Compartmentation of high-energy phosphates in resting and beating heart cells

The subcellular distribution of ATP, ADP, creatine phosphate and creatine has been analyzed by fast detergent fractionation of isolated frog heart cells. Digitonin fractionation (0.5 mg/ml, 10 s at 2 degrees C in 20 mM 4-morpholinepropanesulfonic acid/3 mM EDTA/230 mM mannitol medium) was used to separate mitochondria and myofilaments from cytosol. To separate myofilaments from the other cellular compartments. Triton X-100 was used (2%, 15 s in the same medium as digitonin). For either resting or beating cells the total cellular contents of ATP, ADP, creatine phosphate and creatine was similar, nevertheless the O2 consumption was 6-times higher. The compartmentation of these metabolites was also identical. Myofilaments contain 1.1 nmol ADP per mg total cellular proteins. In the cytosolic compartment the metabolite concentrations, all measured in nmol per mg total cellular proteins, were: ATP, 13; ADP, 0.25-0.05; creatine phosphate, 18.5 and creatine, 14. This indicated that the reaction catalyzed by creatine kinase was in a state of (or near) equilibrium.     

Effects of antimicrotubular agents in cAMP production and in steroidogenic response of isolated rat Leydig cells

In dispersed rat Leydig cells, colchicine was found to stimulate basal cAMP production and testosterone secretion in a dose and time-dependent manner, but to a lesser extent than LH. However, these drugs are unable to stimulate adenylate cyclase activity in plasma membranes isolated from these cells. The amount of testosterone secreted at 150 min under the influence of colchicine and LH added simultaneously was not different from the amount produced during stimulation by LH alone. It is only after exposure of the cells for 1 hr to colchicine that the accumulation of cAMP in response to LH was inhibited; furthermore, both intracellular and medium testosterone accumulation in response to the hormone were reduced. Similar effects were observed with two other alkaloids, vinblastine and podophyllotoxin. The three drugs also inhibited the stimulation of testosterone secretion by 8-Br-cAMP or choleratoxin. These studies suggest that the state of microtubule polymerization and/or tubulin can influence the process of steroidogenesis in rat Leydig cells.     

Decomposition of three halophytes in different habitats of an eastern scheldt salt marsh

Summary A 20.5-month study was undertaken to determine detrital processing of the halophytesSpartina anglica, Elytrigia pungens, andHalimione portulacoides in three different habitats of an estuarine salt marsh in the South-West Netherlands. Decomposition was measured using litter-bags of three different mesh sizes to partition the effects of different faunal groups on decomposition. From April 1980 through October 1981 litter-bags were sampled regulary from a creek, the upper marsh, and from a plant-debris belt on the higher marsh. Dry weights and nutritive values were measured and animals were counted. Mainly rates of loss are reported here. Zonal differences were significant. At first, decomposition in the creek was most rapid. After two months the processes in the creek slowed down because of the trapping of silt by the bags, which probably simulated the natural course of the decomposition process in the water. Decomposition on the marsh followed the most regular pattern, while in the plant-debris belt the pattern was very irregular. Population dynamics of microfaunal organisms supported these findings. In the plant-debris belts loss rates seem to be higher than on the marsh, because of the influence of detritivorous macrofaunal organisms. The loss rates of the three plant species differed significantly.Halimione decomposed fastest, especially in the beginning, and in the plant-debris habitat. On the upper marsh and in the plant-debris belt the loss rates ofSpartina seem to be a little higher than those ofElytrigia.Communication No. 233, Delta Institute for Hydrobiological Research, Yerseke, The Netherlands.     

Hexapeptide analogue of somatostatin, Sandoz 201-456. Conformational study in dimethylsulfoxide by 1D and 2D n.m.r. methods

The conformational properties of the somatostatin analogue 201-456 (1) have been studied by high field n.m.r. in DMSO. This analogue is the base structure of nine derivates synthesized by Bauer et al. and shows a very low biological activity, although derived structures such as SMS 201-995 (2) are very potent. Our study has shown an important difference between the most stable conformation of the two compounds: although the beta turn type II' structure at the Phe3-Trp4-Lys5 level is present in both analogues, an important conformational change appears at the cystine bridge. In SMS 201-995 the beta turn/beta sheet conformation is stabilized by the additional amino-acids D-Phe1 and Thr8 (ol) through intramolecular H-bonds.     

Calcium-stimulated myofibrillar ATPase activity correlates with shortening velocity of muscle fibres in Xenopus laevis

Summary The iliofibularis muscle ofXenopus laevis is reported to contain five types of fibres which have different force—velocity relationships. Ten fibres of each type were selected on the basis of succinate dehydrogenase activity, cross-sectional area and location in the muscle, in order to assess the validity of the fibre type classification.Maximum calcium-stimulated myofibrillar ATPase activity (V _max) and apparent Michaelis constant (K _m) for ATP were determined for these 50 fibres from serial sections. The values obtained varied according to the type of fibre. Type 1 had the highest and type 5 the lowest values forK _m andV _max.In a separate experiment, single freeze-dried fibres were used to determine the relationship between their ATP content and apparentK _m for ATP. There was a tendency for high ATP concentrations in fibres with highK _m values.When myofibrillar ATPase activity was related to the maximum velocity of shortening of the five fibre types, a significant correlation was found. It is concluded that calcium-stimulated myofibrillar ATPase histochemistry allows an estimate of the maximum shortening velocity of muscle fibres fromXenopus laevis.     

Direct Comparisons of 2D and 3D Dental Microwear Proxies in Extant Herbivorous and Carnivorous Mammals

The analysis of dental microwear is commonly used by paleontologists and anthropologists to clarify the diets of extinct species, including herbivorous and carnivorous mammals. Currently, there are numerous methods employed to quantify dental microwear, varying in the types of microscopes used, magnifications, and the characterization of wear in both two dimensions and three dimensions. Results from dental microwear studies utilizing different methods are not directly comparable and human quantification of wear features (e.g., pits and scratches) introduces interobserver error, with higher error being produced by less experienced individuals. Dental microwear texture analysis (DMTA), which analyzes microwear features in three dimensions, alleviates some of the problems surrounding two-dimensional microwear methods by reducing observer bias. Here, we assess the accuracy and comparability within and between 2D and 3D dental microwear analyses in herbivorous and carnivorous mammals at the same magnification. Specifically, we compare observer-generated 2D microwear data from photosimulations of the identical scanned areas of DMTA in extant African bovids and carnivorans using a scanning white light confocal microscope at 100x magnification. Using this magnification, dental microwear features quantified in 2D were able to separate grazing and frugivorous bovids using scratch frequency; however, DMTA variables were better able to discriminate between disparate dietary niches in both carnivorous and herbivorous mammals. Further, results demonstrate significant interobserver differences in 2D microwear data, with the microwear index remaining the least variable between experienced observers, consistent with prior research. Overall, our results highlight the importance of reducing observer error and analyzing dental microwear in three dimensions in order to consistently interpret diets accurately.     

The ilvIH operon of Escherichia coli K-12. Identification of the gene products and recognition of the translational start by polypeptide microsequencing

The ilvI and ilvH gene products were identified physically by electrophoretic analysis of in vivo-labelled polypeptides produced in minicells from plasmids carrying the wild-type ilvIH operon of Escherichia coli K-12 and derivatives of it. An analysis of the distribution of methionine residues in the amino-terminal portion of micro-quantities of the ilvI product eluted from gel showed that the translational start of the ilvI gene is the promoter-proximal one of three putative methionine codons predicted from the DNA sequence.