1. l-Asparaginases from Erwinia carotovora and Escherichia coli (EC2 enzyme) are both capable of inhibiting and eliminating certain types of tumour cells. The Er. carotovora enzyme is a more basic protein, however, and in contrast with the EC2 enzyme it contains neither tryptophan nor cystine, and disulphide bonds are therefore absent. The molecule is very stable in solution from pH3.0 to about pH12.0, and is somewhat more stable at alkaline pH than is the Esch. coli enzyme. Calculations based on a s(0) (20,w) 7.43S and a sedimentation-equilibrium molecular weight of 135000+/-10000 give a frictional ratio (f/f(0)) of 1.08. The molecular conformation is therefore very compact in solution, and the electron microscope shows the negatively stained molecules as almost spherical particles with a diameter of 7.2+/-0.7nm. 2. Sedimentation-velocity and equilibrium ultracentrifugation, in 5-8m solutions of urea and guanidinium chloride, and also electrophoresis in sodium dodecyl sulphate-polyacrylamide gel, reveal a dissociation of the native protein molecule into four subunits of similar molecular weight in the range 32500-38000. The enzymically inactive subunits can be physically reassembled into an active tetramer when urea is removed by dialysis. Although the subunit structures of the Er. carotovora enzyme and the Esch. coli enzyme molecules are similar, the secondary bonding forces holding the subunits together in the tetramer are somewhat stronger in the Er. carotovora enzyme. 3. The optical-rotatory-dispersion (o.r.d.) parameters that characterize the Cotton effects arising from ordered structure in the molecule are [m'](233)=-3522+/-74 degrees and [m'](200)=9096+/-1700 degrees . These show very marked changes as the secondary structure is disrupted and the molecule dissociates into subunits. A correlation pathway was traced on the basis of o.r.d. parameters and enzyme activity as the polypeptide chains were denatured and renatured (and reconstituted) into active molecules after the dilution of solutions in urea. Subunits resulting from treatment with sodium dodecyl sulphate do not show the typically disordered o.r.d. profile, but nevertheless they are inactive.

Records of burbot Lota Iota (L.) captures from the early nineteenth century to the present have been gathered and arranged watershed by watershed in chronological order. Most are from eastward-flowing river systems from Durham southwards to the Grcat Ouse, but a few records from westward-flowing systems are considered. In many areas the records imply a decline of burbot numbers and distribution during the present century, though burbot may never have been more than locally abundant. Local over-fishing, pollution and habitat changes are considered the most likely causes of decline. Conservation measures seem desirable.

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The cyclic polypeptide alamethicin, when incorporated into a lipid bilayer imparts ion-gating properties resembling the electrical characteristics of natural membranes more closely than any other synthetic system. A model is described in which the molecule assumes a disc-like conformation, with the cyclic polypeptide structure extending around the circumference [l] . Physical studies [2,3] indicate a high lipid solubility, and specific interaction with phospholipids in artificial systems. Following the determination of the amino acid sequence of alamethicin, the model has been modified to accommodate this and also the previously undetected cyclising y-linked side chain, -Glu-Gln. The presumed ion binding groups have been located at the centre, in the form of a molecular pore [4]. We have examined the conformational properties of alamethicin in a variety of solvents by ORD and CD. The spectroscopic results indicate that the molecule assumes a compact conformation in hydrophobic environments. We propose that this conformation, which may contain up to 40% helical structure, is significant in the action of alamethicin on bilayer membranes.The ORD and CD spectra are strongly solvent sensitive, showing greater amplitude with increasing hydrophobicity of the solvent. Fig. 1 shows the increase (more than 2-fold) in the negative troughs in CD at 207 nm and 220 nm on going from 10% ethanol in water to 100% ethanol. Similar effects have been found for methanol, dioxane and acetonitrile. Intensification of this spectrum is found in the presence of 278 detergents such as 1% sodium dodecyl sulphate ( fig. l), 1% sarkosyl and 5% sodium deoxycholate, though in these cases the 207 nm trough is less pronounced.