Influence of serum and poliovirus infection on the transport and accumulation of AIB in HeLa cells

The kinetics of active transport of the model amino acid AIB (aminoisobutyric acid) into HeLa cells were analysed. Serum withdrawal from cell-culture medium prior to transport assay strongly lowers the influx and steady-state distribution of AIB. Readdition of serum restores the rate of influx within 30 min, while the capacity to concentrate AIB is only partially reestablished. These changes are due to alterations in the activity of system A. In the time-course of poliovirus infection the initial rate of AIB transport shows two distinct changes. Early in the infection there is an increase in influx, followed by a strong decrease later in infection. These alterations are also attributed to transport system A.     

Optimizing foraging behaviour through learning

Manifestation of life-history strategy is through the allocation of resources acquired by foraging. Foraging efficiency can be improved by learning, as fishes adjust their behaviour to changing circumstances. We briefly review the influence of learning on the foraging behaviour of fishes and make recommendations for further research. We stress the importance of quantifying learning and memory in relation to ontogeny and life history.     

Light-dependent changes in cytoplasmic aspartate aminotransferase activity in rod spherules of the rat retina. A cytochemical study.

The cytoplasmic activity of the glutamate synthesizing enzyme aspartate aminotransferase (c-AAT) has been investigated on the ultrastructure level in rod spherules of light and dark adapted rat retinae using cytochemistry. Although most rod terminals react negatively, in a subpopulation of rods a weak activity, which is observed in light adapted retinae, is markedly increased under dark conditions. This indicates, that in addition to cones, some rods might use glutamate as their transmitter as well.     

Exons encoding the highly conserved part of human glutaminyl-tRNA synthetase

Summary Aminoacyl-tRNA synthetases are important components of the genetic apparatus. In spite of common catalytic properties, synthetases with different amino acid specificities are widely diverse in their primary structures, subunit sizes, and subunit composition. However, synthetases with given amino acid specificities are well conserved throughout evolution. We have been studying the human glutaminyl-tRNA synthetase possessing a sequence of about 400 amino acid residues (the core region) that is very similar to sequences in the corresponding enzymes from bacteria and yeast. The conserved sequence appears to be essential for the basic function of the enzyme, the charging of tRNA with glutamine. As a first step to a better understanding of the evolution of this enzyme, we determined the coding region for the conserved part of the human glutaminyl-tRNA synthetase. The coding region is composed of eight exons. It appears that individual exons encode defined secondary structural elements as parts of functionally important domains of the enzyme. Evolution of the gene by assembly of individual exons seems to be a viable hypothesis; alternative pathways are discussed. Offprint requests to: R. Knippers     

Microtechniques for the gas chromatographic determination of barbiturates in small blood samples

A method for the determination of therapeutic levels of barbituric acids in 25 μl of whole blood is described. After extraction and controlled concentration of the extract to a volume of 5 μl, the barbituric acids are N,N′-dimethylated using a microrefluxer. Of the total extract 20–100% is injected into the gas chromatograph. Low blanks, recoveries of 70–80% and peak ratios that are comparable to those in calibration experiments are obtained provided the detailed working instructions are followed strictly. In addition, barbiturates were determined (1 ng in 25 μl blood) using column-switching devices and nitrogen-sensitive detection.     

Formation of dissociated enzyme subunits by chemical treatment during renaturation

When iodoacetate is added to denatured muscle aldolase undergoing renaturation, a major portion of the activity in the resulting enzyme remains in the monomeric form (of about 37,000 M_r). In the absence of iodoacetate, the renatured enzyme exists entirely as the tetramer. Iodoacetate treatment of native aldolase tetramer (M_r = 160,000) does not lead to dissociation. The stabilization of the monomer by iodoacetate treatment is presumably due to modification of a group at the intersubunit region. Active monomers of aldolase could be distinguished from native or renatured aldolase tetramer by gel-filtration and by the sensitivity of the monomer to inactivation in 2.3 m-urea.     

Autosomal recessively inherited electrolyte excretory defect in the parotid of the "cribriform degeneration" mouse mutant--possible analogy to cystic fibrosis

The mutation in the DBA/2J mice characterized by cribriform degeneration of the central nervous system also fxhibits a genetically determined defect in the transport on Na⁺ by the parotid gland duct. This defect results in the increased Na⁺ concentration of final parotid saliva. The sweat gland of the dorsal foot pad of the mutant mouse does not exhibit this defect. The apparent homology of the electrolyte disturbance in this animal model to the one seen in the autosomal recessively inherited disorder cystic fibrosis of the pancreas is elaborated upon.     

Molecular studies in 37 Silver-Russell syndrome patients: frequency and etiology of uniparental disomy

We report studies on the etiology of uniparental disomy (UPD) in Silver-Russell syndrome (SRS) patients. Thirty-seven SRS families were typed with short tandem repeat markers from chromosomes 2, 7, 9, 14, and 16. UPD for these chromosomes has either been described in association with growth retardation or has been observed in confined placental mosaicism, a mechanism that may result in UPD. Maternal UPD7 was detected in three SRS patients, accounting for approximately 10% of the tested SRS patients. These results agree with previously published studies. The allelic distribution in one of the three families indicates complete isodisomy, whereas allelic patterns in the other two families are consistent with partial and complete heterodisomy, respectively, suggesting that, in the latter cases, UPD originates from maternal meiosis, whereas in the first case, it seems to be of mitotic origin. STR typing for UPD of chromosomes 2, 9, 14, and 16 showed no abnormalities. Our results demonstrate the necessity of screening SRS patients for UPD7, although the effect of UPD7 cannot be correlated with the SRS phenotype as yet. An association between UPD for the other investigated chromosomes and SRS seems to be negligible. Received: 13 February 1997 / Accepted: 13 May 1997     

Saliva of the graminivorous Theropithecus gelada lacks proline‐rich proteins and tannin‐binding capacity

Gelada baboons are the sole survivors of the genus Theropithecus and the only known graminivorous primates. They developed special adaptations to their diet such as high‐crowned teeth for processing hard and abrasive feed. The fine‐tuning of salivary protein composition might be another key mechanism that is used by species for adapting to the environment and competing with rivals for exploiting new ecological niches. In order to test whether gelada (graminivorous) and hamadryas baboons (omnivorous) differ in their salivary protein composition, we compared whole saliva samples of captive Theropithecus gelada and Papio hamadryas using gel electrophoresis and tannin‐binding assay. We hypothesized that the amount of proline‐rich salivary proteins with tannin‐binding capacity is higher in baboons consuming a feed with high dicot/monocot rations. Dicots produce tannins as a chemical defense system, discouraging animals from eating them. In contrast to dicots, monocots do not synthesize tannins. The presence of tannin‐binding proteins in saliva should effectively inactivate the dicot tannin‐based defense mechanism and increase the dietary breadth and/or the capability to switch between monocots and dicot leaves. The lack of such tannin‐binding proteins in saliva would indicate a narrow dietary spectrum more restricted to monocots. We found T. gelada to completely lack proline‐rich proteins (PRPs) and tannin‐binding capacity similar to a great variety of other grazing mammals. In contrast, P. hamadryas does possess PRPs with tannin‐binding activity. The findings support a growing body of evidence suggesting a high‐level specialization of T. gelada to grass diets. However, it remains unclear, whether loss of salivary tannin‐binding capacity drove the gelada into its narrow feeding niche, or whether this loss is the result of a long process of increased specialization. Thus, from an ecological point of view, T. gelada appears to be more vulnerable to environmental changes than other baboon species owing to its narrow dietary traits. Am. J. Primatol. 71:663–669, 2009. © 2009 Wiley‐Liss, Inc.