Sucrose transport into vacuoles isolated from barley mesophyll protoplasts

Sucrose transport has been investigated in vacuoles isolated from barley mesophyll protoplasts. Rates of sucrose transfer across the tonoplast were even higher in vitro than in vivo indicating that the sucrose transport system had not suffered damage during isolation of the vacuoles. Sucrose transport is carrier-mediated as shown by substrate saturation of transport and sensitivity to a metabolic inhibitor and to competitive substrates. A number of sugars, in particular maltose and raffinose, decreased uptake of sucrose. Sorbitol was slowly taken up but had no effect on sucrose transport. The SH-reagent p-chloromercuribenzene sulfonate inhibited sucrose uptake completely. The apparent K_m of the carrier for sucrose uptake was 21 mM. Transport was neither influenced by ATP and pyrophosphate, with or without Mg²⁺ present, nor by protonophores and valinomycin (with K⁺ present). Apparently uptake was not energy dependent. Efflux experiments with preloaded vacuoles indicated that sucrose unloading from the isolated vavuoles is mediated by the same carrier which catalyses uptake. The vacuole of mesophyll cells appears to represent an intermediary storage compartment. Uptake of photosynthetic products into the vacuole during the light apparently minimizes osmotic swelling of the small cytosolic compartment of vacuolated leaf cells when photosynthetic productivity exceeds the capacity of the phloem for translocation of sugars.Abbreviations Hepes 4-(2-hydroxyethyl)-1-piperazincethane-sulfonic acid - pCMBS p-chloromercuribenzene sulfonate Dedicated to Professor Dr. W. Simonis on the occasion of his 75th birthday     

Ionic inhibition of catalytic phosphorylation of histone by bovine brain protein kinase.

The effects of various ions commonly found in protein kinase assays upon the rate of histone phosphorylation catalyzed by the highly purified bovine brain enzyme, protein kinase I, have been investigated. Sodium, potassium, and magnesium were found to inhibit histone phosphorylation by protein kinase I in a similar manner. The degree of inhibition by any of these cations was demonstrated to be directly proportional to the square root of the ionic strength of the assay medium. The relationship between the ionic strength of the assay medium and the rate of histone phosphorylation catalyzed by protein kinase I was employed to correct the rate of histone phosphorylation at various magnesium acetate concentrations to a standard ionic strength. When this was done an analysis of the previously postulated rate law for histone phosphorylation c atalyzed by protein kinase I gave a binding constant for the magnesium-ATP complex which was in agreement with that expected for this complex on the basis of various binding constants available in the literature. These results demonstrate that it is unnecessary to postulate a specific ion inhibition process for protein kinase I by the ions employed in this study. They also support the reasonable assumption that magnesium ion binds to ATP at or prior to the rate-determining step in histone phosphorylation catalyzed by protein kinase I. The expression developed in this paper for the effect of ionic strength upon protein kinase I activity can now be used to correct activity measurements made under various assay conditions to a standard assay state, allowing facile comparisons of kinetic data. It should be possible to develop similar expressions for other protein kinases and substrates to permit useful interpretation of kinetic data.     

Relationships between the physical and genetic maps of a 470 x 10(3) base-pair region around the terminus of Escherichia coli K12 DNA replication

The physical map of the region on both sides of the terminus of Escherichia coli K12 DNA replication (Bouché, 1982) has been related to the following genetic markers: attφ80, trpABCDE, fnr, rac, trg and man. There are 46 kb² per minute between ftrp and man, indicating that conjugative transfer is not slowed down in the region of the terminus. Using this relationship, trg has been mapped to 31.4 minutes and rac was found to extend from 29.6 to 30.1 minutes. The third λ-homologous genetic element of E. coli K12 (Kaiser, 1980), to be called kim, was identified on the map at 34.2 to 34.6 minutes. The specific activities of fragments labeled at the end of a synchronized replication cycle have been measured. They indicate that, for the trp:: Mu strain studied, the ultimately labeled DNA is at 31.2 ± 0.2 minutes. DNA replication may be delayed or slowed down in a region extending 50 kb on either side of this position.     

Effects of disalicylidenepropanediamines on photosynthetic electron transport of isolated spinach chloroplasts

The effects of disalicylidenepropanediamine (DSPD) and disulfo-disalicylidenepropanediamine (sulfo-DSPD) on the photosynthetic electron transport of isolated chloroplasts have been reexamined.     

Cytophotometric Evidence of Non-S-Phase Extra-Dna In Human Neuronal Nuclei

After Feulgen staining with acriflavine-Schiff, the DNA content of glial and neuronal nuclei from various sites of the human CNS (pre- and post-central gyrus, cerebellar cortex and spinal cord) were determined by fluorescence cytophotometry. the specimens were obtained from twelve adult human autopsy cases. Glial cell nuclei always revealed a biomodal DNA distribution pattern with a large 2c and a smaller 4c peak. the 4c peak was most prominent in the cerebellum. A few 8c glial nuclei were found. Neuronal cell nuclei disclosed unimodal DNA histograms with hyperdiploid means in the range 2.2–2.5c (1.8–2.9c for the individual populations). Tetraploid 4c DNA values were not observed, neither in Purkinje cells, nor in pyramidal cells. In eleven out of a total of forty-four slides the higher DNA means of neuronal nuclei were found to be statistically significant (P < 0.05) when compared with a population of 2c hepatocytes on the same slide. The results indicate the existence of some ‘extra DNA’ in human neuronal cell nuclei, the biological significance of which has still to be elucidated. It is however, suggested that it may play an important role in the functional activity of the CNS.     

Über eine als Gastropodenlaich gedeutete Eiablage in einer Schale vonPseudopecten aus dem Lias von Salzgitter

An internal impression of the right valve of Pseudopecten aequivalvis (Sow.) from the Domerium layer (= Lias δ) at a discontinued iron-ore surface mine, Haverlahwiese near Salzgitter, contains bowl-shaped structures which may be interpreted as gastropod spawn. These are compared with similarly formed half-spheres of recent gastropod eggs which are laid on the inner side of a pecten shell.     

Heterogeneity of LSD-displacing factors and multiple types of high affinity LSD-binding sites

Heterogeneity of high affinity LSD-binding sites was confirmed by displacement studies with 2-bromo (+)—LSD and with apamin, a peptide neurotoxin. In line with the concept of multiple binding sites, a number of fractions of putative endogenous ligands could be separated from rat brain extract. The LSD-displacing β-fraction was not detectable in tissues lacking high affinity LSD-binding sites. High affinity dopamine- and serotonin-binding was differentially affected by the β-fraction.