Papillary Renal Cell Carcinoma: Evolving Classification by Combined Morphologic and Molecular Means

Papillary renal cell carcinoma classification has evolved as a result of attentive morphologic observations by pathologists coupled with specific immunohistochemical, molecular, and clinical data. Refinement of this relatively common diagnostic category of renal neoplasia has resulted in the parsing out of specific renal cell carcinoma subtypes that no longer belong in the papillary renal cell carcinoma category and can have distinct familial and prognostic implications (eg, fumarate hydratase (FH)-deficient renal cell carcinomas). In addition, evolving classification has enabled more accurate diagnosis by surgical pathologists (through the description of recognizable morphologic variants). In many cases, molecular findings have aided and confirmed morphologic categorization. The combination of morphologic and molecular findings continues to provide important prognostic information for patients and their clinicians.

Update on Selected High-grade Renal Cell Carcinomas of the Kidney: FH-deficient, ALK-rearranged, and Medullary Carcinomas

High-grade renal cell carcinoma (RCC), often diagnosed at advanced stages, significantly contributes to renal cancer-related mortality. This review explores the progress in understanding specific subtypes of high-grade RCC, namely fumarate hydratase (FH)-deficient RCC, anaplastic lymphoma kinase (ALK)-rearranged RCC, and SMARCB1-deficient renal medullary carcinoma, all of which are now recognized as molecularly defined entities in the WHO classification system (2022). While these entities each exhibit a morphologic spectrum that overlaps with other high-grade RCC, ancillary tools developed based on their distinctive molecular alterations can help establish a specific diagnosis, underscoring the importance of integrating molecular findings into diagnostic paradigms. It is important to exclude these specific tumor types in cases with similar morphologic spectrum before rendering a diagnosis of high-grade papillary RCC, collecting duct carcinoma, or RCC, NOS. Several gray areas exist within the spectrum of high-grade uncommon types of RCC, necessitating continued research to enhance diagnostic precision and therapeutic options.

[Expression of programmed cell death ligand 1 and clinicopathological and immunological characteristics in fumarate hydratase-deficient renal cell carcinoma]

Objective: To investigate the expression of programmed cell death ligand 1 (PD-L1), clinicopathologic features, immunohistochemical expression and molecular characteristics in fumarate hydratase (FH)-deficient renal cell carcinoma and to explore the potential application of immunotherapy in the patients. Methods: There were six patients with FH-deficient renal cell carcinoma treated at the First Affiliated Hospital of Fujian Medical University between January 2020 and October 2022. The clinical data, histological morphology, immunophenotype, PD-L1 expression and next-generation sequencing results were tabulated and analyzed. Results: There were 6 patients, all male, age ranged from 37 to 72 years (mean 45.7 years). Four cases were high-grade (WHO/ISUP grade3-4) with 2 or more histologic patterns, including papillary (most common), glandular, tubular, vesicular, ethmoid, nest-like, cystic and solid structures. Two cases were low-grade which showed nest-like, glandular, or tubular arrangement with eosinophilic flocculent cytoplasm and small intracellular vacuoles. Immunohistochemical analysis revealed strong expression of 2SC in all 6 cases, negative expression of FH in 5 cases, and positive expression of GATA3 in 5 cases. In high-grade cases, the mean values of CD4 and CD8 positive T-lymphocytes in advanced tumor invasion were 180.3/mm2 and 130.5/mm2, respectively. PD-L1 combined positive scores (CPS) were 20, 50, 5 and 30, respectively. The Ki-67 proliferative index were 20%, 20%, 10% and 30%, respectively. In low-grade cases, the mean values of CD4 and CD8 positive T-lymphocytes were 123.0/mm2 and 100.5/mm2, respectively. The PD-L1 CPS score was 1, and the Ki-67 proliferation index was 3%. High-throughput sequencing showed FH gene somatic mutation in 3 cases, FH gene germline mutation in 2 cases, and FH gene mutation was not detected in one case. Conclusion: FH-deficient renal cell carcinoma is more commonly high-grade than low grade. FH and 2SC are immunohistochemical markers used in the diagnosis of FH-deficient renal cell carcinoma, and GATA3 positivity is supportive of the diagnosis. The tumor infiltration of high-grade FH-deficient renal cell carcinoma shows an increase in CD4 and CD8 positive T-lymphocytes, and high expression of PD-L1; thus, anti-PD-L1 immunotherapy can be used as a treatment option.

Intense FDG Uptake in Leiomyomatosis Peritonealis Disseminata With Fumarate Hydratase Deficiency

ABSTRACT

A 35-year-old woman with a history of laparoscopic myomectomy presented with repeated abdominal pain. Contrast-enhanced abdominal and pelvic CT showed multiple enhancing solid or mixed cystic and solid peritoneal masses, and an enhancing uterine mass. All these masses showed intense FDG uptake on FDG PET/CT. The intraperitoneal and uterine masses were surgically removed. The histological and immunohistochemical findings of the peritoneal lesions were consistent with leiomyomatosis peritonealis disseminata with fumarate hydratase deficiency, and the uterine mass was adenomyosis. This case indicates fumarate hydratase-deficient extrauterine leiomyoma can show intense FDG uptake mimicking malignancy.

Comparative analyses of tumour immune microenvironment between collecting duct carcinoma and fumarate hydratase-deficient renal cell carcinoma

AIMS

Collecting duct carcinoma (CDC) and fumarate hydratase-deficient renal cell carcinoma (FH-deficient RCC) have similar histological morphologies and both show a poor prognosis. Programmed death ligand 1 (PD-L1) inhibitor has been approved for the treatment of RCC. However, tumour-infiltrating neutrophils stimulated by interleukin-8 (IL-8) interfere with PD-L1 inhibitors. Here, we retrospectively analysed PD-L1 and IL-8 expression, and examined its relationship with infiltrating immune cells.

METHODS

Nine cases of CDC and seven cases of FH-deficient RCC were selected. We defined PD-L1 and IL-8 expression by the Tumour Proportion Score and Combined Positive Score (CPS). We counted the numbers of CD8+, CXCR2+, CD11b+, CD66b+ and CD33+ immune cells located in the tumour components.

RESULTS

A number of CXCR2+ (p=0.0058), CD11b+ (p=0.0070) and CD66b+ (p=0.0067) immune cells infiltrating into CDC were significantly higher than those infiltrating into FH-deficient RCC. In CDC, PD-L1 expression was correlated with a high density of CD8+ lymphocytes (p=0.0389), but was not in FH-deficient RCC (p=0.6985). IL-8 CPS was significantly higher in CDC than in FH-deficient RCC (p=0.0069). In addition, among the CDC cases, IL-8 CPS showed significant positive correlations with CXCR2+, CD11b+ and CD66b+ immune cell densities (p=0.0250, p=0.0104 and p=0.0374, respectively), whereas FH-deficient RCC showed no significant correlations between IL-8 CPS and immune cell densities.

CONCLUSIONS

Our results suggest the difference of each tumour microenvironment between CDC and FH-deficient RCC, and IL-8 is a potential therapeutic target for treating CDC, but not FH-deficient RCC.

Factors influencing the detection rate of fumarate peak in 1H MR spectroscopy of fumarate hydratase-deficient renal cell carcinoma at 3 T MRI

AIM

To identify factors that may be associated with fumarate detection rate in 1H-magnetic resonance spectroscopy (MRS) in fumarate hydratase-deficient renal cell carcinoma (FH-RCC).

MATERIALS AND MEHODS

Between February 2018 and March 2022, 16 FH-RCC patients with 30 lesions underwent 1H-MRS. Detection results were classified as having a detected fumarate peak (n=12), undetected peak (n=10), or technical failure (n=8). Factors including tumour size, tumour location, treatment history, and metastasis status were collected and analysed. A Bayesian logistic regression model was applied to evaluate the association between these factors and the detection result.

RESULTS

Bayesian analysis demonstrated significant associations between fumarate detection results and the following factors: long-axis diameter (odds ratio [OR] of 1.64; 95% confidence interval [CI] of 1.07-2.53), short-axis diameter (OR of 1.90; 95% CI of 1.19-3.06), voxel size (OR of 2.85; 95% CI of 1.70-4.75), treatment history (OR of 0.35; 95% CI of 0.21-0.58), non-metastatic state (OR of 2.45; 95% CI of 1.48-4.06), and lymph node metastasis (OR of 0.35; 95% CI of 0.21-0.58). Technical failure results were associated with factors such as treatment history (OR of 2.59; 95% CI of 1.37-4.66), non-metastatic state (OR of 0.36; 95% CI of 0.19-0.66), and lymph node metastasis (OR of 2.61; 95% CI of 1.39-4.74).

CONCLUSION

Tumour size, treatment history, and metastasis character were associated with the detection of abnormal fumarate accumulation. This finding will serve as a reference for interpreting 1H-MRS results and for selecting suitable scenarios to evaluate FH-RCC.

Serum Anti-Fumarate Hydratase Autoantibody as a Biomarker for Predicting Prognosis of Acute-on-Chronic Liver Failure

Background/Aims

To investigate the autoantibody against fumarate hydratase (FH), which is a specific liver failure-associated antigen (LFAA) and determine whether it can be used as a biomarker to evaluate the prognosis of acute-on-chronic liver failure (ACLF).

Methods

An immunoproteomic approach was applied to screen specific LFAAs related to differential prognosis of ACLF (n=60). Enzyme-linked immunosorbent assay (ELISA) technology was employed for the validation of the frequency and titer of autoantibodies against FH in ACLF patients with different prognoses (n=82). Moreover, we clarified the expression of autoantibodies against FH in patients with chronic hepatitis B (n=60) and hepatitis B virus-related liver cirrhosis (n=60). The dynamic changes in the titers of autoantibodies against FH were analyzed by sample collection at multiple time points during the clinical course of eight ACLF patients with different prognoses.

Results

Ultimately, 15 LFAAs were screened and identified by the immunoproteomic approach. Based on ELISA-based verification, anti-FH/Fumarate hydratase protein autoantibody was chosen to verify its expression in ACLF patients. ACLF patients had a much higher anti-FH autoantibody frequency (76.8%) than patients with liver cirrhosis (10%, p=0.000), patients with chronic hepatitis B (6.7%, p=0.022), and normal humans (0%, p=0.000). More importantly, the frequency and titer of anti-FH protein autoantibodies in the serum of ACLF patients with a good prognosis were much higher than that of patients with a poor prognosis (83.9% vs 61.5%, p=0.019; 1.41±0.85 vs 0.94±0.56, p=0.017, respectively). The titer of anti-FH autoantibodies showed dynamic changes in the clinical course of ACLF.

Conclusions

The anti-FH autoantibody in serum may be a potential biomarker for predicting the prognosis of ACLF.

Rutaecarpine induces the differentiation of triple-negative breast cancer cells through inhibiting fumarate hydratase

BACKGROUND

Triple-negative breast cancer (TNBC) is one of the most aggressive human cancers and has poor prognosis. Approximately 80% of TNBC cases belong to the molecular basal-like subtype, which can be exploited therapeutically by inducing differentiation. However, the strategies for inducing the differentiation of TNBC remain underexplored.

METHODS

A three-dimensional (3D) morphological screening model based on a natural compound library was used to identify possible candidate compounds that can induce TNBC cell differentiation. The efficacy of rutaecarpine was verified using assays: RT-qPCR, RNA-seq, flow cytometry, immunofluorescence, SCENITH and label-free LC-MS/MS. The direct targets of rutaecarpine were identified through drug affinity responsive target stability (DARTS) assay. A xenograft mice model was also constructed to confirm the effect of rutaecarpine in vivo.

RESULTS

We identified that rutaecarpine, an indolopyridoquinazolinone, induces luminal differentiation of basal TNBC cells in both 3D spheroids and in vivo mice models. Mechanistically, rutaecarpine treatment leads to global metabolic stress and elevated ROS in 3D cultured TNBC cells. Moreover, NAC, a scavenger of ROS, impedes rutaecarpine-induced differentiation of TNBC cells in 3D culture. Finally, we identified fumarate hydratase (FH) as the direct interacting target of rutaecarpine. The inhibition of FH and the knockdown of FH consistently induced the differentiation of TNBC cells in 3D culture.

CONCLUSIONS

Our results provide a platform for differentiation therapy drug discovery using 3D culture models and identify rutaecarpine as a potential compound for TNBC treatment.

68Ga-PSMA PET/CT versus 18F-FDG PET/CT for detecting lesions in a case of fumarate hydratase-deficient renal cell carcinoma

Gallium-68 (68Ga)-prostate-specific membrane antigen (PSMA) positron emission tomography/computed tomography (PET/CT) and fluorine-18-fluorodeoxyglucose(18F-FDG) PET/CT were performed for staging in a 51-year-old man with renal cell carcinoma. Compared with 18F-FDG PET/CT, no obvious tracer uptake in right renal mass and less metastatic lesions were found on 68Ga-PSMA PET/CT. Postoperative pathology demonstrated the diagnosis of fumarate hydratase-deficient renal cell carcinoma (FHRCC).

Conditional Covalent Lethality Driven by Oncometabolite Accumulation

Hereditary leiomyomatosis and renal cell carcinoma (HLRCC) is a cancer predisposition syndrome driven by mutation of the tumor suppressor fumarate hydratase (FH). Inactivation of FH causes accumulation of the electrophilic oncometabolite fumarate. In the absence of methods for reactivation, tumor suppressors can be targeted via identification of synthetic lethal interactions using genetic screens. Inspired by recent advances in chemoproteomic target identification, here, we test the hypothesis that the electrophilicity of the HLRCC metabolome may produce unique susceptibilities to covalent small molecules, a phenomenon we term conditional covalent lethality. Screening a panel of chemically diverse electrophiles, we identified a covalent ligand, MP-1, that exhibits FH-dependent cytotoxicity. Synthesis and structure-activity profiling identified key molecular determinants underlying the molecule's effects. Chemoproteomic profiling of cysteine reactivity together with clickable probes validated the ability of MP-1 to engage an array of functional cysteines, including one lying in the Zn-finger domain of the tRNA methyltransferase enzyme TRMT1. TRMT1 overexpression rescues tRNA methylation from inhibition by MP-1 and partially attenuates the covalent ligand's cytotoxicity. Our studies highlight the potential for covalent metabolites and small molecules to synergistically produce novel synthetic lethal interactions and raise the possibility of applying phenotypic screening with chemoproteomic target identification to identify new functional oncometabolite targets.

Alterations in Primary Carbon Metabolism in Cucumber Infected with Pseudomonas syringae pv lachrymans: Local and Systemic Responses

The reconfiguration of the primary metabolism is essential in plant–pathogen interactions. We compared the local metabolic responses of cucumber leaves inoculated with Pseudomonas syringae pv lachrymans (Psl) with those in non-inoculated systemic leaves, by examining the changes in the nicotinamide adenine dinucleotides pools, the concentration of soluble carbohydrates and activities/gene expression of carbohydrate metabolism-related enzymes, the expression of photosynthesis-related genes, and the tricarboxylic acid cycle-linked metabolite contents and enzyme activities. In the infected leaves, Psl induced a metabolic signature with an altered [NAD(P)H]/[NAD(P)⁺] ratio; decreased glucose and sucrose contents, along with a changed invertase gene expression; and increased glucose turnover and accumulation of raffinose, trehalose, and myo-inositol. The accumulation of oxaloacetic and malic acids, enhanced activities, and gene expression of fumarase and l-malate dehydrogenase, as well as the increased respiration rate in the infected leaves, indicated that Psl induced the tricarboxylic acid cycle. The changes in gene expression of ribulose-l,5-bis-phosphate carboxylase/oxygenase large unit, phosphoenolpyruvate carboxylase and chloroplast glyceraldehyde-3-phosphate dehydrogenase were compatible with a net photosynthesis decline described earlier. Psl triggered metabolic changes common to the infected and non-infected leaves, the dynamics of which differed quantitatively (e.g., malic acid content and metabolism, glucose-6-phosphate accumulation, and glucose-6-phosphate dehydrogenase activity) and those specifically related to the local or systemic response (e.g., changes in the sugar content and turnover). Therefore, metabolic changes in the systemic leaves may be part of the global effects of local infection on the whole-plant metabolism and also represent a specific acclimation response contributing to balancing growth and defense.

Comparison of 2SC, AKR1B10, and FH Antibodies as Potential Biomarkers for FH-deficient Uterine Leiomyomas

Hereditary leiomyomatosis and renal cell cancer (HLRCC) is a tumor predisposition syndrome caused by germline fumarate hydratase (FH) mutations and characterized by uterine and cutaneous leiomyomas and renal cell cancer. Currently, there is no generally approved method to differentiate FH-deficient uterine leiomyomas from other leiomyomas. Here, we analyzed 3 antibodies (S-(2-succino)-cysteine [2SC], aldo-keto reductase family 1, member B10 [AKR1B10], and FH) as potential biomarkers. The study consisted of 2 sample series. The first series included 155 formalin-fixed paraffin-embedded uterine leiomyomas, of which 90 were from HLRCC patients and 65 were sporadic. The second series included 1590 unselected fresh frozen leiomyomas. Twenty-seven tumors were from known HLRCC patients, while the FH status for the remaining 1563 tumors has been determined by copy number analysis and Sanger sequencing revealing 45 tumors with monoallelic (n=33) or biallelic (n=12) FH loss. Altogether 197 samples were included in immunohistochemical analyses: all 155 samples from series 1 and 42 available corresponding formalin-fixed paraffin-embedded samples from series 2 (15 tumors with monoallelic and 7 with biallelic FH loss, 20 with no FH deletion). Results show that 2SC performed best with 100% sensitivity and specificity. Scoring was straightforward with unambiguously positive or negative results. AKR1B10 identified most tumors accurately with 100% sensitivity and 99% specificity. FH was 100% specific but showed slightly reduced 91% sensitivity. Both FH and AKR1B10 displayed also intermediate staining intensities. We suggest that when patient's medical history and/or histopathologic tumor characteristics indicate potential FH-deficiency, the tumor's FH status is determined by 2SC staining. When aberrant staining is observed, the patient can be directed to genetic counseling and mutation screening.

Fumarate hydratase deficient renal cell carcinoma and fumarate hydratase deficient-like renal cell carcinoma: Morphologic comparative study of 23 genetically tested cases

Hereditary leiomyomatosis and renal cell carcinoma-associated renal cell carcinoma (HLRCC)/ fumarate hydratase deficient renal cell carcinoma (FHRCC) is an aggressive tumor defined by molecular genetic changes - alteration in fumarate hydratase (FH) gene. The morphologic spectrum of HLRCC/FHDRCC is remarkably variable. The presence of large nuclei and prominent dark red inclusion-like nucleoli and perinucleolar clearing are considered as helpful morphologic clue. We selected 23 renal neoplasms primarily based on their morphologic features suspicious for HLRCC/FHDRCC. Morphological, basic immunohistochemical, and genetic analysis was performed. The tumors were divided in two groups according to the molecular genetic findings. The first group included 13 tumors with detected FH mutation/LOH (compatible with diagnosis FHRCC), and the second group included 10 tumors without FH mutation/LOH (FH-like RCCs). In the FHRCC group, the vast majority of cases (9/13) had mixed morphology with different architectural growth patterns. All cases showed prominent macronucleoli, and perinucleolar clearing was found in 10/13 cases. Immunohistochemically, 6/7 FHRCC cases were negative for FH antibody, while one case showed strong diffuse FH reactivity. The FH-like RCC group showed more uniform architectural growth pattern. All 10 tumors had prominent macronucleoli, and perinucleolar clearing was present in 8/10 cases. Eight FH-like RCC cases showed diffuse strong positivity for FH, although 2 cases were completely negative for FH. It is evident that neither morphologic feature nor immunohistochemical analysis can be reliably used in routine practice for the diagnosis of HLRCC/FHRCC. In suspected cases, the diagnosis of HLRCC/FHRCC can be confirmed by molecular-genetic testing for FH mutation. It should be noted that the traditionally described morphologic features of HLRCC/FHRCC (prominent eosinophilic macronuclei with perinucleolar halos) can frequently be seen in other renal neoplasms.

MECHANISMS IN THE INHIBITION OF MICROORGANISMS BY SORBIC ACID

York, George K. (University of California, Davis), and Reese H. Vaughn. Mechanisms in the inhibition of microorganisms by sorbic acid. J. Bacteriol. 88:411-417. 1964.-Oxidative assimilation of glucose, acetate, succinate, and fumarate by washed cells of Escherichia coli, Pseudomonas aeruginosa, and Saccharomyces cerevisiae was inhibited by concentrations of sorbic acid ranging from 15 to 105 mg per 100 ml. At higher concentrations, the oxidation of these substrates was inhibited. Oxidative phosphorylation by submicroscopic particles of E. coli was reduced by about 30% by 37 mg per 100 ml of sorbic acid. The sulfhydryl enzymes fumarase, aspartase, and succinic dehydrogenase were inhibited by sorbic acid. The loss of activity of sorbic acid after reacting with cysteine suggested that a thiol addition occurred, which is believed to be the mechanism of action against sulfhydryl enzymes or cofactors.

EVIDENCE FOR A TRICARBOXYLIC ACID CYCLE IN MYCOPLASMA HOMINIS

VanDemark, P. J. (Cornell University, Ithaca, N.Y.), and P. F. Smith. Evidence for a tricarboxylic acid cycle in Mycoplasma hominis. J. Bacteriol. 88:1602-1607. 1964.-Resting cells of acetate-grown Mycoplasma hominis strain 07 oxidized the various intermediates of the tricarboxylic and glyoxylate cycles, with the exception of sodium citrate and glyoxylate. Extracts of these cells possessed isocitric dehydrogenase, isocitratase, alpha-ketoglutaric dehydrogenase, succinic dehydrogenase, fumarase, malic dehydrogenase, citratase, and acetyl coenzyme A kinase activities. With the assay conditions employed, condensing enzyme, malate synthetase, and phosphotransacetylase activities were negligible. Incubation of sodium acetate-2-C(14) with the various intermediates of the tricarboxylic acid cycle in the presence of cell-free extracts resulted in exchange of the isotope with these compounds as well as the formation of other labeled intermediates of the tricarboxylic acid cycle. Oxidation of sodium acetate-2-C(14) alone resulted in the formation of labeled succinate, fumarate, and malate.

Acetate catabolism in the dissimilatory iron-reducing isolate GS-15

Acetate-grown GS-15 whole-cell suspensions were disrupted with detergent and assayed for enzymes associated with acetate catabolism. Carbon monoxide dehydrogenase and formate dehydrogenase were not observed in GS-15. Catabolic levels of acetokinase and phosphotransacetylase were observed. Enzyme activities of the citric acid cycle, i.e., isocitrate dehydrogenase, 2-oxoglutarate sythase, succinate dehydrogenase, fumarase, and malate dehydrogenase, were observed.

An enzymatic method for the assay of serum argininosuccinate lyase

A rapid enzymatic method was developed for the assay of serum argininosuccinate lyase (ASAL: EC 4.3.2.1) which is a useful marker enzyme for diagnosis of parenchymal liver diseases. Fumarate, liberated from argininosuccinate in the lyase-mediated reaction, was converted to pyruvate via L-malate by the actions of fumarase and malic enzyme in the presence of NADP+. The NADPH formed was then oxidized with a diaphorase-resazurin system to give a highly fluorescent resorufin. All the enzymatic reactions proceeded continuously in 0.1 M Tris-HCl buffer (pH 7.5) and allowed direct assay of ASAL in serum by monitoring the increase in the fluorescence intensity due to resorufin. The method is rapid and sensitive; only 50 microliter of serum is required. This method was used to detect increases in the activities in sera from patients with liver diseases.

Determination of the isotope distribution in malate-14C with fumarase-negative lactic acid bacteria

No fumarase activity could be found in whole cells or in cell-free crude extracts from Leuconostoc mesenteroides or Lactobacillus curvatus. The degradation of L-malate-4-14C by these organisms yielded more than 95% of the label as 14CO2. It is therefore recommended that these organisms, rather than Lactobacillus plantarum, should be used in the determination of isotope distribution in L-malate-14C, since L. plantarum exhibits a significant fumarase activity and thus randomizes malate prior to the decarboxylation of this substance by the malolactic enzyme.

Enzymic generation of chiral acetates. A quantitative evaluation of their configurational assay

1. R-Acetate was generated enzymically from R-acetate in the sequence acetate leads to malate leads to oxaloacetate leads to acetate, and S-acetate likewise from S-acetate. It was concluded that the formation of malate on malate synthase involves the operation of a normal isotopic effect combined with inversion of configuration. The malate synthase kH/k2H was determined as 3.7 +/- 0.5 by a method which yields results independently of the stereochemical purity of the chiral acetates used initially. 2. R-Acetate was also generated from R-acetate in the sequence acetate leads to citrate leads to malate leads to oxaloacetate leads to acetate, and S-acetate likewise from S-acetate. The conclusion is the same as given above, but refers to the formation of citrate on the re-synthase. 3. 2S,3R-[2-2H1,3-2H1,3H1]Malate and 2S,3S-[2-2H1,3-2H1]malate were prepared from 2S-[2,3-2H3]malate by treatment with fumarase in tritiated water and normal water, respectively. It was assumed that these malate specimens were pure with respect to chirality as generated by isotopic labelling. 4. These two malate specimens were partially converted (about 9%) to acetates in conditions where no racemization at the level of transiently formed oxaloacetate occurred. That no racemization took place was demonstrated experimentally. Oxidative enzymic hydrolysis of 2S,3R-[2-2H1,3-2H1,3H1]malate in normal water and of 2S,3S-[2-2H1,3-2H1]malate in tritiated water produced S-[2H1,3H1]acetate and R-[2H1,3H1]acetate, respectively. 5. The isolated R-[2H1,3H1]acetate and S-[2H1,3H1]acetate on configurational analysis yielded malates which in the presence of fumarase retained 79.7 +/- 0.7% and 20.3 +/- 0.9%, respectively, of their total tritium content. The symmetric deviation from the 50% value found with [3H1]acetate strengthens the conclusion that stereochemically pure chiral acetates were analyzed. The malate synthase kH/k2H was determined from the data of this study as 3.9 +/- 0.2. 6. The average of the values given under paragraphs 1 and 5 for the isotopic discrimination on malate synthase corresponds to kH/k2H=3.8 +/- 0.1. It was concluded that the configurational analysis of stereochemically pure R-[2H1,3H1]acetate and S-[2H1,3H1]acetate yields malates which in the presence of fumarase retain 79 +/- 2% and 21 +/- 2%, respectively, of their total tritium content. Hence, a deviation of 29 +/- 2% from the 50% value represents the actual amplitude of the configurational assay. 7. Outlines are given for an enzymic generation of chiral acetates in preparative scale.

Preparation and characterization of rabbit IgG fractions

Rabbit IgG has been purified and further fractionated by deae-cellulose column chromatography to yield three fractions, Fr-I,-II and -III-1 that span a broad range in the heterogeneous molecular population of IgG. Immunodiffusion established that these fractions are free from contamination by IgA, IgM, transferrin, and hemopexin. The three fractions were assayed for neutral hexose and sialic acid; Fr-III-1 and Fr-I yielded the highest and lowest values for these components, resepctively. The order of elution from DEAE-cellulose and the electrophoretic mobilities of the fractions correlate with their content of sialic acid. Digestion of Fr-I with papain is much more rapid and complete than that of Fr-III-1. Treatment with neuraminidase to remove sialic acid from each fraction does not affect the comparative susceptibility to digestion by papain. The fractions can also be distinguished by the relative amounts of H-L half molecules and H chains formed under identical conditions of reduction with cysteine and by differences in their ability to bind with IgG receptors on the fetal rabbit yolk sac membrane. The results are discussed in the context of the structures of IgG in the heterogeneous population of molecules and the possible relation to the oligosaccharide moieties of the IgG molecules in that population.

Substrate stereochemistry of the acetyl-CoA acetyltransferase reaction

1. A specimen of symmetrically tritiated 3S-3-hydroxy[2-3H2]butyryl-CoA was prepared from acetoacetyl-CoA by incubation in tritiated water, followed by enzymic reduction using 3S-specific 3-hydroxyacyl-CoA dehydrogenase. In addition, a specimen of dideuterated, racemic 3RS-3-hydroxy-[2-2H2]butyryl-CoA was prepared chemically from 3RS-3-hydroxy[2-2H2]butyric acid. 2. These acyl-CoA derivatives were incubated respectively with deuterium oxide and tritated water in presence of enoyl-CoA hydratase. Stereospecifically tritiated compounds, respectively 2S,3S-3-hydroxy[2-2H1,3H1]butyryl-CoA and 2R,3S-3-hydroxy[2-1H1,3H1]butyryl-CoA (plus 3R-diastereomer) were formed and isolated. 3. 3S-3-Hydroxy[2-3H2]butyryl-CoA and the 3S-[2-3H2,3-14C]-labelled material were also prepared as described in the preceding paper. The latter substrate was used to establish conditions in which little loss of tritium would occur (found; about 7%) on cleavage to acetyl-CoA in the presence of 3-hydroxyacyl-CoA dehydrogenase and acetyl-CoA acetyltransferase. Little loss of tritium indicates a small degree of racemization of the stereospecifically 2-tritiated 3-hydroxyacyl-CoA derivatives at the level of transiently formed acetoacetyl-CoA and acetyl-CoA. This ensures high optical purity of the chiral acetates generated from the stereospecifically tritiated hydroxybutyryl-CoA specimens listed in paragraph (2). 4. These two acyl-CoA derivatives and the symmetrically tritiated 3S-3-hydroxy[2-3H2]butyryl-CoA listed in paragraph (3) were converted to the acetates enzymically in the sequence hydroxy-butyryl-CoA leads to acetoacetyl-CoA leads to acetyl-CoA leads to acetate. The isolated acetates were assayed for chirality by conversion to the malates and fumarates as usual. 5. The malate formed from 3S-3-hydroxy[2-3H2]butyryl-CoA on incubation with fumarase lost nearly 50%, that derived from 2R,3S-3-hydroxy[2-2H1,3H1]butyryl-CoA (plus 3R-diastereomer) retained about 26% and that derived from 2S,3S-3-hydroxy[2-1H1,3H1]butyryl-CoA retained about 78% of its total tritium content. 6. It was concluded that the detachment of acetyl-CoA from acetoacetyl-CoA on acetyl-CoA acetyltransferase occurs with inversion of configuration at the methylene group which becomes methyl.

Serum and erythocyte argininosuccinate lyase assay by NADH fluorescence generated from formed fumarate

Measurement of argininosuccinase (I; EC 4.3.2.1) activity is useful in following the course of disease in hepatitis and in screening for the genetic defect, argininosuccinic aciduria. Methodology is proposed for a novel procedure for the determination of I in serum and erythrocytes. In the procedure, fumarate, generated in the reaction, is assayed by conversion to malate with fumarase, determining the malate enzymatically with malate dehydrogenase, and estimating the NADH formed spectrofluorometrically. By this procedure, the enzyme activity in serum from normal individuals is less than 11 mumol/liter of erthrocytes/per hour. The correlation coefficient between results by this method and by the colorimetric method, which measures the arginine generated in the reaction, is +0.97 for serum and +0.98 for erythrocytes. The proposed procedure has a relatively low initial blank, requires less serum, and is completed faster.

Synteny of the human loci for fumarate hydratase and udpg pyrophosphorylase with chromosome 1 markers in somatic cell hybrids

The segregation of the loci for 26 human enzyme markers was studied in man-Chinese hamster somatic cell hybrids. The results showed synteny of the human loci for fumarate hydratase, UDPG pyrophosphorylase, phosphogluconate dehydro-genase, phosphoglucomutasei, and peptidase-C (chromosome 1). Furthermore, the synteny of the human loci for mannose phosphate isomerase and the leukocytic form of pyruvate kinase was confirmed.