Cooperative interaction of reduced pyridine nucleotides with estrogen synthetase of human placental microsomes

The estrogen synthetase present in human placental microsomes appears to be dependent on the cooperative interaction of the reduced cofactors NADPH and NADH for optimal activity. Using steady-state concentrations of either cofactor, it was found that while the estrogen synthetase activity followed hyperbolic saturation kinetics with NADPH (K_mapp = 14 μM), the enzyme followed sigmoidal saturation kinetics when the cofactor was NADH, with the half-maximum velocity attained at a cofactor concentration of 1.1 mm. The maximum velocity obtained with NADPH as the cofactor was greater than with corresponding concentrations of NADH. Estrogen synthetase activity in the presence of NADH was not due to NADPH contamination. NADH, in the presence of small concentrations of NADPH (0.5 to 5 μm), stimulated significantly the rate of estrogen formation from androstenedione by placental microsomes and, in addition, the enzyme saturation kinetics changed from sigmoidal to hyperbolic, thus mimicking the effect of NADPH. Estrogen synthetase activity, measured in the presence of 1 mm NADH, was stimulated in a dose-dependent manner by NADPH (K_mapp = 0.4 μM NADPH) and, when the enzyme was measured in the presence of 5 μm NADPH, the activity was stimulated in a dose-dependent manner by NADH (K_mapp = 45 μM NADH). Estrogen synthetase activity measured in the presence of NADH, without and with NADPH (1 μm) remained linear both with time of incubation for approximately 15 min and with microsomal protein concentration up to 3 mg/ml. The apparent K_m of estrogen synthetase for androstenedione, when measured in the presence of NADH, was 1 μm. The synergistic interaction between NADH and NADPH in stimulating placental estrogen synthetase activity observed in vitro may, conceivably, take place in vivo in the intact placenta.     

The rise and fall of pineal N-acetyltransferase in vitro: Neural regulation in the developing rat

In rats, the pineal gland has a rhythm in the activity of the enzyme, N-acetyltransferase (NAT), which is thought responsible for daily cycles of melatonin synthesis. Neonatal rat pineal glands, but not those of adult rats, have a single cycle that is observed in vitro during the first day of organ culture. The neural regulation of the cycle was investigated using neonatal rats with adult rats used for comparison. Prior treatment of rat pups with constant light did not abolish the cycle in vitro though it did abolish the in vivo rhythm. Removal of the superior cervical ganglia did not abolish the in vivo rhythm that was measured the first day after surgery, but ablation of the ganglia did abolish the rhythm if several days or more elapsed after surgery. Extirpation of the superior cervical ganglia abolished the in vitro NAT cycle in pup pineal glands as did the pharmacological equivalent, injection of 6-hydroxydopamine. Propranolol, a beta blocking agent, prevented the occurrence of the cycle in vitro.     

Angiotensin II potentiates responses of the rabbit basilar artery to adrenergic nerve stimulation

Angiotensin II has little contractile effect on the isolated rabbit basilar artery; however, it markedly potentiates contractile responses to adrenergic nerve stimulation. This is not a post-synaptic effect of angiotensin, as responses to exogenous norepinephrine are not altered. Angiotensin increases stimulation-evoked release of norepinephrine, and this effect probably accounts for the increased response to adrenergic nerve stimulation. Since sympathetic stimulation may protect the cerebral circulation from hypertensive damage, increased responsiveness to adrenergic nerve activity produced by angiotensin may have a beneficial effect.     

An ultrastructural search for lectin-binding sites on surfaces of spinach leaf organelles

Organelles isolated from leaves of spinach (Spinacia oleracea L.) were prefixed in glutaraldehyde and then incubated with ferritin conjugates of four lectins — Concanavalin A (Con A), Ricinus communis L. agglutinin, MW 120,000 (RCA), soybean agglutinin (SBA), and wheat germ agglutinin (WGA) — in order to probe their cytoplasmic surfaces for saccharide residues. In each case the major leaf organelles, including microbodies, mitochondria and chloroplast derivatives, failed to exhibit labeling when examined with the electron microscope. Tobacco (Nicotiana tabacum L.) leaf protoplasts, incubated simultaneously with and under identical conditions to the spinach organelles, showed specific labeling of their plasma membranes with all four lectin conjugates, thus establishing the efficacy of the procedure for demonstrating the presence of binding sites when they exist. Further attempts to show binding of one of the lectins, Con A, by labeling with fluorescein-Con A and by organelle agglutination, yielded results consistent with the absence of ultrastructural labeling. It is concluded that no saccharide residues recognized by the four lectins are present on the cytoplasmic surfaces of organelles and that those residues reported to be constituents of intracellular membranes, therefore, are most likely exposed on the luminal (extracytoplasmic) surfaces.Abbreviations Con A Concanavalin A - RCA Ricinus communis agglutinin, MW 120,000 - SBA soybean agglutinin - WGA wheat germ agglutinin     

The role of dietary fibre in the human colon.

Several effects of dietary fibre on colonic function have been documented by experiment or deduced from epidemiologic observation. The magnitude of these changes depends on the source and the physical and chemical composition of the fibre used, and on the individual response of the subjects. Three theories of the mode of action of fibre are discussed; they relate to the water-holding capacity of fibre, the production of short-chain fatty acids from fibre in the colon and the alteration by fibre of the colonic microflora.     

DNA and protein content of mouse sperm: Implications regarding sperm chromatin structure

A variety of biochemical and histochemical techniques have been used to compare the composition of chromatin in sperm nuclei isolated from the epididymides of five mouse strains. The DNA content was determined by phosphorus analysis, deoxyribose analysis, absorption spectroscopy at 260 nm, and cytomorphometry following gallocyanine chrome alum staining. All four methods indicate that the mouse sperm nucleus contains approx. 3.3 pg DNA and that the DNA content does not vary significantly among the strains tested. Three different techniques, quantitative amino acid analysis, absorption spectroscopy at 230 nm, and sperm head density analysis in cesium chloride, were used to determine the protein content. Sperm nuclei from each strain of mouse were found to have a protein to DNA ratio of 0.9 and a chromatin protein content of 3 pg/nucleus. Comparisons of the basic proteins by disc gel electrophoresis demonstrate that the sperm nuclei contain only protamine and lack significant levels of somatic histones or transition proteins. The sperm from each strain contained both mouse protamine variants and the relative distribution of the two proteins did not appear to differ among strains. Using this information, we have been able to draw certain conclusions regarding DNA-protamine interactions and the mode of DNA packaging in the sperm nucleus. The most important of these is that the DNA in the mouse sperm nucleus cannot be packaged in nucleosomes. The protamines in sperm chromatin do not function as structural proteins, providing a subunit core around which the DNA is wrapped, but appear to completely neutralize the phosphodiester backbone of the DNA molecule, thereby minimizing the repulsion between neighboring segments of DNA and allowing it to be condensed into a biochemically inactive particle of genetic information.     

Isolation of SPO12–1 and SPO13–1 from a Natural Variant of Yeast That Undergoes a Single Meiotic Division

ATCC4117 is a strain of S. cerevisiae that undergoes a single nuclear division during sporulation to produce asci containing two diploid ascospores (Grewal and Miller 1972). All clones derived from these spores are sporulation-capable and, like the parental strain, form two-spored asci. In this paper, we describe the genetic analysis of ATCC4117. In tetraploid hybrids of vegetative cells of the ATCC4117 diploid and a/a or α/α diploids, the production of two-spored asci is recessive. From these tetraploids, we have isolated two recessive alleles, designated spo12–1 and spo13–1, each of which alone results in the production of asci with two diploid or near-diploid spores. These alleles are unlinked and segregate as single nuclear genes. spo12–1 is approximately 22 cM from its centromere; spo13–1 has been localized to within 1 cM of arg4 on chromosome VIII. This analysis also revealed that ATCC4117 carries a diploidization gene allelic to or closely linked to HO, modifiers that reduce the number of haploid spores per ascus and alleles affecting the total level of sporulation.     

Mechanisms of spacing in groups of juncos: Measurement of behavioural tendencies in social situations

To investigate behavioural mechanisms that regulate the spacing of individuals, we studied aggression, approach, and avoidance of captive male juncos (Junco hyemalis) in relation to the distance between individuals. We measured behavioural tendencies by analysing the terminations of social states so as to determine the instantaneous probability rates of terminal actions. These rates permit accurate comparisons of behavioural tendencies in different social situations. An individual's tendencies to supplant, approach, or withdraw from an opponent depended on the dominance relationship of the two birds and on the distance between them. Interactions did not vary with the magnitude of the difference between opponents' ranks. The dependence of aggression, approach, and avoidance on the distance between opponents controls the spacing of individuals.