Akhet Khufu: Archaeo-astronomical Hints at a Common Project of the Two Main Pyramids of Giza, Egypt

Abstract. The architectural complexes composed by the two main pyramids of Giza together with their temples are investigated from an interdisciplinary point of view, taking into account their astronomical alignments as well as their relationships with the visible landscape. Combining already known facts together with new clues, the work strongly supports the idea that the two complexes were conceived as parts of a common project

Secondary Merkel Cell Carcinoma Manifested in the Parotid

Background. Merkel cell carcinoma of the head and neck is a rare and aggressive malignant tumour. Both the dermatological and surgical colleagues should be aware of this entity as lesions usually present on sun exposed areas of the skin such as the head and neck. Main Observation and Treatment. A 69-year-old male originally presented to the maxillofacial surgery department with a growing lesion on the left eyebrow. Histological analysis confirmed Merkel cell carcinoma and consequently surgical excision was carried out. A follow-up PET/CT scan 2 years later demonstrated a hotspot in the left parotid gland. Fine needle aspiration and cytology revealed Merkel cell carcinoma. A subtotal parotidectomy left side with ipsilateral selective neck dissection levels I to III was carried out. Conclusions. Potential secondary Merkel cell carcinoma in the head and neck region should be taken into account when planning short- and long-term follow up for previously diagnosed patients. This followup should involve both dermatological and surgical colleagues

Proton transfer in the oxidative half-reaction of pentaerythritol tetranitrate reductase

The roles of His181, His184 and Tyr186 in PETN reductase have been examined by mutagenesis, spectroscopic and stopped-flow kinetics, and by determination of crystallographic structures for the Y186F PETN reductase and reduced wild-type enzyme—progesterone complex. Residues His181 and His184 are important in the binding of coenzyme, steroids, nitroaromatic ligands and the substrate 2-cyclohexen-1-one. The H181A and H184A enzymes retain activity in reductive and oxidative half-reactions, and thus do not play an essential role in catalysis. Ligand binding and catalysis is not substantially impaired in Y186F PETN reductase, which contrasts with data for the equivalent mutation (Y196F) in Old Yellow Enzyme. The structure of Y186F PETN reductase is identical to wild-type enzyme, with the obvious exception of the mutation. We show in PETN reductase that Tyr186 is not a key proton donor in the reduction of α/β unsaturated carbonyl compounds. The structure of two electron-reduced PETN reductase bound to the inhibitor progesterone mimics the catalytic enzyme-steroid substrate complex and is similar to the structure of the oxidized enzyme-inhibitor complex. The reactive C1-C2 unsaturated bond of the steroid is inappropriately orientated with the flavin N5 atom for hydride transfer. With steroid substrates, the productive conformation is achieved by orientating the steroid through flipping by 180°, consistent with known geometries for hydride transfer in flavoenzymes. Our data highlight mechanistic differences between Old Yellow Enzyme and PETN reductase and indicate that catalysis requires a metastable enzyme-steroid complex and not the most stable complex observed in crystallographic studies