Upper Thoracic Compensation against Global Malalignment and Spinopelvic Mismatch in Adult Spinal Deformity Patients Analyzed Using the EOS Imaging System.

Introduction: Patients with adult spinal deformity (ASD) develop compensatory mechanisms. The Cobb angle between T4 and T12 has been used as a standard to define thoracic kyphosis (TK) because radiological evaluation is difficult in upper thoracic region. The upper thoracic compensatory mechanism has not been sufficiently explored, and focal thoracic compensation remains poorly understood. This study aimed to determine upper sagittal thoracic compensation and features of thoracic compensation in ASD patients. Methods: The records of 218 consecutive patients who underwent full-standing EOS imaging were retrospectively examined. Spinopelvic parameters-including the T1-T12, T4-T12, T1-T4, T5-T8, and T9-T12 angles-were measured using a dedicated and validated software. The relationship between the thoracic and spinopelvic parameters was statistically evaluated. Thoracic compensation was compared among four typical types of spinal deformity. Results: A total of 127 ASD patients met the inclusion criteria. TK(1-12) was negatively correlated with the sagittal vertical axis (SVA) (r=-0.35), T1 pelvic angle (TPA) (r=-0.29), and pelvic incidence minus lumbar lordosis (PI-LL) (r=-0.60). TK(1-4) showed a stronger correlation with the SVA and TPA than TK(5-8) or TK(9-12) (r=-0.39, -0.38, respectively). TK(1-4), TK(5-8), and TK(9-12) had a similar negative correlation with PI-LL; however, TK(5-8) had the strongest correlation (r=-0.38). Both age and TK(9-12) were significantly associated with decreased TK(1-4), and vertebral fracture was significantly associated with increased TK(9-12). Both patients with high SVA and those in the hyperthoracic kyphosis group had lower TK(1-4) angles. Conclusions: In ASD patients, upper thoracic spine compensation plays an important role in countering global malalignment. The middle part of the thoracic spine has a strong correlation with LL. This study findings can help clinicians better manage ASD patients.

Micro-/macroscopic and density functional studies of the interactions between molybdenum trioxide and C60 molecule.

We have investigated the interactions between C60 and (MoO3)n using scanning tunneling microscopy with spectroscopy (STM/STS) and ex situ ultraviolet-visible-near-infrared (UV-vis-NIR) spectroscopy in combination with density functional theory (DFT) calculations. The formation of (MoO3)n chemically bound to C60 is energetically favorable due to ΔG < 0 for n = 1, 2, 4, 6, 8, and 9, and they well reproduced the histogram of the height of (MoO3)n on the C60 (111) terrace obtained by a STM height-profile. STS results demonstrated the upward energy shift of both highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of C60 in the vicinity of (MoO3)n (n = 6 or 9), which is consistent with the previous results of the co-deposited C60/MoO3 film obtained using photoemission and inverse photoemission spectroscopy [Wang and Gao, Appl. Phys. Lett. 105, 111601 (2014), Yang et al., J. Phys.: Condens. Matter 28, 185502 (2016), and Li et al., J. Phys. Chem. C 118, 4869 (2014)]. Theoretical calculations of (MoO3)n (n = 1, 2, 4, 6, 8, and 9) chemically bound to C60 indicated that 0.01-0.32 holes are injected into C60 by (MoO3)n nanoclusters, and UV-vis-NIR and DFT results found that the hole doping to C60 is caused via the electron transfer from the HOMO of C60 to the LUMO of (MoO3)n. Furthermore, it is noted that the C60-(MoO3)n interactions exhibit a high heat resistance up to 250 °C by examining the UV-vis-NIR spectra of a co-deposited C60/MoO3 (6:4) film before and after thermal annealing. The present findings provide useful information for the practical use of P-type C60-based thermoelectric devices.

Relationship Between Sacroiliac Joint-related Pain and Spinopelvic Mobility.

STUDY DESIGN: A case-control study. OBJECTIVE: To evaluate the relationship between sacroiliac joint-related pain (SIJ-RP) and spinopelvic mobility. SUMMARY OF BACKGROUND DATA: No specific radiological findings are available for the diagnosis of SIJ-RP. A previous study reported that a higher pelvic incidence and sacral slope (SS) values were significantly associated with sacroiliac joint pain. The concept of spinopelvic mobility, which is evaluated by the differences between SS in the standing and sitting positions, has been the focus of hip and spine surgeries in recent years. MATERIALS AND METHODS: The SIJ-RP group comprised patients diagnosed with SIJ-RP based on physical findings and their response to analgesic injections. No other lumbar or hip joint diseases were observed. The non-SIJ-RP group comprised patients with lower back pain for reasons other than SIJ-RP. Radiographs of the lateral view of the pelvis in the standing and sitting positions were evaluated for all patients. We compared and analyzed the backgrounds, SS in the two positions, and difference in SS between the two positions in both groups. RESULTS: In total, 245 patients were included in the study, with 49 and 196 patients in the SIJ-RP and non-SIJ-RP groups, respectively. More female patients experienced SIJ-RP than male patients ( P =0.0361). There were significant differences between the groups for SS in standing ( P =0.0076), sitting ( P =0.0005), and those with a difference between sitting and standing of <5° ( P =0.0278) in the univariate analyses. Logistic regression analyses, after adjustment for age and sex, revealed significant differences between the groups with an SS difference <5° ( P =0.0088; 95% confidence interval, 1.280-5.519), with an odds ratio of 2.7. CONCLUSION: On evaluating spinopelvic mobility, we found that SIJ-RP was related to hypomobility of the sacrum, which could indicate the hypermobility of the sacroiliac joint.

Metastatic intradural extramedullary spinal cord tumor from ovarian cancer: A case report with a literature review.

Context: Metastatic intradural extramedullary spinal cord tumors are extremely rare.Findings: A 76-year-old woman presented with intractable neck pain. Three years earlier, she had been treated for ovarian cancer with bilateral salpingo-oophorectomy. A year later, she underwent resection of a brain metastasis. Magnetic resonance imaging (MRI) showed an encapsulated intradural extramedullary mass at C4-C5. C4-C5 hemilaminectomy, tumor resection, and biopsy were performed. Histological examination of the resection revealed an adenocarcinoma. After surgery, her intolerable neck-shoulder pain was fully resolved, and she had no difficulties with daily living activities. However, two months later, she underwent gamma knife radiosurgery for the recurrent metastatic brain tumor, and four months later, she died from cachexia.Conclusion: Although cases of metastatic intradural extramedullary spinal tumors from ovarian cancer are extremely rare, their possibility should be considered in the differential diagnosis. A history of brain metastases and enhancement on T1-weighted MRI were helpful for making an accurate diagnosis.

Impact of focal apex angle on postoperative decompression status of the spinal cord and neurological recovery after cervical laminoplasty.

OBJECTIVE: Although anterior compression factors and cervical alignment affect neural decompression, cervical laminoplasty may be used to achieve indirect posterior decompression. The focal apex (FA) angle of the anterior compression factor of the spine represents the degree of anterior prominence toward the spinal cord. The authors investigated the mechanism underlying the influence of FA angle and cervical alignment on spinal cord alignment (SCA) after laminoplasty, including how high-intensity signal cord change (HISCC) on preoperative T2-weighted MRI (T2-MRI) may affect neurological improvement. METHODS: We performed a retrospective study of patients who underwent laminoplasty for CSM or OPLL at two hospitals (Kanto Rosai Hospital, Kawasaki City, and Yokohama Minami Kyousai Hospital, Yokohama City, Japan) between April 2004 and March 2015. In total, 109 patients (mean age 67.3 years) with cervical compression myelopathy were included. FA angle was defined as the preoperative angle between the lines from the top of the prominence to the upper and lower adjacent vertebrae. Preoperative cervical alignment was measured between the C2 and C7 vertebrae (C2-7 angle). MRI was used to classify SCA as lordosis (type-L SCA), straight (type-S), local kyphosis (type-LK), or kyphosis (type-K). Preoperative HISCC was investigated by using T2-MRI. Neurological status was evaluated by using the Japanese Orthopaedic Association score. RESULTS: The mean preoperative FA and C2-7 angles were 32.1° and 12.4°, respectively. Preoperative SCA was type-L or type-S in 53 patients. The neurological recovery rate (NRR) was significantly higher for patients with preoperative type-L and type-S SCA (51.4% for those with type-L and 45.0% for those with type-S) than for patients with other types (35.3% for those with type-LK and 31.7% for those with type-K). Among patients with preoperative type-L or type-S SCA, 87.3% maintained SCA; however, 5/12 (41.7%) patients with a preoperative average C2-7 angle < 12.4° and an average FA angle > 32.1° had postoperative type-LK or type-K SCA. SCA changed to type-L or type-S in 13.0% of patients with preoperative type-LK or type-K SCA. Moreover, in these patients, FA angle was significantly smaller and NRR was significantly higher than in other patients in whom postoperative SCA remained type-LK or type-K. Preoperative T2-MRI showed 73 patients with HISCC (43 with type-L and type-S, and 30 with type-LK and type-K SCA) and 36 without HISCC (20 with type-L and type-S, and 16 with type-LK and type-K SCA); the NRRs of these patients were 42.6% and 41.2%, respectively. No significant differences in SCA or NRR were observed between patients with and without HISCC. CONCLUSIONS: NRR depends on preoperative SCA type; however, it is possible to change the type of SCA after laminoplasty. Preoperative FA and C2-7 angles influence change in SCA; therefore, they are important parameters for successful decompression with cervical laminoplasty.

Characteristics of the spinopelvic parameters of patients with sacroiliac joint pain.

To evaluate the characteristics of the spinopelvic parameters on radiography in patients with sacroiliac joint pain (SIJP). Two hundred fifty patients were included and divided into the SIJP group (those diagnosed with SIJP based on physical findings and response to analgesic periarticular injections; n = 53) and the non-SIJP group (those with low back pain [LBP] because of other reasons; n = 197). We compared their demographic characteristics and spinopelvic parameters using radiography. All differences found in the patients' demographic characteristics and spinopelvic parameters were analyzed. More female participants experienced SIJP than male participants (P = 0.0179). Univariate analyses revealed significant differences in pelvic incidence (PI) (P = 0.0122), sacral slope (SS) (P = 0.0034), and lumbar lordosis (LL) (P = 0.0078) between the groups. The detection powers for PI, SS, and LL were 0.71, 0.84, and 0.66, respectively. Logistic regression analyses, after adjustment for age and sex, revealed significant differences in PI (P = 0.0308) and SS (P = 0.0153) between the groups, with odds ratios of 1.03 and 1.05, respectively. More female participants experienced SIJP than male participants. Higher PI and SS values were related to SIJP among LBP patients.

Influence of comorbid knee osteoarthritis on surgical outcome and sagittal spinopelvic/lower-extremity alignment in elderly patients with degenerative lumbar spondylolisthesis undergoing transforaminal lumbar interbody fusion.

OBJECTIVE: This retrospective study aimed to clarify the influence of comorbid severe knee osteoarthritis (KOA) on surgical outcome in terms of sagittal spinopelvic/lower-extremity alignment in elderly patients with degenerative lumbar spondylolisthesis (DLS). METHODS: In total, 110 patients aged at least 65 years (27 men, 83 women; mean age 74.0 years) who underwent short-segment lumbar fusion were included in the present study. Using the Kellgren-Lawrence (KL) grading system, patients were categorized into those with no to mild KOA (the mild-OA group: KL grades 0-2), moderate KOA (moderate-OA group: KL grade 3), or severe KOA (severe-OA group: KL grade 4). Surgical results were assessed using the Japanese Orthopaedic Association (JOA) scoring system, and spinopelvic/lower-extremity parameters were compared among the 3 groups. Adjacent-segment disease (ASD) was assessed over a mean follow-up period of 4.7 years (range 2-8.1 years). RESULTS: The study cohort was split into the mild-OA group (42 patients), the moderate-OA group (28 patients), and the severe-OA group (40 patients). The severe-OA group contained significantly more women (p = 0.037) and patients with double-level listhesis (p = 0.012) compared with the other groups. No significant differences were found in mean postoperative JOA scores or recovery rate among the 3 groups. The mean postoperative JOA subscore for restriction of activities of daily living was only significantly lower in the severe-OA group compared with the other groups (p = 0.010). The severe-OA group exhibited significantly greater pelvic incidence, pelvic tilt, and knee flexion angle (KFA), along with a smaller degree of lumbar lordosis than the mild-OA group both pre- and postoperatively (all p < 0.05). Overall, the rate of radiographic ASD was observed to be higher in the severe-OA group than in the mild-OA group (p = 0.015). Patients with ASD in the severe-OA group exhibited significantly greater pelvic tilt, pre- and postoperatively, along with less lumbar lordosis, than the patients without ASD postoperatively (all p < 0.05). CONCLUSIONS: A lack of lumbar lordosis caused by double-level listhesis and knee flexion contracture compensated for by far greater pelvic retroversion is experienced by elderly patients with DLS and severe KOA. Therefore, corrective lumbar surgery and knee arthroplasty may be considered to improve sagittal alignment, which may contribute to the prevention of ASD, resulting in favorable long-term surgical outcomes.

Surgical Intervention for Osteoporotic Vertebral Burst Fractures in Middle-low Lumbar Spine with Special Reference to Postoperative Complications Affecting Surgical Outcomes.

The purpose of this study was to investigate the clinical and radiological features of osteoporotic burst fractures affecting levels below the second lumbar (middle-low lumbar) vertebrae, and to clarify the appropriate surgical procedure to avoid postoperative complications. Thirty-eight consecutive patients (nine male, 29 female; mean age: 74.8 years; range: 60-86 years) with burst fractures affecting the middle-low lumbar vertebrae who underwent posterior-instrumented fusion were included. Using the Magerl classification system, these fractures were classified into three types: 16 patients with superior incomplete burst fracture (superior-type), 11 patients with inferior incomplete burst fracture (inferior-type) and 11 patients with complete burst fracture (complete-type). The clinical features were investigated for each type, and postoperative complications such as postoperative vertebral collapse (PVC) and instrumentation failure were assessed after a mean follow-up period of 3.1 years (range: 1-8.1 years). All patients suffered from severe leg pain by radiculopathy, except one with superior-type fracture who exhibited cauda equina syndrome. Nineteen of 27 patients with superior- or inferior-type fracture were found to have spondylolisthesis due to segmental instability. Although postoperative neurological status improved significantly, lumbar lordosis and segmental lordosis at the fused level deteriorated from the postoperative period to the final follow-up due to postoperative complications caused mainly by PVC (29%) and instrument failure (37%). Posterior-instrumented fusion led to a good clinical outcome; however, a higher incidence of postoperative complications due to bone fragility was inevitable. Therefore, short-segment instrument and fusion with some augumentation techniqus, together with strong osteoporotic medications may be required to avoid such complications.

Spondylolysis repair using a pedicle screw hook or claw-hook system. -a comparison of bone fusion rates.

INTRODUCTION: To assess the bone fusion rates and clinical results of two surgical methods (pedicle screw claw-hook fixation and pedicle screw hook fixation) of lumbar spondylolysis repair. METHODS: A multicenter database of surgical patients with lumbar spondylolysis was reviewed. All patients < 20 years old with a minimum of 6 months of follow-up and computed tomography images were included. Operation time and blood loss amount were investigated. Visual analogue scale (VAS; 0-10) scores for lower back pain were evaluated to assess clinical results. RESULTS: A total of 17 patients met the inclusion criteria. Pedicle screw hook fixation was performed in five patients (the hook group), and pedicle screw claw-hook fixation was performed in 13 patients (the claw-hook group). One patient was included in both groups because each method was performed at different lumbar levels (L4 and L5). The bone fusion rates at 3, 6, and 9 months after surgery were significantly higher in the claw-hook group than those in the hook group. Operation time and blood loss amount were not significantly different between the groups. VAS scores improved in the claw-hook group but not in the hook group because of a small number of patients. CONCLUSIONS: Pedicle screw claw-hook fixation was more effective than pedicle screw hook fixation in terms of bone fusion rates.

Retraction Note: Relationship between bone density and bone metabolism in adolescent idiopathic scoliosis.

[This retracts the article DOI: 10.1186/s13013-015-0043-x.].

Relationship between bone density and bone metabolism in adolescent idiopathic scoliosis.

Several authors have confirmed that 27 to 38 % of AIS patients had osteopenia. But few studies have assessed bone metabolism in AIS. This study assessed bone mineral density and bone metabolism in AIS patients using the bone metabolism markers, BAP and TRAP5b. The subjects were 49 consecutive adolescent AIS patients seen at our institutes between March 2012 and September 2013. Sixty-five percent of AIS patients had osteopenia or osteoporosis and 59 % of AIS patients had high values for TRAP5b. The AIS patients with high values of TRAP5b had lower Z scores than those with normal values of TRAP5b. Higher rates of bone resorption are associated with low bone density in AIS patients.

Relationship between bone density and bone metabolism in adolescent idiopathic scoliosis.

Several authors have confirmed that 27 to 38% of AIS patients had osteopenia. But few studies have assessed bone metabolism in AIS. This study assessed bone mineral density and bone metabolism in AIS patients using the bone metabolism markers, BAP and TRAP5b. The subjects were 49 consecutive adolescent AIS patients seen at our institutes between March 2012 and September 2013. Sixty-five percent of AIS patients had osteopenia or osteoporosis and 59% of AIS patients had high values for TRAP5b. The AIS patients with high values of TRAP5b had lower Z scores than those with normal values of TRAP5b. Higher rates of bone resorption are associated with low bone density in AIS patients.

Surgical Treatment of Gorham's Disease with Massive Osteolysis of the Skull and Cervical Spine: A Case Report and Review of Literature.

Gorham's disease is a rare disorder of unknown etiology and variable clinical presentation and is characterized by the proliferation of lymphatic vessels associated with massive regional osteolysis. Although 10 cases involving the skull and cervical spine have been reported in the literature, little is available concerning the surgical treatment of either atlantoaxial dislocation or basilar impression. Most cases have experienced universally unsuccessful treatment with bone grafts, which have led to dissolution. This case report describes the clinical course, and radiotherapeutic, medical, and surgical treatment for Gorham's disease with basilar impression and massive osteolysis of the skull and upper cervical spine. The case of a 27-year-old man with progressive massive osteolysis of the skull and cervical spine is reported. Multiple surgical treatments to decompress the spinal cord and stabilize the skull and upper cervical spine with autologous fibular grafts were performed in order to prevent the progression of atlantoaxial dislocation and basilar impression. Pathologically, radiotherapy failed to show any effect. The efficacy of antiresorptive therapy with bisphosphonates could not be confirmed either clinically or radiologically. Although solid bone fusion was not obtained, the patient has achieved a satisfactory functional outcome and remains completely active after repeated surgeries. Surgical treatment is extremely difficult in cases of Gorham's disease involving the skull and upper cervical spine. Fibular bone grafts seem to show resistance to erosion to osteolytic tissue.

[Differentiation between a thoracic spinal intramedullary lipoma and an intramedulary hematoma on fast spin-echo MRI scans: a case report].

We describe differentiation of a spinal intramedullary lipoma from an intramedullary hematoma on magnetic resonance images (MRI) with fast spin-echo (FSE) sequences. A 60-year-old man with dysesthesia in the legs and gait disturbance, was suspected of having myelopathy at a middle thoracic lesion. MRI with FSE sequences revealed an intramedullary lesion at T7 to T8. On the basis of hyperintensity on both T1-and T2-weighted images and a perilesional hypointense rim on T2-weighted images we made a diagnosis of subacute hematoma and planned observation. However, computed tomography for associated vertebral degeneration revealed a hypodense area (-97 Hounsfield units) in the region corresponding to the lesion depicted by MRI. We revised our diagnosis to an intramedullary lipoma and debulked the lesion. The lipoma was surrounded by a thick whitish capsule. Histopathologically, the capsule contained mature fat tissue and abundant collagen. The initial diagnosis was mainly attributable to specific FSE characteristics, i. e., the depiction of fat tissue as hyperintense on both T1-and T2-weighted images. Conventional spin-echo MRI depicts fat tissue as hyperintense on T1-and as hypointense on T2-weighted images. Other factors contributing to our initial diagnosis were MRI findings suggestive of an intramedullary hematoma, i. e., the intrinsic location of the lesion and the perilesional hypointense rim on T2-weighted images ascribable to collagen present in the capsule. The accurate diagnosis of an intramedullary lipoma on FSE requires correct interpretation of the signal, which is different from the signal on conventional spin-echo MRI.

Prospective study of superior cluneal nerve disorder as a potential cause of low back pain and leg symptoms.

BACKGROUND: Entrapment of the superior cluneal nerve (SCN) in an osteofibrous tunnel has been reported as a cause of low back pain (LBP). However, there are few reports on the prevalence of SCN disorder and there are several reports only on favorable outcomes of treatment of SCN disorder on LBP. The purposes of this prospective study were to investigate the prevalence of SCN disorder and to characterize clinical manifestations of this clinical entity. METHODS: A total of 834 patients suffering from LBP and/or leg symptoms were enrolled in this study. Diagnostic criteria for suspected SCN disorder were that the maximally tender point was on the posterior iliac crest 70 mm from the midline and that palpation of the tender point reproduced the chief complaint. When patients met both criteria, a nerve block injection was performed. At the initial evaluation, LBP and leg symptoms were assessed by visual analog scale (VAS) score. At 15 min and 1 week after the injection, VAS pain levels were recorded. If insufficient pain decrease or recurrence of pain was observed, injections were repeated weekly up to three times. Surgery was done under microscopy. Operative findings of the SCN and outcomes were recorded. RESULTS: Of the 834 patients, 113 (14%) met the criteria and were given nerve block injections. Of these, 54 (49%) had leg symptoms. Before injection, the mean VAS score was 68.6 ± 19.2 mm. At 1 week after injection, the mean VAS score significantly decreased to 45.2 ± 28.8 mm (p < 0.05). Ninety-six of the 113 patients (85%) experienced more than a 20 mm decrease of the VAS score following three injections and 77 patients (68%) experienced more than a 50% decrease in the VAS score. Surgery was performed in 19 patients who had intractable symptoms. Complete and almost complete relief of leg symptoms were obtained in five of these surgical patients. CONCLUSIONS: SCN disorder is not a rare clinical entity and should be considered as a cause of chronic LBP or leg pain. Approximately 50% of SCN disorder patients had leg symptoms.

Heteropolyacid-catalyzed direct deoxygenation of propargyl and allyl alcohols.

The combination of H(3)[PW(12)O(40)]·nH(2)O (1 mol %) and Et(3)SiH led to the direct catalytic deoxygenation of propargyl alcohols, in which proper solvent selection Cl(CH(2))(2)Cl vs CF(3)CH(2)OH was the key to obtaining better product yields. Under similar conditions, the deoxygenation of allyl alcohols proceeded to give thermodynamically stable alkenes with migration of the double bonds in good yields.

Dual control by regulators, GntH and GntR, of the GntII genes for gluconate metabolism in Escherichia coli.

Escherichia coli possesses two systems, GntI and GntII, for gluconate uptake and catabolism, whose genes are regulated by GntR as a repressor and GntH as an activator, respectively. Additionally, GntH exerts negative control of the GntI genes via the same binding element as that of GntR. We thus examined whether GntR involves regulation of the GntII genes or not. This regulation and the control by GntH were examined by using single-copy LACZ operon fusions and by RT-PCR, suggesting positive and negative regulation by GntR and positive regulation by GntH. Moreover, the introduction of mutations into possible GntR-binding elements revealed that both regulators share at least one of the elements. The results presented allow us to speculate that GntR initiates expression of the GntII genes, followed by their large induction by GntH when cells were grown in gluconate minimum medium. As in the case of the GntI genes, such a cross-regulation between the GntI and GntII via the two regulators may be important for cells to grow with gluconate.

The activator of GntII genes for gluconate metabolism, GntH, exerts negative control of GntR-regulated GntI genes in Escherichia coli.

Gluconate is one of the preferred carbon sources of Escherichia coli, and two sets of gnt genes (encoding the GntI and GntII systems) are involved in its transport and metabolism. GntR represses the GntI genes gntKU and gntT, whereas GntH was previously suggested to be an activator for the GntII genes gntV and idnDO-gntWH. The helix-turn-helix residues of the two regulators GntR and GntH exhibit extensive homologies. The similarity between the two regulators prompted analysis of the cross-regulation of the GntI genes by GntH. Repression of gntKU and gntT by GntH, as well as GntR, was indeed observed using transcriptional fusions and RNA analysis. High GntH expression, from cloned gntH or induced through 5-ketogluconate, was required to observe repression of GntI genes. Two GntR-binding elements were identified in the promoter-operator region of gntKU and were also shown to be the target sites of GntH by mutational analysis. However, the GntI genes were not induced by gluconate in the presence of enhanced amounts of GntH, whereas repression by GntR was relieved by gluconate. The repression of GntI genes by GntH is thus unusual in that it is not relieved by the availability of substrate. These results led us to propose that GntH activates GntII and represses the GntI genes in the presence of metabolites derived from gluconate, allowing the organism to switch from the GntI to the GntII system. This cross-regulation may explain the progressive changes in gnt gene expression along with phases of cell growth in the presence of gluconate.