Genetic definition of a further gene region and identification of at least three different histocompatibility genes in the rat major histocompatibility system

Two new recombinant haplotypes of the rat major histocompatibility system,RT1, have been detected in [LEW.1A (RT1 ^a ) ×LEW.1W (RT1 ^u )] × LEW 1N(RT1 ⁿ ) segregating hybrids. Recombinantr3 carries theRTL1. A region (determining classical transplantation antigens) and theRT1.B region (determining strong mixed lymphocyte reactivity and genetic control of antipolypeptide immune responsiveness) of the RT1^a parent, bur rejects RT1^a skin grafts. Recombinantr4 carries theA andB regions of the RT1^u parent, but rejects RT1^u skin grafts. The two histocompatibility genes detected are allelic to each other. The relevant locus, designated asH-C, maps to theB-region side of theRT1 system and appears to mark a thirdRT1 gene region,RT1.C. Availability of haplotypes r3 andr4 allowed the definition of a histocompatibility locus in theB region,H-B. The products ofH-C, H-B and of the previously describedH-A gene vary in antigenic strength.     

Enzymatic synthesis of β-lactam antibiotics: A thermodynamic background

The equilibrium constants and the respective standard Gibbs energy changes for hydrolysis of some β-lactam antibiotics have been determined. Native and immobilized penicillin amidase (EC 3.5.1.11) from Escherichia coli has been used as a catalyst. The values of standard Gibbs energy changes corresponding to the pH-independent product of equilibrium concentrations (ΔG⁰_c = ? RT ln K_c) have been calculated. The differences in the structure of the antibiotics nucleus hardly ever affect the value of the pH-independent component of the standard Gibbs energy change (ΔG⁰_c) and value of apparent standard Gibbs energy change at a fixed pH (ΔG^0′_c). At the same time, the value of ΔG⁰_c is more sensitive to the structure of the acyl moiety of the antibiotic; when ampicillin is used instead of benzylpenicillin, ΔG⁰_c increases by ～6.3 kJ mol^?1 (1.5 kcal mol^?1). pH-dependences of the apparent standard Gibbs energy changes for hydrolysis of β-lactam antibiotics have been calculated. The pH-dependences of ΔG^0′_c for hydrolysis of all β-lactam antibiotics have a similar pattern. The thermodynamic pH optimum of the synthesis of these compounds is in the acid pH range (pH < 5.0). The breakage of the β-lactam ring leads to a sharp decrease in the ΔG^0′_c value and a change in the pattern of the pH-dependence. For example, at pH 5.0 ΔG^0′_c decreases from 14.4 kJ mol^?1 for benzylpenicillin to ?1.45 kJ mol^?1 for benzylpenicilloic acid. The reason for these changes is mainly a considerable increase in the pK of the amino group of the nucleus of the antibiotic and, as a consequence, a decrease in the component of standard Gibbs energy change, corresponding to the ionization of the system. The thermodynamic potentials of the enzymatic synthesis of semisynthetic penicillins and cephalosporins on the basis of both free acids and their derivatives (N-acylated amino acids, esters) are discussed. It is shown that with esters of the acids, a high yield of the antibiotic can, in principle, be achieved at higher pH values.     

The role of endogenous cytokinins in correlation between cotyledon and its axillary bud and in hypocotyl regeneration of flax

When flax seedlings are decapitated above cotyledons and three days later one of the two cotyledons is removed then the remaining cotyledon stimulates in four to five days growth of its axillary bud. It has been found that content of endogenous cytokinins was higher in the stimulated bud as compared with the other one already 12 h after the cotyledon removal. Flax seedlings decapitated under cotyledons regenerate adventitious buds on thy hypocotyl stump during 5–6 days. The endogenous fytohormonal preparation of this regeneration was investigated in the 20 mm apical part of the hypocotyl stump. Decrease in auxin and increase in gibberellins was already found during the first day after decapitation while the level of cytokinins increased as late as three days after the apex removal.     

Genetic determination of the mitochondrial adenine nucleotide translocation system and ITS role in the eukaryotic cell

On integrating experimental data published previously, the following picture of the mitochondrial adenine nucleotide (AdN) translocation system is being presented: 1. The AdN translocation system serves not only to transport ATP synthesized within mitochondria into the cytosol but also to transport cytosolic ATP into the mitochondria when oxidative phosphorylation is not functioning. 2. The AdN translocator is coded for by nuclear genes and the mitochondrial protein synthesis is not involved in its formation. 3. The AdN translocation system must be preserved and functioning even in cells which could dispense with oxidative phosphorylation. It assures appropriate concentrations of intramitochondrial ATP. 4. The intramitochondrial ATP is required for normal replication of mitochondrial DNA. Tis supports the view that the mitochondrion is a self-replicating semi-autonomous organelle. 5. The appropriate concentration of ATP must be present in mitochondria to make possible cell growth or multiplication. This points to a direct or indirect role of mitochondria in the control of cell proliferation.     

Age-related changes in chromatin of liver cell nuclei of different ploidity

Summary A comparsion of the Feulgen hydrolysis curves and the chromatin compactness of the liver cell nuclei of young and old rats was made. It was found that the rate of DNA depurination and chromatin compactness are higher in the liver cell nuclei of old rats, both in di-and tetraploidal cells. The effect of fixation upon the course of the hydrolysis curves is discussed.This investigation was supported by grant 474/VI Committee of Cell Pathology, Polish Academy of Sciences     

The effect of phosphatidylcholine depletion on biochemical and physical properties of a Neurospora crassa membrane mutant

By using the choline starvation process it is possible to deplete the membranes of Neurospora crassa choline auxotroph $\text{chol-1}$ of phosphatidylcholine, without affecting the viability of germinated spores or whole mycelium. Spin label probes were used to examine the possible dependence of the physical state of cellular lipids on the presence of phosphatidylcholine in the membranes.Increased freedom of rotational motion of lipid soluble probes was regularly detected in choline-starved mycelium. The accumulation of neutral lipids (mostly triglycerides) in bulk form was also observed during the choline starvation process. The experiments with isolated and separated lipid classes indicated that the observed increase in fluidity of lipids in choline-starved mycelium is partly due to the difference in physical properties between bulk lipids and membrane lipids. Spin label probe 2N4 ($\text{2-}\text{propyl}\text{-2,5,5-}\text{trimethyl-oxazolidine}\text{-N-}\text{oxyl}$), which can partition at the membrane-water interface, exhibited easier partitioning among membrane lipids of choline-starved mycelium.     

The effect of sodium on depolarization-induced calcium uptake and acetylcholine release by synaptosomes

The influence of external sodium concentration on potassium (depolarizing agent)-stimulated calcium uptake and Ca⁺-dependent acetylcholine release by rat cerebral cortex synaptosomes has been studied. It was found that increased sodium concentration decreases both the Ca²⁺ uptake and the acetylcholine release, whereas a low external sodium concentration is stimulatory.     

Effect of N-Methyl Substituents in 2-Methoxycarbonylphenylsulfamides on Kinetics and Mechanism of Formation of (1H)-2,1,3-Benzothiadiazin-4(3H)-One-2,2-Dioxides

The cyclization reactions of N-methyl-N’-(2-methoxycarbonylphenyl)sulfamide (1a), N-methyl-N-(2-methoxycarbonylphenyl)-sulfamide (2a), and 2-methoxycarbonylphenylsulfamide (3a) were studied in aqueous amine buffers (butylamine, ethanolamine, morpholine, glycinamide). The dependences observed between the rate constants and buffer concentrations show that the reactions are subject to base catalysis in all the three cases, the decomposition of the tetrahedral intermediate being rate limiting. The ratio of the relative rate constants of the base catalyzed cyclizations reactions of the three derivatives is 1a: 2a: 3a = 1: 20000: 100. The logarithm of rate constants of the base catalyzed cyclization reactions was plotted against the pK_a values of conjugated acids of the individual amines used as the buffers in the cyclization of compound 1a, and the value of the Brönsted coefficient obtained was about 0.1, which means that the proton transfer from the intermediate to the basic buffer component is thermodynamically favorable. The intermediate is a much weaker base, and the reaction is controlled by diffusion. The slope of an analogous dependence for compound 2a gradually decreases from values near to 0.5 to values near to zero, which means that the intermediate formed from compound 2a (pK_a ≈ 9.3) has a pK_a value comparable with that of the acid buffer component.