Thermodynamics of the charge recombination in photosystem II

The temperature dependence of the electric field-induced chlorophyll luminescence in photosystem II was studied in Tris-washed, osmotically swollen spinach chloroplasts (blebs). The system II reaction centers were brought in the state Z⁺P⁺-Q_A ^-Q_B ^- by preillumination and the charge recombination to the state Z⁺PQ_AQ_B ^- was measured at various temperatures and electrical field strengths. It was found that the activation enthalpy of this back reaction was 0.16 eV in the absence of an electrical field and diminished with increasing field strength. It is argued that this energy is the enthalpy difference between the states IQ_A ^- and I^-Q_A and accounts for about half of the free energy difference between these states. The redox state of Q_B does not influence this free energy difference within 150 s after the photoreduction of Q_A. The consequences for the interpretation of thermodynamic properties of Q_A are discussed.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea - I intermediary electron acceptor - Mops 3-(N-morpholino)propanesulphonic acid - P (P₆₈₀) primary electron donor - PS II photosystem II - Q_A and Q_B first and second quinone electron acceptors - Tricine N-tris(hydroxymethyl)methylglycine - Tris tris-(hydroxymethyl)aminomethane - Z secondary electron donor Dedicated to Professor L.N.M. Duysens on the occasion of his retirement     

Ontogeny of human fetal catalase superoxide dismutase and lipid peroxidation: A comparative study

A comparative study on the activity profile of catalase and superoxide dismutase, the two scavenging enzymes, as well as the developmental profile of lipid peroxidation in the human fetal brain, liver and kidney have been done for gestation periods ranging from 12 weeks to 28 weeks and beyond. The activity of the scavenging enzymes increase gradually in_all the tissues with the advancement of pregnancy. Brain is an exception in case of catalase where the activity remains more or less same throughout the developmental period except in the case of fetuses, 28 weeks and above where significant decrease in the catalase activity is observed. A high level of lipid peroxidation is observed during early stages of development which declines thereafter.     

IMP production and energy metabolism during exercise in rats in relation to age.

IMP production in and force exerted by rat quadriceps muscle in situ during various types of exercise were examined in relation to age. During continuous isometric exercise with constant stimulation time, the amount of IMP was linearly and inversely related to the age of the animals; a higher IMP concentration was found in intermittent isometric and dynamic exercise. No relationship was found between the total AMP deaminase activity and age. Exercise influenced neither the total activity nor the activity in the soluble fraction. From the results it is concluded that: the IMP concentration is linearly related to the free intracellular ATP4-/ADP3- ratio and the free AMP2- concentration; older animals are better able to maintain a high intramuscular ATP4-/ADP3- ratio and a low AMP2- concentration; IMP is produced in particular under conditions when the muscle has to work under extreme stress. IMP possibly exerts a feed-back control on the contraction system.     

Direct in vitro action of thyroid hormones on mitochondrial RNA-polymerase

The authors show the direct in vitro action of thyroid hormones on RNA-polymerase activity in rat liver mitochondria. 3,5,3 L-triiodothyronine (L-T₃) and 3,5,3,5 L-tetraiodothyronine (L-T₄) stimulate mitochondrial RNA synthesis without either increasing the permeability of preswollen mitochondria or stimulating the synthesis of the triphosphate ribonucleotides (NTP's). Thyroid hormones do not directly depress mitochondrial RNA hydrolysis. Studies carried out with structural analogues of thyroid hormones indicate the structural specifications of the regulating system of the mitochondrial RNA-polymerase. L-T₃ and L-T₄ are also effective in vitro on mitochondria obtained from animals undergoing different hormonal and dietary treatments, with the exceptions of those fed with a hypoprotein diet. Thus, the authors suggest the possible intervention of a specific mitochondrial receptor for L-T₃ and L-T₄.     

Isolation and structural studies on a galactofuranosyl-containing glycopeptide fromAscobolus furfuraceus

A galactofuranosyl-containing glycopeptide has been isolated from mycelium ofAscobolus furfuraceus by extraction with water. The glycoconjugate was purified by DEAE-cellulose chromatography followed by gel filtration. A molecular weight of about 20 000 was determined by the latter method using standard dextrans. Neutral sugars accounted for 94.5% of the glycopeptide and were characterized as mannose, galactose, and glucose. Glucosamine was estimated colorimetrically (1.8%). The molar ratio of Man:Gal:Glc:GlcNH₂ was 68:32:16:2. A trace amount of total phosphorus (0.2%) was found. The predominant amino acids were threonine and serine. The peptide moiety was labeled with [¹⁴C]formaldehyde and the elution of radioactivity was coincident with sugar on gel filtration in the presence of sodium dodecyl sulfate. The peak of radioactivity was retarded on release of galactose by mild acid hydrolysis. These results confirm the sugar-peptide linkage.     

The Alu I-induced bands in metaphase chromosomes of orangutan (Pongo pygmaeus)

Summary Restriction endonucleases have been recently proved to be active on fixed chromosomes, thus they are useful in chromatin structure studies. Within this class of enzymes, Alu I is able to detect the presence and localization of highly repetitive DNA sequences in human and in other mammalian and dipteran species. In this paper the pattern obtained on fixed metaphase chromosomes of orangutan (Pongo pygmaeus) by Alu I digestion and Giemsa staining is shown. The results are discussed in the light of the distribution, in this species, of the I–IV human satellite DNAs. It is also suggested that in Pongo some highly repetitive sequences, different from the major human satellites, are present.     

Establishment of mutant murine mammary carcinoma FM3A cell strains transformed with the herpes simplex virus type 2 thymidine kinase gene

To establish cell systems appropriate for investigating the mode of action of antiherpetic nucleoside analogues, mutant cell strains were constructed from murine mammary carcinoma FM3A cells, which were deficient in TK, but were transformed with a recombinant plasmid DNA containing the HSV-2 TK gene. The transformed cells incorporated the viral DNA, expressed viral TK activity and showed unusually high sensitivity to the cytostatic action of the antiherpetic nucleoside analogues ACV and IVDU, both of which were only weakly inhibitory to the growth of the parent cells. Curiously, the FM3A cell strains transformed with HSV-2 TK gene showed a higher sensitivity to ACV and IVDU than the previously established cell line transformed with HSV-1 TK gene. This contrasts with the inhibitory effects of ACV and IVDU on acute HSV infection, since HSV-2 infection is slightly or considerably less susceptible than HSV-1 infection to inhibition by ACV or IVDU, respectively.     

Finger-print patterns in parents of children with Down Syndrome

Finger-prints of the parents of thirty four Down children were compared with thirty four couples with two or more normal children without a family history of genetic problems. The parents with children affected by translocation Down Syndrome and those with mosaicism were excluded. A comparison of the figure distributions in each of the fingers of the two groups shows a different distribution. Parents of children affected by Down Syndrome occupy an intermediate position between the parents of normal children and the subjects affected by Down Syndrome. The total sum of values of A (arch), Lu (ulnar loop), Lt (radial loop) and W in each of the groups were also compared using a contingency table. A significant difference (p<0,05) was found between both groups. The differences are imputed to the variables A and L.     

Recommendations from the Consensus Conference on Hypertension in the Elderly.

Since 1978 there have been dramatic advances in the understanding of the pathophysiologic features of unstable angina pectoris and in the availability of new therapies of proven efficacy. Coronary artery spasm has been shown to be an important mechanism of acute myocardial ischemia in patients with unstable angina, and coronary thrombosis has been established as an early event in the development of acute myocardial infarction and, possibly, sudden death. Intravenous nitrates and oral calcium antagonists have been made available and are now widely used. Acetylsalicylic acid has been shown to be of benefit. Improved techniques of myocardial preservation and the introduction of percutaneous transluminal coronary angioplasty have modified the surgical management of coronary artery disease.