Crystal structure of the O intermediate of the Leu93→Ala mutant of bacteriorhodopsin.

The lifetime of the O intermediate of bacteriorhodopsin (BR) is extended by a factor of ∼250 in the Leu93-to-Ala mutant (BR_L93A). To clarify the structural changes occurring in the last stage of the proton pumping cycle of BR, we crystallized BR_L93A into a hexagonal P622 crystal. Diffraction data from the unphotolyzed state showed that the deletion of three carbon atoms from Leu93 is compensated by the insertion of four water molecules in the cytoplasmic vicinity of retinal. This insertion of water is suggested to be responsible for the blue-shifted λ(max) (540 nm) of the mutant. A long-lived substate of O with a red-shifted λ(max) (~565 nm) was trapped when the crystal of BR_L93A was flash-cooled after illumination with green light. This substate (O(slow)) bears considerable similarity to the M intermediate of native BR; that is, it commonly shows deformation of helix C and the FG loop, downward orientation of the side chain of Arg82, and disruption of the Glu194/Glu204 pair. In O(slow), however, the main chain of Lys216 is less distorted and retinal takes on the 13-cis/15-syn configuration. Another significant difference is seen in the pH dependence of the structure of the proton release group, the pK(a) value of which is suggested to be much lower in O(slow) than in M.

Anomalous bifurcation and island formation of the carotid artery.

An anomalous artery directly connecting the common carotid artery and internal carotid artery was discovered on the right side in the cadaver of an 83-year-old Japanese female, and the facial artery, maxillary artery, and superficial temporal artery arose from the common carotid artery by a common trunk. The anomalous artery arose from the posterior aspect of the common carotid artery at the level of the origin of the superior thyroid artery, and joined the posterior aspect of the internal carotid artery. The anomalous artery was covered by the connective tissue surrounding the common carotid artery and the internal carotid artery. The anomalous anastomosis, especially the proximal portion, may have arisen from the second branchial arch artery during development.

Gastroduodenal adenocarcinomas and rectal adenoma in a cougar (Felis concolor) infected with Helicobacter-like organisms and spirochetes.

A 14-year-old female cougar died from gastroduodenal adenocarcinomas and rectal adenoma. At necropsy, polypoid tumor masses of various sizes were scattered on the mucosal surfaces of the stomach, duodenum, and rectum. Histologically, the gastric tumor was diagnosed as an intestinal type adenocarcinoma and the tumor cells metastasized to the mesenteric lymph nodes, spleen, and lung. Helicobacter-like organisms were detected in the lumina lined by foveolar epithelium. In the duodenum, the carcinoma cells were localized in the limina propria and many of them were intensely positive for proliferating cell nuclear antigen (PCNA). In contrast, the rectal adenoma had a lower number of PCNA-positive cells. In the rectum, chronic inflammation with numerous spirochetes was also noted. These results indicated that the occurrence of the gastrointestinal tumors might be associated with the bacterial infection described above.