Inhibitory copper binding site on the spinach cytochrome b6f complex: implications for Qo site catalysis

The isolated cytochrome (cyt) b(6)f complex from spinach is inhibited by Cu(2+) with a K(D) of about 1 microM at pH 7.6 in the presence of 1.6 microM decyl-plastoquinol (C(10)-PQH(2)) as a substrate. Inhibition was competitive with respect to C(10)-PQH(2) but noncompetitive with respect to horse heart cyt c or plastocyanin (PC). Inhibition was also pH-sensitive, with an apparent pK at about 7, above which inhibition was stronger, suggesting that binding occurred at or near a protonatable amino acid residue. Equilibrium binding titrations revealed ca. 1.4 tight Cu(2+) binding sites with a K(D) of about 0.5 microM and multiple (>8) weak (K(D) > 50 microM) binding sites per complex. Pulsed electron paramagnetic resonance (EPR) techniques were used to identify probable binding sites for inhibitory Cu(2+). A distinct enhancement of the relaxation time constant for the EPR signal from bound Cu(2+) was observed when the cyt f was paramagnetic. The magnitude and temperature-dependence of this relaxation enhancement were consistent with a dipole interaction between Cu(2+) and the cyt f (Fe(3+)) heme at a distance of between 30 and 54 A, depending upon the relative orientations of Cu(2+) and cyt f heme g-tensors. Two-pulse electron spin-echo envelope modulation (ESEEM) and 4-pulse 2-dimensional hyperfine sublevel correlation (2D HYSCORE) measurements of Cu(2+) bound to isolated cyt b(6)f complex indicated the presence of a weakly coupled nitrogen nucleus. The nuclear quadrupole interaction (NQI) and the hyperfine interaction (HFI) parameters identified one Cu(2+) ligand as an imidazole nitrogen of a His residue, and electron-nuclear double resonance (ENDOR) confirmed the presence of a directly coordinated nitrogen. A model of the 3-dimensional structure of the cytochrome b(6)f complex was constructed on the basis of sequences and structural similarities with the mitochondrial cyt bc(1) complex, for which X-ray structures have been solved. This model indicated three possible His residues as ligands to inhibitory Cu(2+). Two of these are located on the "Rieske" iron-sulfur protein protein (ISP) while the third is found on the cyt f protein. None of these potential ligands appear to interact directly with the quinol oxidase (Q(o)) binding pocket. A model is thus proposed wherein Cu(2+) interferes with the interaction of the ISP protein with the Q(o) site, preventing the binding and subsequent oxidation of plastoquinonol. Implications for the involvement of ISP "domain movement" in Q(o) site catalysis are discussed.

Wrinkling due to mid-dermal elastolysis: two cases and literature review

BACKGROUND

Mid-dermal elastolysis is an acquired disorder of elastic tissue clinically characterized by diffuse fine wrinkling, most often of the trunk and arms. Histologically, a clear band of elastolysis is present in the mid-dermis.

OBJECTIVE

Although examples of diffuse elastolysis are well known, only a small number of patients with mid-dermal elastolysis have been reported to date. We present two patients with clinical and histological evidence of mid-dermal elastolysis, review the literature, and summarize the salient features of some common disorders of elastic tissue.

METHODS

The first patient presented with fine wrinkles and papules over the upper arms, upper chest, and axillae, and demonstrated increased laxity of the eyelids. The second patient had striking wrinkles extending in a band-like pattern on her arms, upper chest, back, and abdomen. Neither one of our patients had a previous history of skin inflammation, urticaria, or any other underlying diseases related to their skin changes. Skin biopsies were taken from lesional and perilesional skin of both patients, and were stained with hematoxylin and eosin, and with elastic tissue stain. In addition, a tissue sample from Patient 1 was fixed for electron-microscopy.

RESULTS

Hematoxylin and eosin stains did not demonstrate specific changes or diagnostic patterns. However, elastic tissue stains revealed a band-like loss of elastic tissue in the mid-dermis. Elastic tissue in the remaining superficial and deep dermis stained normally. Electron-microscopy was consistent with these findings and revealed significant loss of elastic tissue limited to the mid-dermis.

CONCLUSION

We have presented two cases of mid-dermal elastolysis and reviewed the literature. To date, the pathophysiology of mid-dermal elastolysis had not been elucidated and no definitive therapy exists.

Antidiabetic and hypolipidemic effects of Momordica cymbalaria Hook. fruit powder in alloxan-diabetic rats

This study was undertaken to investigate the effect of Momordica cymbalaria fruit powder on blood glucose and other biochemical parameters in alloxan-induced diabetic rats. The treatment was given for 15 days. After the treatment, a significant reduction was observed in fasting blood glucose levels in the treated diabetic rats, but no hypoglycaemic activity in the treated normal rats. M. cymbalaria treatment showed considerable lowering of serum cholesterol and triglycerides in the treated diabetic group. There was a significant improvement in hepatic glycogen level in treated diabetic rats close to normal level after the treatment with M. cymbalaria. These results suggest that the M. cymbalaria fruit powder possesses antidiabetic and hypolipidemic effects in alloxan-induced diabetic rats.

Involvement of nitric oxide (NO) in hypoglycaemic activity of tolbutamide

The study was conducted to find the involvement of Nitric Oxide (NO) using L-arginine, a NO precursor and NG-methyl L-arginine a nitric oxide synthase inhibitor on tolbutamide activity in normal rabbits. L-arginine (25-300 mg/kg, body weight, oral) produced transient and dose dependent hypoglycaemia. When combined with tolbutamide (40 mg/kg, oral) it produced early and prolonged action. The effect of tolbutamide was blocked by NG-methyl L-arginine (5 mg/kg, body weight, oral). The results confirm the involvement of NO in tolbutamide activity and the possibility of using L-arginine as a supplement to antidiabetic drugs in blood glucose control.

Risk of melanoma in medium-sized congenital melanocytic nevi: a follow-up study

BACKGROUND

The risk of the occurrence of malignant melanoma (MM) in medium-sized (1.5 to 19.9 cm in diameter) congenital melanocytic nevi (CMN) is the subject of controversy. Universally accepted recommendations regarding the management of such lesions have not been made.

OBJECTIVE

Our purpose was to assess the risk of MM arising in medium-sized CMN.

METHODS

The study included 230 medium-sized CMN in 227 patients, first seen in a private dermatology practice from 1955 to 1996, who were followed up for MM arising within their CMNs. Criteria for entry into the study included (1) a clinically diagnosed medium-sized CMN, (2) minimum follow-up period of 1 year, and (3) a photograph of the lesion in the patient's medical record.

RESULTS

No MM occurred in a medium-sized CMN during an average follow-up of 6.7 years (median, 5.8 years) to an average age of 25.5 years (median, 19.1 years).

CONCLUSION

The results of this short-term follow-up study do not support the view that there is a clinically significantly increased risk for MM arising in banal-appearing medium-sized CMN or that prophylactic excision of all such lesions is mandatory. Lifelong medical observation seems a reasonable alternative for many medium-sized CMN.

Carcinoid tumour: laser therapy

A 31-year-old female, pregnant (I trimester), presented with symptoms and signs of bronchial asthma. Chest roentgenogram and computerized tomography of the chest revealed right mid and lower zone opacity (collapse). Bronchoscopic examination revealed intrabronchial growth in the right middle and lower lobe bronchus. Biopsy and histopathological examination confirmed carcinoid tumour. These symptoms and signs disappeared after laser therapy. The lesion, however, recurred two years later.

A study of large congenital melanocytic nevi and associated malignant melanomas: review of cases in the New York University Registry and the world literature

BACKGROUND

Patients with large congenital melanocytic nevi (LCMN) are at greater risk for the development of malignant melanoma (MM) than are persons in the general population.

OBJECTIVE

Our purpose was to identify the clinical features of LCMN in those patients in whom MMs actually developed.

METHODS

The records of 117 patients in the New York University Registry of LCMN and the reports of 172 cases of LCMN in the world literature were studied.

RESULTS

Of the 289 cases of LCMN studied, 34 patients (12%) had primary cutaneous MMs within their nevi; in two additional patients, MMs developed at cutaneous sites other than within their nevi. All patients in whom MM developed within LCMN had nevi in axial locations; however, 91% of the LCMN were axial. No MM was found that had arisen in any of the 26 LCMN confined to the extremities. In addition, no MM was found that had arisen in thousands of satellite nevi.

CONCLUSION

When MM develops within an LCMN, it generally does so in those LCMN in an axial location. The absence of cases of MM arising in LCMN confined to the extremities suggests that such nevi represent lower risk lesions, but the number of extremity nevi analyzed was too small to allow definitive conclusions. A striking finding was the absence of MMs arising in satellite nevi.

Neurocutaneous melanosis: clinical features of large congenital melanocytic nevi in patients with manifest central nervous system melanosis

BACKGROUND

Patients with a large congenital melanocytic nevus (LCMN) may have associated leptomeningeal melanocytosis with or without central nervous system (CNS) melanomas. These patients are considered to have neurocutaneous melanosis, a disorder that, when symptomatic or otherwise manifest neurologically, carries a poor prognosis even in the absence of malignancy.

OBJECTIVE

Our purpose was to identify typical clinical features in patients who have manifest CNS melanosis in association with LCMN.

METHODS

The records of 117 patients with LCMN in the New York University Registry of LCMN and the reports of 172 cases of LCMN in the world literature were included for features that might signal a high risk for the development of manifest CNS involvement.

RESULTS

Of the 289 patients with LCMN, 33 had manifest CNS melanosis. In all 33 in whom symptomatic neurocutaneous melanosis was diagnosed, the LCMNs were present in a posterior axial location on the head, neck, back, and/or buttocks. "Satellite" nevi were known to be present in 31 of the 33 patients.

CONCLUSION

Patients with LCMN in a posterior axial location, especially when associated with "satellite" melanocytic nevi, are at greater risk for the development of manifest neurocutaneous melanosis than patients with LCMN limited to the extremities or those who are lacking satellite nevi.