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A Weise

Publications and source records attributed to A Weise.

9 recordsLinked to original sources
PubMed2000

Function of the cytosolic N-terminus of sucrose transporter AtSUT2 in substrate affinity.

AtSUT2 was found to be a low-affinity sucrose transporter (K(M)=11.7 mM at pH 4). Chimeric proteins between AtSUT2 and the high-affinity StSUT1 were constructed in which the extended N-terminus and central loop of AtSUT2 were exchanged with those domains of StSUT1 and vice versa. Chimeras containing the N-terminus of AtSUT2 showed significantly lower affinity for sucrose compared to chimeras containing the N-terminus of StSUT1. The results indicate a significant function of the N-terminus but not the central cytoplasmic loop in determining substrate affinity. Expression of AtSUT2 in major veins of source leaves and in flowers is compatible with a role as a second low-affinity sucrose transporter or as a sucrose sensor.

Amino Acid Sequence↗
PubMed2000

SUT2, a putative sucrose sensor in sieve elements.

In leaves, sucrose uptake kinetics involve high- and low-affinity components. A family of low- and high-affinity sucrose transporters (SUT) was identified. SUT1 serves as a high-affinity transporter essential for phloem loading and long-distance transport in solanaceous species. SUT4 is a low-affinity transporter with an expression pattern overlapping that of SUT1. Both SUT1 and SUT4 localize to enucleate sieve elements of tomato. New sucrose transporter-like proteins, named SUT2, from tomato and Arabidopsis contain extended cytoplasmic domains, thus structurally resembling the yeast sugar sensors SNF3 and RGT2. Features common to these sensors are low codon bias, environment of the start codon, low expression, and lack of detectable transport activity. In contrast to LeSUT1, which is induced during the sink-to-source transition of leaves, SUT2 is more highly expressed in sink than in source leaves and is inducible by sucrose. LeSUT2 protein colocalizes with the low- and high-affinity sucrose transporters in sieve elements of tomato petioles, indicating that multiple SUT mRNAs or proteins travel from companion cells to enucleate sieve elements. The SUT2 gene maps on chromosome V of potato and is linked to a major quantitative trait locus for tuber starch content and yield. Thus, the putative sugar sensor identified colocalizes with two other sucrose transporters, differs from them in kinetic properties, and potentially regulates the relative activity of low- and high-affinity sucrose transport into sieve elements.

Amino Acid Sequence↗
PubMed2000

A new subfamily of sucrose transporters, SUT4, with low affinity/high capacity localized in enucleate sieve elements of plants.

A new subfamily of sucrose transporters from Arabidopsis (AtSUT4), tomato (LeSUT4), and potato (StSUT4) was isolated, demonstrating only 47% similarity to the previously characterized SUT1. SUT4 from two plant species conferred sucrose uptake activity when expressed in yeast. The K(m) for sucrose uptake by AtSUT4 of 11.6 +/- 0.6 mM was approximately 10-fold greater than for all other plant sucrose transporters characterized to date. An ortholog from potato had similar kinetic properties. Thus, SUT4 corresponds to the low-affinity/high-capacity saturable component of sucrose uptake found in leaves. In contrast to SUT1, SUT4 is expressed predominantly in minor veins in source leaves, where high-capacity sucrose transport is needed for phloem loading. In potato and tomato, SUT4 was immunolocalized specifically to enucleate sieve elements, indicating that like SUT1, macromolecular trafficking is required to transport the mRNA or the protein from companion cells through plasmodesmata into the sieve elements.

Amino Acid Sequence↗
PubMed1992

Prevalence of hepatitis C virus infections in dialysis patients and their contacts using a second generation enzymed-linked immunosorbent assay.

The prevalence of antibodies to the hepatitis C virus (HCV) was determined in 498 hemodialysis patients from three german dialysis units, 121 staff members and 42 family members using an enzyme-linked immunosorbent assay (ELISA) of the second generation which detects antibodies to a structural (C22) and to non-structural (C33c, C100, 5-1-1) recombinant antigens to HCV. Using the second generation ELISA 115 patients (23.1%) were anti-HCV positive versus 77 (15.5%) when sera were tested by an ELISA of the first generation containing only a non-structural antigen (C100). In 34 of these 40 discordant sera antibodies against at least one viral protein was found by a recombinant immunoblot assay. Of 5 sera containing antibodies to only one viral protein (C22) 3 were HCV RNA positive by polymerase chain reaction. Epidemiological evaluation of the patients revealed that the prevalence of anti-HCV was correlated to the duration of dialysis but not to the number of blood transfusions. Of 121 staff members 2 (1.6%) and 2 of 42 family members (4.7%) were positive indicating a low risk of the patients' contacts of acquiring HCV infection.

Adolescent↗
PubMed1982

Salivary secretion in reflux esophagitis.

It has been speculated that impaired salivary flow and contents contribute to abnormal acid clearance in patients with reflux esophagitis. To test this hypothesis, salivary secretion of volume, bicarbonate, and N-acetylneuraminic acid was measured in patients with reflux esophagitis, in age- and sex-matched controls, and in healthy young volunteers. Resting saliva was collected by permitting the saliva to drip into a flask every 30 s. Parotid saliva was collected by means of a Lashley capsule during stimulation by oral infusion of 1 ml/min of 2% citric acid. Total mixed saliva was collected by a dental sucker during esophageal perfusion with water and 10-mM hydrochloric acid. The volume of resting saliva and its concentration of bicarbonate were similar in the three groups. The concentration and the output of N-acetylneuraminic acid were higher in the young volunteers than in the two other groups. The volume flow and the composition of stimulated parotid saliva were similar in the three groups of subjects. Volume of total mixed saliva and concentration of bicarbonate and N-acetylneuraminic acid during esophageal perfusion with water were higher in patients with reflux esophagitis than in age- and sex-matched controls and were similar to the values found in young healthy volunteers. Acid perfusion increased the secreted volume of total mixed saliva by 150% and the concentration of bicarbonate by 30% in healthy young volunteers, but not in patients with reflux esophagitis and in the healthy age- and sex-matched controls; the concentration of N-acetylneuraminic acid was left unaffected by acid perfusion in all three groups. These findings disprove the hypothesis of impaired salivation in reflux esophagitis. The age-related loss of salivary response to acidic esophageal perfusion might be the reason why reflux esophagitis with peptic lesions affects predominantly elder people.

Adult↗