Thermal denaturation of calf thymus DNA: existence of a GC-richer fraction

In 2.5 x 10(-4)M EDTA buffer, the derivative melting curve of calf thymus DNA shows a major band at 47 degrees with a shoulder at about 54 degrees . The fraction of melting area of this shoulder is about 13%. For reconstituted polylysine-calf thymus DNA complexes, in addition to the melting of free DNA regions at about 50 degrees (T(m)) there is another melting at about 106 degrees (T(m)) of polylysine-bound regions. The melting band of the complex at T(m) is not symmetrical. As more polylysine is bound to DNA the melting amplitude is diminished greatly on the major band at 47 degrees but only slightly on the shoulder at 54 degrees . The insensitivity of this shoulder appears to result from the existence of a 13% fraction of calf thymus DNA containing 55% GC. It is not favorably bound by polylysine. It remains in the supernatant after centrifugation and melts at about 54-56 degrees . This conclusion is further supported by two facts: the reconstitution method provides a condition for selective binding of polylysine to AT-rich DNA, and it yields a fully symmetric melting band at T(m) for complexes of polylysine with homogeneous bacterial DNA such as the one from M. luteus.     

Growth rate stimulation of marine pseudomonads by thiosulfate

The oxidation of thiosulfate to tetrathionate exerts a definite growth rate stimulation in glucose, acetate, and yeast extract cultures of some marine pseudomonads. The failure to find this effect in earlier studies with terrestrial isolates may lie in the particular conditions used in the present experiments (constant pH, high ratio of thiosulfate to organic substrate) or in the different metabolic characteristics of the marine isolates.Contribution No. 3220 from the Woods Hole Oceanographic Institution.     

Human placental cathepsin B1. Isolation and some physical properties

A reproducible procedure for the isolation, from human placenta, of a cathepsin B1 in a homogeneous state, demonstrated by electrophoretic, ultracentrifugal and enzymic criteria, was carried out. The pH optimum was near pH5.5. The placental enzyme catalysed the release of acid-soluble u.v.-dense products from haemoglobin and myoglobin. It was inhibited by heavy metals and several compounds which react with the thiol groups. The optimum temperature was between 37° and 42°C. The molecular weight of the enzyme was calculated to be 24250.     

Intermittent cyclophosphamide in pemphigus vulgaris and bullous pemphigoid

Cyclophosphamide, given in widely spaced doses, was used in the treatment of a patient with pemphigus vulgaris and a patient with bullous pemphigoid. To our knowledge, this form of therapy has not previously been reported in these two diseases. The distinct advantages of the larger intermittent dose method of cyclophosphamide therapy over the more conventional daily dose regimen are discussed.     

ION-INDUCED ULTRASTRUCTURAL TRANSFORMATIONS IN ISOLATED MITOCHONDRIA : The Energized Uptake of Calcium

The energized uptake of low levels of Ca²⁺ in the presence and absence of phosphate by isolated rat liver mitochondria, and the perturbation effected by this activity on ultrastructural and metabolic parameters of mitochondria have been investigated. In the presence of phosphate, low levels of Ca²⁺ are taken up by mitochondria and result in various degrees of ultrastructural expansion of the inner mitochondrial compartment. This indicates that low levels of Ca²⁺ in the presence of phosphate, are accumulated in an osmotically active form into the water phase of the inner compartment. The first clearly observable quantitative increase in the volume of the inner compartment occurs after the accumulation of 100 nmoles Ca²⁺/mg protein. An accumulation of 150–200 nmoles Ca²⁺/mg protein, which is equivalent to the osmolar concentration of endogenous K⁺, is required to effect a doubling of the volume of the inner compartment. This degree of osmotic perturbation occurs as mitochondria transform from a condensed to an orthodox conformation. The osmotically induced orthodox conformation differs from the mechanochemically induced orthodox conformation previously described, in that its development is concomitant with a marked decrease in acceptor control and oxidative phosphorylation efficiency and it fails to transform to a condensed conformation in response to addition of ADP. In the absence of added phosphate, a maximum of 190 nmoles Ca²⁺/mg protein was found to be taken up by mitochondria (state 6). Ca²⁺ is apparently bound under state 6 conditions since the uptake does not effect an ultrastructural expansion of the inner compartment. Phosphate added after state 6 Ca²⁺ binding, however, results in an immediate ultrastructural expansion of the inner compartment. The addition of phosphate to mitochondria in the absence of exogenous Ca^2- fails to effect an osmotic ultrastructural transformation. Under state 6 conditions, the binding of between 40 and 190 nmoles Ca²⁺/mg protein results in the formation of dense matrix inclusions which appear to be composed of tightly packed, concentrically oriented membranes. Under conditions in which the bound Ca²⁺ is subsequently released, there is a concomitant loss in the density of these matrix inclusions, leaving behind morphologically distinct membrane whorls in the mitochondrial matrix.     

Alternate Requirement for Vitamin B12 or Methionine in Mutants of Pseudomonas denitrificans, a Vitamin B12-producing Bacterium

Experiments are described which indicate that Pseudomonas denitrificans, an organism that overproduces vitamin B(12), uses the B(12) pathway exclusively for methionine synthesis.     

Nitrogen chlorosis in blue-green algae

Summary Nitrogen deficient Anacystis nidulans contained normal levels of chlorophyll-a and carotenoids but did not contain any phycocyanin. These organisms also contained large amounts of polysaccharide. The addition of nitrate to a deficient culture resulted in the recovery of normal pigmentation over a period of several hours.The relation between these changes and growth was established by a kinetic study of the changes in cell composition during pigment loss and recovery. Loss of phycocyanin commenced with the cessation of growth due to nitrogen limitation and was complete after 15 hours. In contrast there were only minor changes in chlorophyll-a and carotenoid. After growth had ceased polysaccharide continued to increase and viability dropped sharply although total cell counts did not change. These trends were reversed by the addition of nitrate to deficient cultures. Phycocyanin was detected after a short lag and normal levels of phycobiliprotein were present within 8 hours. Cell division did not begin until normal levels of phycocyanin had been restored. During the recovery of normal pigmentation there was a decrease in reducing sugar content and a sharp rise in viability. Qualitative studies with 9 additional blue-green algae suggest that loss of phycocyanin is a characteristic feature of nitrogen deficiency in blue-green algae.