a serine and a threonine residue.

Multifunctional Ca2+/calmodulin-dependent protein kinase: domain structure and regulation

Cells respond to many hormones, neurotransmitters and growth factors by increasing intracellular Ca2+. This second messenger, in turn, affects cellular function via activation of a novel multifunctional Ca2+/calmodulin-dependent protein kinase. The kinase displays an interesting form of biochemical 'memory'; activation elicits an autophosphorylation which converts it to a Ca2+-independent enzyme that can continue to phosphorylate cellular proteins for some time following termination of the initial Ca2+ stimulus.

The stereospecificity of protein kinases

To test whether cellular protein kinases exist that phosphorylate D-amino acid residues, a method was developed for separating O-phospho-D-serine from O-phospho-L-serine and O-phospho-L-tyrosine from O-phospho-D-tyrosine. This was accomplished by converting these amino acids to the L-leucyl dipeptide derivatives followed by separation of the diastereomers by anion-exchange high-performance liquid chromatography. The enantiomeric content of these D- and L-residues were measured in hydrolysates of 32P-labeled proteins produced by the protein kinases of human erythrocytes and the tyrosyl protein kinase of the Abelson leukemia virus. We found no measurable D-phosphoserine in erythrocyte membrane proteins under conditions where a 1% content of this residue relative to L-phosphoserine would have been detected. These values can be used to place an upper hypothetical limit on the fraction of erythrocyte protein kinase activity that is specific for serine residues in the D-configuration. In separate experiments, we examined the specificity of the tyrosyl protein kinases. We found that all of the phosphotyrosine that we isolated from the erythrocyte band 3 NH2-terminal fragment and from the autophosphorylation of the Abelson virus tyrosyl kinase was in the L-configuration.

Enzymatic methylation of band 3 anion transporter in intact human erythrocytes

Band 3, the anion transport protein of erythrocyte membranes, is a major methyl-accepting substrate of the intracellular erythrocyte protein carboxyl methyltransferase (S-adenosyl-L-methionine: protein-D-aspartate O-methyltransferase; EC 2.1.1.77) [Freitag, C., & Clarke, S. (1981) J. Biol. Chem. 256, 6102-6108]. The localization of methylation sites in intact cells by analysis of proteolytic fragments indicated that sites were present in the cytoplasmic N-terminal domain as well as the membranous C-terminal portion of the polypeptide. The amino acid residues that serve as carboxyl methylation sites of the erythrocyte anion transporter were also investigated. 3H-Methylated band 3 was purified from intact erythrocytes incubated with L-[methyl-3H]methionine and from trypsinized and lysed erythrocytes incubated with S-adenosyl-L-[methyl-3H]methionine. After proteolytic digestion with carboxypeptidase Y, D-aspartic acid beta-[3H]methyl ester was isolated in low yields (9% and 1%, respectively) from each preparation. The bulk of the radioactivity was recovered as [3H]methanol, and the amino acid residue(s) originally associated with these methyl groups could not be determined. No L-aspartic acid beta-[3H]methyl ester or glutamyl gamma-[3H]methyl ester was detected. The formation of D-aspartic acid beta-[3H]methyl esters in this protein in intact cells resulted from protein carboxyl methyltransferase activity since it was inhibited by adenosine and homocysteine thiolactone, which increases the intracellular concentration of the potent product inhibitor S-adenosylhomocysteine, and cycloleucine, which prevents the formation of the substrate S-adenosyl-L-[methyl-3H]methionine.

Activation of the multifunctional Ca2+/calmodulin-dependent protein kinase by autophosphorylation: ATP modulates production of an autonomous enzyme

The multifunctional Ca2+/calmodulin-dependent protein kinase purified from rat brain cytosol undergoes an intramolecular self-phosphorylation or autophosphorylation. Autophosphorylation produces two strikingly different effects on kinase activity that are dependent on the level of ATP used in the reaction. At low but saturating levels of ATP (5 microM), autophosphorylation causes a 75% reduction in kinase activity, with the residual activity still retaining a dependence on Ca2+ and calmodulin. By contrast, at high but physiological levels of ATP (500 microM), the kinase is converted by autophosphorylation to a form that is autonomous of Ca2+ and calmodulin, with no accompanying reduction in activity. The extent of phosphate incorporation does not determine whether the kinase becomes inhibited or autonomous. Autophosphorylated kinase shows the functional change characteristic of the ATP concentration used during the reaction--inhibited at low ATP and autonomous at high ATP--even when compared at the same level of incorporated phosphate. ATP appears to regulate the site(s) phosphorylated during activation of the kinase and thereby modulates the dual effects of autophosphorylation. Events triggered by transient elevations of cellular Ca2+ may be potentiated and retained by generation of the Ca2+/calmodulin-independent protein kinase activity.

Carboxyl methylation of human erythrocyte band 3 in intact cells. Relation to anion transport activity

The anion transport protein of the human erythrocyte membrane, band 3, is reversibly methylated by an endogenous protein carboxyl methyltransferase. The physiological consequence of this modification was studied by measuring the rate of phosphate transport by intact erythrocytes incubated under conditions where protein methylation reactions are inhibited. No change in phosphate transport was detected when cells were treated with either methionine-free media or cycloleucine, whereas cells incubated with adenosine and homocysteine thiolactone displayed a marginally slower rate of transport, which was not reversed by subsequent remethylation of the membrane proteins. These results suggest that erythrocyte protein carboxyl methylation does not directly regulate this activity of band 3.