A novel method produces native light-harvesting complex II aggregates from the photosynthetic membrane revealing their role in nonphotochemical quenching.

Nonphotochemical quenching (NPQ) is a mechanism of regulating light harvesting that protects the photosynthetic apparatus from photodamage by dissipating excess absorbed excitation energy as heat. In higher plants, the major light-harvesting antenna complex (LHCII) of photosystem (PS) II is directly involved in NPQ. The aggregation of LHCII is proposed to be involved in quenching. However, the lack of success in isolating native LHCII aggregates has limited the direct interrogation of this process. The isolation of LHCII in its native state from thylakoid membranes has been problematic because of the use of detergent, which tends to dissociate loosely bound proteins, and the abundance of pigment-protein complexes (e.g. PSI and PSII) embedded in the photosynthetic membrane, which hinders the preparation of aggregated LHCII. Here, we used a novel purification method employing detergent and amphipols to entrap LHCII in its natural states. To enrich the photosynthetic membrane with the major LHCII, we used Arabidopsis thaliana plants lacking the PSII minor antenna complexes (NoM), treated with lincomycin to inhibit the synthesis of PSI and PSII core proteins. Using sucrose density gradients, we succeeded in isolating the trimeric and aggregated forms of LHCII antenna. Violaxanthin- and zeaxanthin-enriched complexes were investigated in dark-adapted, NPQ, and dark recovery states. Zeaxanthin-enriched antenna complexes showed the greatest amount of aggregated LHCII. Notably, the amount of aggregated LHCII decreased upon relaxation of NPQ. Employing this novel preparative method, we obtained a direct evidence for the role of in vivo LHCII aggregation in NPQ

Unusual clinical manifestation of pheochromocytoma in a MEN2A patient

A case of unusual clinical manifestation of pheochromocytoma in a type 2A multiple endocrine neoplasia (MEN2A) patient is presented. A 27-year-old man affected by MEN2A syndrome, complaining of anxiety and depression, was admitted in our Division. Past medical history included a total thyroidectomy for medullary carcinoma in 1985, and left adrenalectomy for pheochromocytoma in 1994. Blood pressure was 130/ 85 mmHg without orthostatic hypotension and pulse rate was 72 beats/min. Laboratory data revealed thyroid hormones and carcinoembryonic antigen (CEA) in the normal range and high basal serum calcitonin levels (158 pg/ml). Plasma catecholamines and vanillylmandelic acid resulted in normal levels but epinephrine/norepinephrine ratio was elevated (0.65). The glucagon stimulation test showed positive clinical and biochemical response. Magnetic resonance imaging (MRI) and meta-iodobenzylguanidine (MIBG) scintiscan confirmed the presence of bilateral adrenal masses. Bilateral adrenalectomy by laparoscopic anterior approach was performed. Histology was consistent with adrenal pheochromocytomas. After surgical approach, psychiatric findings disappeared and did not recur at follow-up in spite of no medication for two years. In conclusion, bilateral pheochromocytoma is more frequent in MEN2A syndrome and probably understimated if the follow-up is not prolonged. In these cases clinical features are often aspecific and basal hormonal data may be normal in a great number of patients. Therefore long-term observation is justified in these patients. Pheochromocytoma was described as the "great mimic" for the numerous subjective manifestations. Differential diagnosis amon