Clinicopathological, immunological and genetic studies of CD30+ anaplastic large cell lymphoma of B-cell type; association with Epstein-Barr virus in a Japanese population

The clinicopathological features, the immunophenotype, and the presence of Epstein-Barr virus (EBV)-associated genomes and gene products were examined in 17 cases of CD30+ anaplastic large cell lymphoma (ALCL) of B-cell type. Microscopically, the 17 cases were divided into ten cases of the monomorphic type and seven cases of the pleomorphic type. EBV was detected in 6 of 17 cases (38 per cent) by RNA in situ hybridization (ISH) with EBV-encoded RNA (EBER1). EBER1+ cases consisted of two cases (20 per cent) of the monomorphic type and four cases (57 per cent) of the pleomorphic type. The five EBER1+ cases showed clonality of the EBV genome by Southern blotting, consistent with the presence of EBV in a monoclonal proliferation. The EBV-encoded latent membrane protein 1 (LMP1) was found in all six EBER1+ cases and EBV-encoded nuclear antigen 2 (EBNA2) was present in two cases by immunohistochemistry. No expression of LMP1 or EBNA2 was observed in the EBER1-cases. The EBER1+ cases had a tendency for a more favourable prognosis than the EBER1-cases. It is concluded that EBV has an association with CD30+ ALCL of B-cell type in the Japanese population studied, and especially with the large pleomorphic type. EBV infection may play a pathoaetiological role and may influence clinical behaviour.

Chemiluminescence enzyme immunoassay using bacterial magnetic particles

A novel chemiluminescence enzyme immunoassay using bacterial magnetic particles (BMPs) has been developed for highly sensitive and rapid detection of immunoglobulin G. Antibody was immobilized onto BMPs using the heterobifunctional reagents sulfosuccinimidyl 6-[3'-(2-pyridyldithio) propionamido]hexanoate (sulfo-LC-SPDP) and sulfosuccinimidyl 4-(N-maleimidomethyl)cyclohexane-1-carboxylate (sulfo-SMCC). For the highly sensitive immunoassay method using these BMPs, a good relationship was obtained between the luminescence intensity and mouse IgG concentration in the range of 1-10(5) fg/mL. Furthermore, in order to reduce assay time and to simplify operations, a rapid chemiluminescence enzyme immunoassay method has been developed. The rapid method was completed in 10 min. A linear relationship was obtained between the luminescence and mouse IgG concentration in the range of 10-1000 ng/mL.

Arthroscopic posterior cruciate ligament reconstruction using hamstring tendons: one-incision technique with Endobutton

The one-incision surgical technique using autogenous hamstring tendons with Endobutton (Acufex Microsurgical Inc. Mansfield, MA) femoral end fixation for posterior cruciate ligament reconstruction is described. This technique avoids a second incision on the femoral side, and is adaptable to various graft materials (autogenous or allogeneic bone-patellar tendon-bone, hamstring, or Achilles tendon.

Specific detection of deleted mitochondrial DNA by in situ hybridization using a chimera probe

We report a new method for the specific detection of the mutant mitochondrial DNA (mtDNA) that contains the 4977-bp deletion. We designed an oligonucleotide probe that was designated the 'ATP8/ND5 Chimera' probe: its 5'- and 3'-portions correspond to the ATP8 gene and the ND5 gene, respectively, and its middle portion includes the 13-bp direct repeat sequence that flanks the 4977-bp deletion. By Southern blot analysis, this chimeric probe specifically detected the deleted mtDNA, even in the presence of both normal mtDNA and other mtDNA deletions. The specificity of the probe was further confirmed by in situ hybridization of muscle fibers from patients with Kearns-Sayer syndrome who carry the deleted DNA in the heteroplasmic state. The deleted mtDNA was markedly accumulated in cytochrome-c oxidase (COX)-deficient ragged-red fibers. In tissues where multiple deleted mtDNAs were detected, such as muscle tissues from a patient with myotonic dystrophy and from an aged individual, the in situ hybridization detected a small number of muscle fibers that contained the deleted mtDNA. These results indicate that in situ hybridization using this chimera probe is a useful and specific method for detecting a small amount of deleted mtDNA.

Formation of crossline as a fluorescent advanced glycation end product in vitro and in vivo

Crossline is one of the major advanced glycation end products resulting the reaction mixture of free amino group(s) such as epsilon-one in lysine with D-glucose in vitro. To study crossline formation on proteins in vitro and in vivo, polyclonal antiserum to the crossline hapten was prepared. This antiserum reacted with bovine and human serum albumin that had been modified by prolonged incubation with glucose as well as with crossline itself. Antisera did not react with unmodified serum albumin or the other Maillard-related compounds. Crossline was formed in a time-dependent manner when a mixture of six different proteins was incubated with glucose at pH 7.2 or 9.0. Crossline levels could be measured in rat lens proteins and the levels increased with age. The crossline content of lens proteins in diabetic rats was more than two-fold higher than that of age-matched controls. Results of this study suggest that most proteins containing advanced glycation end products have crossline-like structures. Measurement of crossline-like structures in biological specimens may provide an index of aging and of the development of diabetic complications.

Cephalometric comparison of craniofacial morphology between primary bone grafted and nongrafted complete unilateral cleft lip and palate adults

The effect of primary bone grafts on craniofacial growth was evaluated in adult patients with complete unilateral cleft lip and palate (UCLP). The subjects were 18 UCLP patients with primary bone grafts and a control group of 36 UCLP patients without bone grafts. The former received primary transplantation of autogenous rib bone simultaneously with primary cheiloplasty by the same surgeon between 1963 and 1969. Frontal and lateral cephalograms taken after 16 years of age were traced. Skeletal landmarks were identified on them, and their x,y-coordinates were digitized. The effects of gender and/or primary bone graft on the craniofacial morphology were tested by ANOVA using 21 angles, 8 breadths, 13 distances, and 2 ratios. Nasal cavity breadth was wider in the primary bone grafted group. However, the anterior maxilla in that group was more upward and retruded than that in the nongrafted group. The primary bone grafted group was divided into two subgroups based on the overjet of the incisors: group N = normal overjet; group C = anterior cross-bite. There was no difference in the maxilla between groups N and C. However, the mandible in group C was more anterior and superior than in group N. In conclusion, primary bone graft may impede maxillary horizontal and vertical growth to a certain degree, and severe anterior cross-bite in primary bone grafted subjects may be brought about by mandibular closure.

[A 63 year-old man with progressive gait disturbance and dysarthria]

We report a 63-year-old man with progressive gait disturbance and dysarthria. The patient was apparently well until the age of 62 (February, 1990) when he noted unsteadiness of gait. Two months later, dysarthria appeared. He was admitted to Juntendo Izunagaoka Hospital on April 23, 1990. Neurologic examination revealed a mentally sound man with normal higher cerebral functions. Cranial nerves were unremarkable except for scanning speech. His gait was ataxic with positive Romberg sign. No motor weakness was noted, however, he had hypotonia and cerebellar ataxia. Deep tendon reflexes were retained and the plantar response was flexor. Pain, touch and vibration senses were diminished in the distal parts of the lower extremities. Laboratory examination revealed a 2.5 cm mass in the left lung field. Cranial MRI revealed a small T1-low and T2-high signal intensity lesion in the left temporal lobe. Abdominal CT scan revealed multiple low density lesions in the liver. His subsequent course was complicated by progressive deterioration in his gait and loss of deep tendon reflexes. He expired on November 24, 1990. The patient was discussed in the neurological CPC and the chief discussant arrived at the conclusion that the patient had anti-Hu associated paraneoplastic encephalomyelitis and sensory neuropathy. Some other participants thought that the patient had carcinomatous cerebellar degeneration. Postmortem examination revealed a 4x4 cm mass lesion involving the left S4-S5 segments. Histologic examination of the tumor was small cell carcinoma. Many metastatic foci were found in the liver. The cerebral hemispheres were unremarkable except for a small wedge-shaped tissue defect in the left temporal lobe which appeared to have been caused by old head trauma which the patient had received. The cerebellar vermis showed slight enlargement of cortical sulci, however, the cerebellar hemispheres appeared unremarkable. Upon histologic examination, marked loss of Purkinje cells was noted, particularly in the cerebellar anterior lobe. The dentate nucleus showed slight cell loss with increase in fat granule cells. The inferior olive was normal. The histologic characteristics were consistent with the pathologic diagnosis of carcinomatous cerebellar degeneration. No evidence of limbic encephalitis was seen. The peripheral nerve was not examined.

PIG-B, a membrane protein of the endoplasmic reticulum with a large lumenal domain, is involved in transferring the third mannose of the GPI anchor

Many eukaryotic cell surface proteins are bound to the membrane via the glycosylphosphatidylinositol (GPI) anchor that is covalently linked to their carboxy-terminus. The GPI anchor precursor is synthesized in the endoplasmic reticulum (ER) and post-translationally linked to protein. We cloned a human gene termed PIG-B (phosphatidylinositol glycan of complementation class B) that is involved in transferring the third mannose. PIG-B encodes a 554 amino acid, ER transmembrane protein with an amino-terminal portion of approximately 60 amino acids on the cytoplasmic side and a large carboxy-terminal portion of 470 amino acids within the ER lumen. A mutant PIG-B lacking the cytoplasmic portion remains active, indicating that the functional site of PIG-B resides on the lumenal side of the ER membrane. The PIG-B gene was localized to chromosome 15 at q21-q22. This autosomal location would explain why PIG-B is not involved in the defective GPI anchor synthesis in paroxysmal nocturnal hemoglobinuria, which is always caused by a somatic mutation of the X-linked PIG-A gene.

An epidermal growth factor receptor/Jak2 tyrosine kinase domain chimera induces tyrosine phosphorylation of Stat5 and transduces a growth signal in hematopoietic cells

The Jak family of tyrosine kinases and the Stat family of transcription factors have been implicated in transducing signals from the hematopoietic growth factor receptors. To explore the role played by a member of the Jak family, Jak2, in hematopoietic cell growth signaling, we constructed a chimeric cDNA coding for the Jak2 tyrosine kinase domain linked to the extracellular and transmembrane regions of the epidermal growth factor (EGF) receptor (EGFR) and expressed the chimera in an interleukin (IL)-3-dependent cell line, 32D. When deprived of IL-3, EGF prevented apoptosis of the transfected cells, induced dose-dependent proliferation, and supported long-term growth. EGF stimulation of the transfectants induced dose-dependent tyrosine phosphorylation of the EGFR/Jak2 chimera and Stat5, which correlated with the EGF dose dependence of cell proliferation. On the other hand, EGF did not induce tyrosine phosphorylation of other factors implicated in cytokine receptor signaling, including the IL-3 receptor beta subunit, Jak kinases, Stat proteins other than Stat5, Shc, Syp, and mitogen-activated protein kinases. These results suggest that the activation of Jak2 may be sufficient for transducing a growth signal in hematopoietic cells by activating the Stat5 pathway or previously unidentified signaling pathways. In addition, because EGF induces homodimerization of the EGFR to activate its tyrosine kinase activity, the present study, which shows EGF-dependent activation of the EGFR/Jak2 chimera, implies that Jak2 may also become activated by homodimerization.

Human calcitonin has the same inhibitory effect on osteoclastic bone resorption by human giant cell tumor cells as salmon calcitonin

Human calcitonin (hCT) has been reported to have a less hypocalcemizing effect on rats and to have a lower binding affinity for the receptor of mouse osteoclasts than salmon CT(sCT). In this study we comparatively examined the effect of hCT and sCT on osteoclastic bone-resorbing activity of unfractionated cells obtained from human giant cell tumor of bone and from rabbit and mouse long bones. We found that hCT had the same inhibitory effect as sCT on the bone-resorbing activity of human and rabbit osteoclastic cells, but a different one on that of mouse cells. These results indicate that the activity of drugs should be assayed using human cells if possible.

Suppression of inducible nitric oxide synthase mRNA expression by tryptoquinone A

Triptoquinone A (TQA), which is an anti-inflammatory constituent in plants, was studied for its suppressive effect on nitric oxide production by LPS. TQA significantly suppressed smooth muscle relaxation and increase in cyclic GMP levels by nitric oxide (NO) in an L-arginine-induced relaxation experiment. The mechanistic studies showed that TQA did not directly inhibit NO radicals and inducible nitric oxide synthase (iNOS) enzyme but suppressed IL-1 beta and iNOS mRNA expression by LPS. The suppression level of iNOS gene expression by TQA was comparable to that by dexamethasone. TQA may be a useful candidate for the development of a drug as a potent inhibitor of iNOS gene over-expression.

Uterine leiomyosarcoma metastasis to the skull--case report

A 54-year-old female presented with a rare uterine leiomyosarcoma metastasis to the skull appearing as a gross mass beneath her scalp. She had no neurological or other physical symptoms on admission. Computed tomography and magnetic resonance imaging demonstrated an enhanced dumbbell-shaped mass at the mid-frontal region beneath the scalp. The tumor was totally removed with normal surrounding bone and dura. The histological diagnosis was leiomyosarcoma. Her postoperative course was uneventful, and she received adjuvant chemotherapy. However, multiple distant bone metastases developed 1 year later. Immediate and radical resection of such tumors is recommended.

Somatic cell mutations at the glycophorin A locus in erythrocytes of atomic bomb survivors: implications for radiation carcinogenesis

To clarify the relationship between somatic cell mutations and radiation exposure, the frequency of hemizygous mutant erythrocytes at the glycophorin A (GPA) locus was measured by flow cytometry for 1,226 heterozygous atomic bomb (A-bomb) survivors in Hiroshima and Nagasaki. For statistical analysis, both GPA mutant frequency and radiation dose were log-transformed to normalize skewed distributions of these variables. The GPA mutant frequency increased slightly but significantly with age at testing and with the number of cigarettes smoked. Also, mutant frequency was significantly higher in males than in females even with adjustment for smoking and was higher in Hiroshima than in Nagasaki. These characteristics of background GPA mutant frequency are qualitatively similar to those of background solid cancer incidence or mortality obtained from previous epidemiological studies of survivors. An analysis of the mutant frequency dose response using a descriptive model showed that the doubling dose is about 1.20 Sv [95% confidence interval (CI): 0.95-1.56], whereas the minimum dose for detecting a significant increase in mutant frequency is about 0.24 Sv (95% CI: 0.041-0.51). No significant effects of sex, city or age at the time of exposure on the dose response were detected. Interestingly, the doubling dose of the GPA mutant frequency was similar to that of solid cancer incidence in A-bomb survivors. This observation is in line with the hypothesis that radiation-induced somatic cell mutations are the major cause of excess cancer risk after radiation exposure. Furthermore, the dose response was significantly higher in persons previously or subsequently diagnosed with cancer than in cancer-free individuals. This may suggest an earlier onset of cancer due to elevated mutant frequency or a higher radiation sensitivity in the cancer group, although the possibility of dosimetry errors should be considered. The findings obtained in the present study suggest that the GPA mutant frequency may reflect the cancer risk among people exposed to radiation.

Inducible osteonecrosis in a rabbit serum sickness model: deposition of immune complexes in bone marrow

We established inducible osteonecrosis in a rabbit serum sickness model. Osteonecrosis with marrow necrosis could be induced by the intravenous injection of horse serum in two doses separated in time by a period of three weeks. In this model, osteonecrosis could be successfully produced in rabbit femoral metaphysis. The incidence of marrow necrosis was 45% (9 of 20 rabbits) and trabecular necrosis occurred in 6 of 20 rabbits (30%) at 7 days after the second injection of the horse serum. In bone marrow of the femoral metaphysis, extravasation of erythrocytes and the formation of micro-thrombi in arterioles were often observed in an early stage of the present model and both findings correlate well each other (p = 0.0001). Immune complexes could be demonstrated using immunohistochemistry in bone marrow of the femoral metaphysis as well as in glomeruli of the kidney. Extravasation of erythrocytes in bone marrow of the femoral metaphysis was observed in 8 of 12 (67%) cases with immune complex deposition in the sinusoidal space of the femoral metaphysis and in 12 of 21 (57%) cases with immune complex deposition in glomeruli of the kidney. Immune complex deposition both in the sinusoidal space of femoral bone marrow (p = 0.0385) and in glomeruli of the kidney (p = 0.0209) closely related to extravasation of erythrocytes and microthrombi in arterioles in the early stage of this model. Early microcirculatory injury (extravasation of erythrocytes and microthrombi in arterioles) adjacent to osteonecrosis could be induced by immune complex deposition in femoral bone marrow and might be predictable characteristics for the inducible osteonecrosis in the present serum sickness model. The important findings in this study were that early microcirculatory injury was closely related to the deposition of immune complexes in femoral bone marrow, and that early microcirculatory injury associated with immune complex deposition was located close to osteonecrotic regions.

[Coronary arterial bypass grafting for angina pectoris suspected with aortitis syndrome: a case report]

We report herein the case of a 56-year-old man with angina pectoris suspected to be accompanied with aortitis syndrome who underwent coronary artery bypass grafting (CABG). His cerebral blood flow consisted of only that of the right vertebralartery, and the marked collaterals of the bronchial artery anastomosing to the coronary artery. CABG was performed under combined with electrical fibrillation and systemic deep hypothermia, for fear of a bad influence on the cerebral tissue by the influx of high potassium cardioplegic solution. The postoperative course was uneventful and the coronary angiography revealed that the all graft were patent.

[Open heart surgery in patients with chronic dialysis]

From January, 1986 to May, 1995, twelve patients with dialysis (11 hemodialysis; HD, and one continuous ambulatory peritoneal dialysis; CAPD) received open heart surgery. They consist of 10 males and two females aged between 35 and 66 with a mean of 58.8. The duration of dialysis was 6.8 years in a mean (the shortest for 2 months and the longest for 16 years). They classified into an equal number of four in NYHA class II, III and IV. Two of them had isolated coronary artery bypass grafting, four had aortic valve replacement (AVR) and two had mitral valve replacement (MVR). Others were each one of AVR and MVR, AVR plus MVR with tricuspid annuloplasty (TAP), AVR plus TAP, and removal of left atrial myxoma. All patients except for one of CAPD were dialysed daily 2 or 3 days before operation. Three patients were managed postoperatively with HD, one with PD, six with continuous hemodiafiltration, and two with continuous hemofiltration. The operative mortality was 25% (3/12). The causes of death were left ventricular rupture, bronchospasm, and respiratory failure. All patients who died were in class in III and IV. For the improvement of the results we emphasize the necessity of early operation that should be scheduled in class II period.

Immunoexpression of the alpha subunit of a guanine nucleotide-binding protein (Go) in pulmonary neuroendocrine cells and neoplasms

The alpha subunit of a GTP-binding protein, Go, was investigated in pulmonary neuroendocrine neoplasms and fetal tissues of the lung by an immunohistochemical method. Positive immunostaining for the alpha subunit of Go (Go alpha) was found predominantly on the cell membrane and found occasionally in the cytoplasm. Typical carcinoids were all positively stained (9/9), and small cell carcinoma showed weaker and less frequent staining (5 positive cases in 10). Atypical carcinoids were variously stained (3/4). The tendency for obvious neuroendocrine differentiation to be immunohistochemically determined in typical carcinoids and not in small cell carcinoma is also true of staining for neuron specific enolase (NSE), chromogranin A (CG-A) and synaptophysin. In the lung, Go alpha-immunostaining was positive not only in nerve tissues but also in the airway epithelium. In the fetal lung, serial sections immunostained for NSE, CG-A and Go alpha confirmed that Go alpha-immunoreactive cells belong to the neuroendocrine cell population. The biological significance of Go alpha is unclear in normal and neoplastic lung tissues, but Go alpha is a useful marker of neuroendocrine cells and neoplasma of the lung.

Testis-specific expression of mRNAs for a unique human type 1 hexokinase lacking the porin-binding domain

Several enzymes in the glycolytic pathway are reported to have spermatogenic cell-specific isozymes. We reported recently the cloning of cDNAs representing three unique type 1 hexokinase mRNAs (mHk1-sa, mHk1-sb, and mHk1-sc) present only in mouse spermatogenic cells and the patterns of expression of these mRNAs (Mori et al., 1993: Biol Reprod 49:191-203). The mRNAs contain a spermatogenic cell-specific sequence, but lack the sequence for the porin-binding domain that somatic cell hexokinases use to bind to a pore-forming protein in the outer mitochondrial membrane. We now report the cloning of cDNAs representing three unique human type 1 hexokinase mRNAs (hHK1-ta, hHK1-tb, and hHK1-tc) expressed in testis, but not detected by Northern analysis in other human tissues. These mRNAs also contain a testis-specific sequence not present in somatic cell type 1 hexokinase, but lack the sequence for the porin-binding domain. The hHK1-tb and hHK1-tc mRNAs each contain an additional unique sequence. The testis-specific sequence of the human mRNAs is similar to the spermatogenic cell-specific sequence of the mouse mRNAs. Furthermore, Northern analysis of RNA from mouse, hamster, guinea pig, rabbit, ram, human, and rat demonstrated expression of type 1 hexokinase mRNAs lacking the porin-binding domain in the testes of these mammals. These results suggest that hexokinase may have unique structural or functional features in spermatogenic cells and support a model proposed by others for hexokinase gene evolution in mammals.

Atypical adenomatous hyperplasia and bronchoalveolar lung carcinoma. Analysis by morphometry and the expressions of p53 and carcinoembryonic antigen

Atypical adenomatous hyperplasia (AAH) of the lung is a putative precursor of bronchoalveolar carcinoma (BAC). To define the steps in its development and to clarify at which stage critical cellular events occur, we studied 65 lesions of AAH, early BAC, and overt BAC by morphometric analysis and immunohistochemical evaluation of expression of p53 protein and carcinoembryonic antigen (CEA). Both the nuclear area and lesion size increased from AAH to early BAC and to overt BAC; the standardized variation of nuclear area was smallest in overt BAC. Discriminant analysis using these morphometric parameters revealed high accuracy rates for the respective categories. Analysis of distribution of lung lesions in terms of nuclear area and lesion size yielded effective, potentially diagnostic cutoff values for distinction between AAH and early BAC. Both p53 and CEA expression tended to increase with the advance of atypia grade. In particular, high-level p53 expression was strongly correlated with overt BAC. These findings indicate that our classification of lung lesions is reproducible and thus useful for analyzing the development of BAC. Furthermore, some kinds of p53 gene abnormalities that are correlated with high-level p53 expression likely play an important role in the progression of early to overt BAC.

Targeted gene disruption of Hsp70-2 results in failed meiosis, germ cell apoptosis, and male infertility

In addition to the five 70-kDa heat shock proteins (HSP70) common to germ cells and somatic tissues of mammals, spermatogenic cells synthesize HSP70-2 during meiosis. To determine if this unique stress protein has a critical role in meiosis, we used gene-targeting techniques to disrupt Hsp70-2 in mice. Male mice homozygous for the mutant allele (Hsp70-2 -/-) did not synthesize HSP70-2, lacked postmeiotic spermatids and mature sperm, and were infertile. However, neither meiosis nor fertility was affected in female Hsp70-2 -/- mice. We previously found that HSP70-2 is associated with synaptonemal complexes in the nucleus of meiotic spermatocytes from mice and hamsters. While synaptonemal complexes assembled in Hsp70-2 -/- spermatocytes, structural abnormalities became apparent in these cells by late prophase, and development rarely progressed to the meiotic divisions. Furthermore, analysis of nuclei and genomic DNA indicated that the failure of meiosis in Hsp70-2 -/- mice was coincident with a dramatic increase in spermatocyte apoptosis. These results suggest that HSP70-2 participates in synaptonemal complex function during meiosis in male germ cells and is linked to mechanisms that inhibit apoptosis.

Electrostatic environment of the tryptophylquinone cofactor in methylamine dehydrogenase: evidence from resonance Raman spectroscopy of model compounds

Methylamine dehydrogenase (MADH) utilizes its endogenous tryptophan tryptophylquinone (TTQ) as a cofactor in enzymatic catalysis, with the C6 carbonyl of the quinone implicated as the site of attack by substrates and other nucleophiles. Resonance Raman (RR) spectroscopy provides an ideal method for investigating the state of this carbonyl group whose C==O stretch is distinct from other vibrational modes of the cofactor and is readily identified by its shift to lower energy in H218O. In a series of indole 6,7-quinone models for TTQ, the in-phase stretching vibration of the two C==O groups occurs at 1650 cm-1 in nonpolar solvents and shifts to 1638 cm-1 in H2O. The absorption maximum undergoes an analogous shift from 400 to 425 mm. The spectral properties of the indole quinones in H2O approach the corresponding values in Thiobacillus versutus MADH (C==O stretch at 1612 cm-1, lamdamax at 440mm) and are indicative of strongly hydrogen bonding of the C==O and NH groups of the cofactor in the native enzyme. Addition of monovalent cations [NH4+,Cs+, and (CH3)3NH+] to MADH causes further increases in the lamdamax and decreases in the frequency of the C==O stretch[1590 cm-1 with (CH3)3NH+]. This implies a strong electrostatic interaction between monovalent cations and a carbonyl oxygen (most likely at C6) in TTQ. The fact that these cations behave as competitive inhibitors of the methylamine substrate suggests that methylamine binds to the same location in the enzyme prior to its covalent reaction with the cofactor. Addition of monovalent cations to the one-electron-reduced semiquinone form MADH results in RR spectral shifts for a number of vibrational modes of the cofactor. Thus, the ability of monovalent cations to promote and stabilize the formation of the semiquinone intermediate is also due to their direct electrostatic interaction with the TTQ cofactor.