AN ESTIMATION OF PROLIFERATIVE POPULATION SIZE IN STOMACH, JEJUNUM AND COLON OF DBA-2 MICE

Liquid scintillation and autoradiographic techniques have been used to provide quantitative data on the proliferative units, the crypts, of stomach, jejunum and colon of DBA-2 mice. A slight modification of the crypt squash technique has provided data suggesting that about 50% of the cells of the jejunal crypt are at any given time in the proliferative state. This value is lower in the colon while in the stomach glands only 20% of the cells are involved in cell production. The data provide estimates for cell cycle times of 26·3, 16·0 and 23·2 hr for stomach, jejunum and colon respectively.
The size and number of proliferative units have been determined for three regions of the gastrointestinal tract of mice. A review of the literature suggests that considerable strain differences may exist.     

The relationship between hsp 70 localization and heat resistance

Using indirect immunofluorescence we have investigated the kinetics of nuclear accumulation and removal of hsp 70 in HA-1 Chinese hamster fibroblasts exposed to elevated temperatures. The kinetics of accumulation of hsp 70 in the nuclei were found to be time/temperature dependent at all temperatures tested (42-45 degrees C). At a given temperature, the fraction of cells manifesting nuclear localization of hsp 70 increased with exposure time. For a given duration of heating, the fraction of cells manifesting nuclear localization of hsp 70 increased with the temperature. The kinetics of the nuclear accumulation of hsp 70 were similar for normal HA-1 cells, their heat-resistant variants, and transiently thermotolerant cells (triggered by prior exposure to a brief heat shock or to sodium arsenite). Upon return to 37 degrees C after heat shock, the kinetics of removal of the hsp 70 associated with the nucleus was dependent on the severity of the initial heat challenge. However, for a given heat dose, the decay of nuclear localization of hsp 70 was more rapid in thermotolerant and heat-resistant cells than in their normal counterparts. These results suggest that the increased levels of hsp 70 associated with the transient or permanently heat-resistant state may play a direct role in restoring and/or repairing heat-induced nuclear and nucleolar alterations associated with heat-induced cell killing. Furthermore, they also suggest that the heat-resistant state may involve ameliorated repair of heat-induced cellular alterations.     

Determination of stoichiometric association constants by a non-iterative computational method

Computational methods for the estimation of stoichiometric associationconstants for multiple-ligand binding systems are currentlybased on non-linear least-squares regression analysis. Thesecomputational methods require sophisticated, iterative algorithmsto assure convergence to a solution, as well as initial parameterand error estimates. A simple procedure, called lambda-invariancetesting (LIT), was developed that provides a single-pass (non-iterative)estimation of stoichiometric association constants. The LITmethod was applied to simulated binding data containing Gaussianerror and to real data drawn from the literature. This methodprovided parameter estimates essentially equivalent to thoseobtained by least-squares regression analysis, with no initialparameter or error estimates required. Received on May 26, 1987; accepted on July 27, 1987     

Chloroplast thylakoid membrane proteins having buried amine buffering groups

Some chloroplast thylakoid membrane proteins have anomalously low pK_a (near 7.8) amine groups, indicating that the buffering groups may be buried in hydrophobic regions and/or close to other positive charges. Other work has shown that the low pK_a amine group array is not in ready equilibrium with either the inner or outer bulk aqueous phases (Laszlo, J.A., Baker, G.M. and Dilley, R.A. (1984) J. Bioenerg. Biomembranes, 16, 37–51). Acetic anhydride reacts with the neutral amine and has been used as a probe for labeling the low pK_a amines. The buried array of buffering groups can be labeled with [³H]acetic anhydride in the dark only after the membranes were made leaky to protons with uncoupler addition. Sodium dodecyl sulfate/urea-polyacrylamide gel electrophoresis was used to separate the polypeptides and identify those that show the uncoupler-dependent labeling increase. Included in that group are polypeptides known to be associated with Photosystem II having M_r 17000, 22000 and 31000, some of the light-harvesting pigment proteins with M_r 24000–28000, the CF₀ component with M_r 8000 and some polypeptides associated with Photosystem I. A protein with M_r 15000 showed very large changes in labeling, but the identity of this polypeptide is unknown. The arrays of buried amine buffering groups are diversely distributed among membrane proteins and it is not clear what role, if any, they play in membrane function.     

Fine structural and cytochemical analysis of phragmosomes (microbodies) during cytokinesis inAllium root tip cells

Summary The ontogeny and distribution of phragmosomes (microbodies) during cytokinesis inAllium sativum root tip cells have been studied and complemented with a cytochemical analysis of reactivity with diaminobenzidine (DAB). Incubation in different DAB media revealed the presence of catalase but not peroxidase in these organelles, identifying them as a type of microbody associated with the forming cell plate. Only vacuoles, segments of endoplasmic reticulum and portions of the mature walls stained positively with DAB for peroxidase activity. Microbodies begin to appear in the region of the future cell plate as cells enter late anaphase. They exhibit a moderately electron-opaque anucleoid matrix and are continuous with segments of endoplasmic reticulum (ER). Certain observations have led us to consider that certain aspects of plate formation inAllium require the participation of microbodies: (a) their pronounced numerical increase at the onset of plate formation, (b) their intimate association with regions of the plate where vesicle fusion is in progress, and (c) their rapid numerical decline following vesicular fusion and concomitant cell plate formation. The characteristic spatial association observed between microbodies and the plate-forming vesicles may well reflect their mutual involvement in the metabolism of carbohydrates comprising the middle lamella, being coordinated by metabolic activities in the cytosol, mitochondria and dictyosomes.This study was supported in part by NIH training grant HD 174 to Dr.Hewson Swift and the Marquette University Committee on Research Grants 5641 and 5532.     

Rock phosphate solubilization by abiotic and fungal-produced oxalic acid: reaction parameters and bioleaching potential

Oxalic acid-producing fungi play an important role in biogeochemical transformations of rocks and minerals and possess biotechnological potential for extraction of valuable elements from primary or waste ores and other solid matrices. This research investigates the extraction of phosphate from rock phosphate (RP) by oxalic acid. Reaction parameters were derived using pure oxalic acid solutions to solubilize RP. It was found that the oxalic acid concentration was the main factor driving reaction kinetics. Excess oxalic acid could retard the reaction due to calcium oxalate encrustation on RP surfaces. However, complete P extraction was reached at stoichiometric proportions of apatite and oxalic acid. This reaction reached completion after 168 h, although most of the P (up to 75%) was released in less than 1 h. Most of the Ca released from the apatite formed sparingly soluble calcium oxalate minerals, with a predominance of whewellite over weddellite. Bioleaching of RP employing biomass-free spent culture filtrates containing oxalic acid (100 mM) produced by Aspergillus niger extracted ~ 74% of the P contained in the RP. These findings contribute to a better understanding of the reaction between apatite and oxalic acid and provide insights for potential applications of this process for biotechnological production of phosphate fertilizer.