Alterations in the phospholipid composition of Nocardia polychromogenes during growth.

The major phospholipid classes of Nocardia polychromogenes were quantitated at different stages of the growth cycle. Significant differences were observed both in the total lipid phosphorus per g (dry weight) of cells, and in the relative percentages of individual phospholipids. The total amount of lipid-phosphorus increased throughout the growth cycle. Cardiolipin and phosphoinositides contents increased with significant decrease in phosphatidyl ethanolamine and unknown phospholipids.     

Distribution of calcitonin cells in the thyroid glands of normal adult rhesus monkey Macaca mulatta.

The calcitonin cells of adult rhesus monkey Macaca mulatta are located in the central region of thyroid along the median axis. The anterior and posterior poles, the isthmus and peripheral regions of thyroid are completely devoid of C cells. The parathyroid also lacks C cells.     

Cardiac-type excitation-contraction coupling in dysgenic skeletal muscle injected with cardiac dihydropyridine receptor cDNA

There are dihydropyridine (DHP)-sensitive calcium currents in both skeletal and cardiac muscle cells, although the properties of these currents are very different in the two cell types (for simplicity, we refer to currents in both tissues as L-type). The mechanisms of depolarization-contraction coupling also differ. As the predominant voltage-dependent calcium current of cardiac cells, the L-type current represents a major pathway for entry of extracellular calcium. This entry triggers the subsequent large release of calcium from the sarcoplasmic reticulum (SR). In contrast, depolarization of skeletal muscle releases calcium from the SR without the requirement for entry of extracellular calcium through L-type calcium channels. To investigate the molecular basis for these differences in calcium currents and in excitation-contraction (E-C) coupling, we expressed complementary DNAs for the DHP receptors from skeletal and cardiac muscle in dysgenic skeletal muscle. We compared the properties of the L-type channels produced and showed that expression of a cardiac calcium channel in skeletal muscle cells results in E-C coupling resembling that of cardiac muscle.     

The AA and ANA rat lines, selected for differences in voluntary alcohol consumption

The offspring of rats that voluntarily select larger quantities of alcohol are heavier consumers of alcohol than the offspring of rats that tend to avoid it. Such selective breeding, repeated over many generations, was used to develop the AA (Alko, Alcohol) line of rats which prefer 10% alcohol to water, and the ANA (Alko, Non-Alcohol) line of rats which choose water to the virtual exclusion of alcohol. In addition to demonstrating the likely role of genetic factors in alcohol consumption, these lines have been used to find behavioral, metabolic, and neurochemical correlates of differential alcohol intake. Some of the line differences that have been found involve the reinforcing effects of ethanol, the changes in consumption produced by alcohol deprivation and nutritional factors, the behavioral and adrenal monoamine reactions to mild stress, the development of tolerance, the accumulation of acetaldehyde during ethanol metabolism, and the brain levels of serotonin. It is hoped that these studies will lead to a better understanding of the genetically-determined mechanisms that influence the selection of alcohol.     

Suppression of c-ras transformation by GTPase-activating protein

The ras genes are required for normal cell growth and mediate transformation by oncogenes encoding protein tyrosine kinases. Normal ras can transform cells in vitro and in vivo, but mutationally activated ras does so much more efficiently, and highly transforming mutant versions of ras have been isolated from a variety of human and animal tumours. The ras genes encode membrane-associated, guanine nucleotide-binding proteins that are active when GTP is bound and inactive when GDP is bound. The slow intrinsic GTPase activity of normal mammalian Ras proteins can be greatly accelerated by the GTPase-activating protein (GAP), which is predominantly cytoplasmic. This activity of GAP, which can increase with cell density in contact-inhibited cells, suggests that it functions as a negative, upstream regulator of ras. Other studies, however, show that GAP interacts with a region of ras-encoded protein implicated in ras effector function, which raises the possibility that GAP might also be a downstream target of ras. Mutationally activated ras-encoded proteins also interact with GAP, although they are resistant to its catalytic activity. In an attempt to define the role of GAP in ras-mediated transformation, we examined the effects on transformation of normal or mutant ras when cells overexpress GAP. We found that GAP suppresses transformation of NIH 3T3 cells by normal Ha-ras (c-ras) but does not inhibit transformation by activated Ha-ras (v-ras). These results support the hypothesis that GAP functions as a negative regulator of normal ras and make it unlikely that GAP alone is the ras target.     

Latent iron deficiency alters gamma-aminobutyric acid and glutamate metabolism in rat brain

Summary A diet containing 18–20 mg iron/kg to young weaned rats for 8 weeks altered the metabolism of gamma-aminobutyric acid and glutamate in the central nervous system without affecting blood hemoglobin. Subsequent rehabilitation with 390 mg iron/kg diet for 2 weeks normalized these changes.     

Substrate specificity and affinity of a protein modulated by bound water molecules

Water molecules influence molecular interactions in all biological systems, yet it is extremely difficult to understand their effects in precise atomic detail. Here we present evidence, based on highly refined atomic structures of the complexes of the L-arabinose-binding protein with L-arabinose, D-fucose and D-galactose, that bound water molecules, coupled with localized conformational changes, can govern substrate specificity and affinity. The atoms common to the three sugars are identically positioned in the binding site and the same nine strong hydrogen bonds are formed in all three complexes. Two hydrogen-bonded water molecules in the site contribute further to tight binding of L-arabinose but create an unfavourable interaction with the methyl group of D-fucose. Equally tight binding of D-galactose is attained by the replacement of one of the hydrogen-bonded water molecules by its--CH2OH group, coordinated with localized structural changes which include a shift and redirection of the hydrogen-bonding interactions of the other water molecule. These observations illustrate how ordered water molecules can contribute directly to the properties of proteins by influencing their interaction with ligands.     

The colour centre in the cerebral cortex of man

Anatomical and physiological studies have shown that there is an area specialized for the processing of colour (area V4) in the prestriate cortex of macaque monkey brain. Earlier this century, suggestive clinical evidence for a colour centre in the brain of man was dismissed because of the association of other visual defects with the defects in colour vision. However, since the demonstration of functional specialization in the macaque cortex, the question of a colour centre in man has been reinvestigated, based on patients with similar lesions in the visual cortex. In order to study the colour centre in normal human subjects, we used the technique of positron emission tomography (PET), which measures increases in blood flow resulting from increased activity in the cerebral cortex. A comparison of the results of PET scans of subjects viewing multi-coloured and black-and-white displays has identified a region of normal human cerebral cortex specialized for colour vision.     

Nature of the FeO2 bonding in myoglobin: an overview from physical to clinical biochemistry

The iron(II)-dioxygen bond in myoglobin and hemoglobin is a subject of wide interest. Studies range from examinations of physical-chemical properties dependent on electronic structure, to investigations of stability as a function of oxygen supply. Stability properties are of particular importance in vivo, since the oxygenated form is known to be oxidized easily to the ferric form, which cannot be oxygenated and is therefore physiologically inactive. Kinetic and thermodynamic studies of the stability of native oxymyoglobin have revealed a new feature in FeO2 bonding. In vivo, the iron center is always subject to a nucleophilic attack of the water molecule or hydroxyl ion, which can enter the heme pocket from the surrounding solvent, and thereby irreversibly displace the bound dioxygen from MbO2 in the form of O2- so that the iron is converted to the ferric form. A free energy diagram for the potential reactions of FeO2 visualizes myoglobin as a molecular structure that can provide in solution the delicate balance of kinetic and thermodynamic factors necessary to stabilize reversible oxygenation, as opposed to irreversible autoxidation to metmyoglobin.