Studies on the reaction mechanism of a ribonuclease II from Aspergillus oryzae (author's transl)]

Ribonuclease T2 was isolated from an Aspergillus oryzae extract. In order to define the substrate specificity, the hydrolysis of a series of 2',3'-cyclic nucleotides was measured semiquantitatively. Modifications in all positions of the bases are tolerated, as long as the base stays in the anti conformation or has a chance to return to it; bulky substituents at N-3 of the pyrimidine base lower the rate. So far the conclusion seems justified that the enzyme does not react with the substrates by specific bonds to the base, but rather by hydrophobic binding. The conformation specificity and the pH dependence of the activity support this hypothesis. The pH optima with substrates which may be positively or negatively charged are shifted to pH values at which the substrates are uncharged. This strongly indicates a hydrophobic type of interaction between base and enzyme. From the pH dependence of the kinetic parameters Km and k+2, an enzyme group with a pK of 7 (probably histidine) can be postulated. This group should interact in the protonated form with the phosphate anion. Another B.HB-system (probably two carboxylate groups) seems to be involved in the catalysis step, performing the base catalysis at the 2'-OH group and the proton catalysis at the phosphate oxygen simultaneously.     

Stimulation of cytokine and nitric oxide production by acyclic nucleoside phosphonates.

Several antiviral acyclic nucleotide analogues activate expression of genes for cytokines, such as TNF-alpha, IL-10 in macrophages and IFN-gamma in splenocytes. This is an underlying mechanism for substantially enhanced production of nitric oxide generated by IFN-gamma. More lipophilic prodrugs, bis-POM-PMEA and bis-POC-PMPA, are cytocidal for macrophages and thus inhibit nitric oxide formation.     

Strain typing in the genus Lactobacillus

1. Introduction, 63
2. Techniques used for strain typing in the genus Lactobacillus , 63
3. Applications of strain typing in the genus Lactobacillus , 64,
4. Future prospects, 65
5. References, 65     

Metabolic phosphorylation and excretion of some nucleoside analogues in insects

After oral administration to the hemipteran insect Pyrrhocoris apterus L. (Fireburg), the L-enantiomers and certain open-chain analogues of the nucleosides are rapidly converted into the corresponding monophosphates, which are then excreted. This metabolic phosphorylation is almost quantitative; it occurs at the primary as well as at the secondary hydroxylic groups. The process is abolished when the respective nucleoside analogues contain a free carboxylic group. By contrast, the phosphorylating capacity is unaffected by structural variations at the heterocyclic base. This phosphorylation and excretion may represent a part of detoxication mechanism for the above nucleoside analogues.     

Interactions of calf spleen purine nucleoside phosphorylase with antiviral acyclic nucleoside phosphonate inhibitors: kinetics and emission studies.

Association between calf spleen purine nucleoside phosphorylase and a series of phosphonylalkoxyalkyl derivatives of purine bases was studied by inhibition kinetics and fluorimetric titrations. Dissociation constants, determined by fluorimetric titration in phosphate-free conditions, were lower than inhibition constants in 1 mM phosphate, and inhibition was still weaker in 50 mM phosphate, in accord with the postulated bisubstrate analogue character of this class of inhibitors.     

Mechanical integration of muscle, tegument, and subtegumental tissues by anchoring fibrils and microfibrils in the cestode Hymenolepis diminuta

Electron microscopic examination of the epidermal basement membrane region of the rat tapeworm, Hymenolepis diminuta, has revealed specialized connective tissue structures that appear to anchor the epidermis, or tegument, to the parenchymal tissues of the helminth, as well as interconnect subtegumental muscle fibers, tegument, and parenchyma. Anchoring fibrils-cross-banded bundles of ca. 3 nm diameter filaments--were observed to directly interlink tegument and muscle, muscle and muscle, and tegument, muscle, and parenchymal connective tissue. Anchoring fibrils therefore appear to mechanically integrate epidermal tissue movements in response to subtegumental muscle contraction. A well-developed stratum of microfibrils, forming the lamina reticularis of the tegumental basement membrane, may also help anchor the tegument as well as to serve as a flexible, reinforcing sheath that protects parenchymal tissues from excessive radial displacement due to muscle contraction.     

The effect of folate binding protein on the colony-forming activity of GM-CFC cells in vitro

A modified method for the preparation of specific folate binding protein was described. The GM-CFC stimulating activity of this SFBP preparation was investigated on tissue cultures of human bone marrow cells. It has been found that in the presence of HPCM the cell proliferation was markedly increased by the SFBP. In the absence of HPCM, however, the cell proliferation has been influenced either positively or negatively presumably in dependence on the expression of folate receptors on the GM-CFC bone marrow cells.