A potent new dipeptide inhibitor of cell sickling and haemoglobin S gelation.

A dipeptide L-lysine-L-phenylalanine is shown to inhibit both cell sickling and the gelation of solutions of sickle-cell haemoglobin. The effect on deoxyhaemoglobin solutions and gels was followed by centrifugation; a progressive inhibition of gelation was observed up to 30 mM Lys-Phe. The haemoglobin concentration at the plateau (26 g/dl) suggests that an effect might be seen in vivo if suitable concentrations of Lys-Phe (about 20 mM) can be maintained in the blood stream. Additional studies of lag time before onset of gelation support this. Oxygen dissociation curves of sickle cells showed an effect of Lys-Phe only after incubation for 3 h before measurement, the P50 decreasing from 51 mmHg (6.8 MPa) to 41 mmHg (5.5 MPa) for cells depleted of 2,3-bisphosphoglycerate. The effect of Lys-Phe on intact sickle cells was more rapid. A marked increase in the number of unsickled cells in the presence of Lys-Phe was observed after only 15 min incubation. This result, together with measurements of uptake both into the cell and onto the cell membrane shows that the compound produces a membrane-mediated antisickling effect in addition to the effect on haemoglobin in solution within the cell. The membrane effect is not due to a change in cell volume. The properties of this dipeptide may be of value in the treatment of impending and early sickle crisis.

Light scattering measurements supporting helical structures for chromatin in solution.

Laser light scattering measurements have been made on a series of polynucleosomes containing from 50 to 150 nucleosomes. Radii of gyration have been determined as a function of polynucleosome length for different ionic strength solutions. The results suggest that at low ionic strength the chromatin adopts a loosely helical structure rather than a random coil. The helix becomes more regular on increasing the ionic strength, the dimension resembling those proposed by Finch and Klug for their solenoid model.

Subunit associations among chromatin particles.

The self-association of oligonucleosomal chromatin particles in solution has been studied by light scattering and sedimentation. In the absence of magnesium ions no association is observed. In the presence of 70mM sodium or 2mM magnesium ions mono, di, tri and tetranucleosomes self-associate only if they contain bound histone 1. This association leads to the formation of compact aggregates and is continuous and non-cooperative. The relevance to higher order arrangements of nucleosomes is discussed.

Structural studies of encephalomyocarditis virus RNA both in situ and in free solution.

The secondary structure of encephalomyocarditis (EMC) virus RNA has been studied in situ and in free solution by absorbance-temperature relationships and by circular dichroism (CD). Extracted EMC virus RNA melts reversibly and has a hypochromicity of about 20%; analysis of CD spectra and formaldehyde treatment suggests that approx. 60% of the nucleotides are involved in base-pairing at 25 degrees C. It is shown that the RNA within the virus particle is less structured than when it exists in free solution, being partially stabilized by capsid protein against melting until the virion is disrupted to release the intact RNA. Upon clarification to remove denatured capsid protein, the released RNA gives a melting profile identical with that of phenol-extracted virus RNA. The results suggest that the intact structure of the virus is dependent upon intimate non-covalent bonds between RNA and protein together with hydrophobic bonds between the protein subunits.

The structure of the chromatin core particle in solution.

The shape and size of the nucleosomal core particle from chromatin has been examined by analysis of neutron and X-ray scattering data from dilute solutions. Calculations of scattering for many different models have been made and only one model was able to account for both the X-ray and neutron profiles. This model is an oblate structure with height about 50A and diameter 110A. The DNA is mainly confined to two annuli located at the top and bottom respectively of the core particle positioned on the outside of a compact protein core which has a height of about 40A and diameter about 73A.