Marker-free method for accurate alignment between correlated light,cryo-light,and electron cryo-microscopy data using sample support features

Combining fluorescence microscopy with electron cryo-tomography allows, in principle, spatial localization of tagged macromolecular assemblies and structural features within the cellular environment. To allow precise localization and scale integration between the two disparate imaging modalities, accurate alignment procedures are needed. Here, we describe a marker-free method for aligning images from light or cryo-light fluorescence microscopy and from electron cryo-microscopy that takes advantage of sample support features, namely the holes in the carbon film. We find that the accuracy of this method, as judged by prediction errors of the hole center coordinates, is better than 100?nm.     

Carbon-13 nmr spectra of vitamin B6 compounds: Aqueous solution equilibria and determination of microscopic acid dissociation constants

The aqueous solution equilibria and solute structure of vitamin B₆ compounds and several model compounds have been investigated using ¹³C-nmr spectroscopy. The unsubstituted α-carbon of these compounds is a very good probe for data which permits assignment of the ionization steps to indicidual groups. While the ionizations of the pyridinium and phenolic groups take place simultaneously in 3-hydroxypyridine, they take place in well-separated steps in pyridoxamine (PM), pyridoxamine phosphate (PMP), and pyridoxal phosphate. It has been established that the ionization with a pK_a value of 3.7 is predominantly phenolic in origin in PM and PMP. A zwitterionic structure consistent with the earlier spectroscopic investigations is proposed for the vitamin B₆ compounds in neutral aqueous solution.     

Membrane potentials of human fibroblast strains in culture

With a simple technique, the membrane electro-physiology of mammalian fibroblasts in tissue culture can be explored with micro-electrodes. Measured in complete, serum-containing medium, the mean membrane potential for human diploid cell strains in between 70 and 75 millivolts.     

The digestive gland of the Southern Dumpling Squid (Euprymna tasmanica): structure and function

The cephalopod digestive gland plays an important role in the efficient assimilation of nutrients and therefore the fast growth of the animal. The histological and enzymatic structure of Euprymna tasmanica was studied and used in this experiment to determine the dynamics of the gland in response to feeding. The major roles of the digestive gland were secretion of digestive enzymes in spherical inclusions (boules) and excretion of metabolic wastes in brown body vacuoles. High levels of trypsin, chymotrypsin and α-amylase, low levels of α-glucosidase and negligible carboxypeptidase activity were produced by the gland. There was no evidence of secretion of digestive enzymes in other organs of the digestive tract. Within 60 min of a feeding event, the gland produced increasing numbers of boules to replace those lost from the stomach during the feeding event. Initially, small boules were seen in the digestive cells, they increased in size until they are released into the lumen of the gland where they are transported to the stomach. There was no evidence of an increase in activity of digestive enzymes following a feeding event, despite structural changes in the gland. However, there was large variation among individuals in the level of digestive enzyme activity. A negative correlation between boule and brown body vacuole density suggested that the large variation in enzyme activity may be due to the digestive gland alternating between enzyme production and excretion.     

Extreme hydrologic banding in a large-river Floodplain, California, U.S.A.

Where tributaries meet, certain conditions of flow and topography often result in incomplete mixing and the formation of spatially and temporally persistent plumes or bands. Yolo Bypass, the primary floodplain of the lower Sacramento River (California, USA), provides an extreme example of this effect. Inspection of recent and historical aerial photographs revealed that the four major tributaries of Yolo Bypass typically do not substantially mix laterally within the floodplain. The phenomenon is notable in the number of tributaries involved (4), the distance over which the bands remain distinct (>61 km), and the persistence of the bands despite channel constrictions and long cross-wind fetch. This effect demonstrates the importance of lateral variability during floodplain flow events, including transport and distribution of chemical constituents, and habitat for fish and other organisms that use floodplains as migration corridors and rearing areas. Handling editor: S. M. Thomaz