Role of plasma and serum proteases in the degradation of elastin

Accelerated proteolysis of tropoelastin and elastin occurs in the major arteries of chicks fed copper-deficient diets. Signs of elastin degradation are not obvious in normal arteries of copper-supplemented chicks. It is proposed that the sources of proteases that effect elastin degradation are from plasma and serum. Both calcium-dependent proteases and kallikrein were effective in degrading tropoelastin and partially crosslinked insoluble elastin into peptides similar to those detected in aortic extracts from copper-deficient chicks. As dietary copper deficiency progresses it is also possible to detect elastin peptides in plasma.     

Temperature-dependent paramagnetism in melanin polymers

Electron spin resonance measurements on hydrated suspensions of melanin polymers at neutral pH have revealed that their spin concentrations are temperature dependent. It is shown that changes in spin concentration with temperature are rapid and completely reversible. This novel behavior is not found in frozen or dried melanin preparations. The implications of these findings with respect to melanin organization and monomer-monomer interactions are discussed. It is argued that the spin concentration in melanin suspensions is largely governed by an intragranular equilibrium involving quinone, hydroquinone, and semiquinone units on the polymer.     

The epidermal glands of Nereis

Summary Three types of unicellular glands have been identified from the parapodial epithelium of Nereis. They conform to a common plan. The cell body, which lies at the base of the epithelium, has prominent rough-faced endoplasmic reticulum and golgi. It sends a long intra-cellular duct to the cuticle where it opens through a pore lined by the epicuticle. The end of the duct in two of the glands bears a ring of microvilli. The duct of the type-6 gland is lined by cytoplasm containing elongated mitochondria and endoplasmic reticulum arranged in an alternating fashion. Each of these organelles is surrounded by an array of longitudionally orientated microtubules. The secretions are contained in membrane bound vesicles. In the type-4 cells the contents are homogeneous, whilst the other two contain distinctive electron-dense granules. The type-4 secretions are PAS negative and alcianophilic, the type-5 secretions are PAS positive and non-alcianophilic whilst the type-6 secretions have a strong affinity for Orange G.This work was supported by a grant from the Science Research Council.     

Evaluation of Coupled Perturbed and Density Functional Methods of Computing the Parity-Violating Energy Difference between Enantiomers

We present new coupled-perturbed Hartree-Fock (CPHF) and density functional theory (DFT) computations of the parity-violating energy difference (PVED) between enantiomers for H₂O₂ and H₂S₂. Our DFT PVED computations are the first for H₂S₂ and the first with the new HCTH and OLYP functionals. Like other “second generation” PVED computations, our results are an order of magnitude larger than the original “first generation” uncoupled-perturbed Hartree-Fock computations of Mason and Tranter. We offer an explanation for the dramatically larger size in terms of cancellation of contributions of opposing signs, which also explains the basis set sensitivity of the PVED, and its conformational hypersensitivity (addressed in the following paper). This paper also serves as a review of the different types of “second generation” PVED computations: we set our work in context, comparing our results with those of four other groups, and noting the good agreement between results obtained by very different methods. DFT PVEDs tend to be somewhat inflated compared to the CPHF values, but this is not a problem when only sign and order of magnitude are required. Our results with the new OLYP functional are less inflated than those with other functionals, and OLYP is also more efficient computationally. We therefore conclude that DFT computation offers a promising approach for low-cost extension to larger biosystems, especially polymers. The following two papers extend to terrestrial and extra-terrestrial amino acids respectively, and later work will extend to polymers.     

The diffusion-concentration product of oxygen in lipid bilayers using the spin-label T1 method

A method is described to measure the oxygen diffusion-concentration product, DO[O2], at any locus that can be probed or labeled using nitroxide radicals. The method is based on the dependence of the spin-lattice relaxation time T1 of the spin label on the bimolecular collision rate with oxygen. Strong Heisenberg exchange between spin label and oxygen contributes directly to T1 of the spin label, while dipolar interactions are negligible. Both time-domain and continuous wave saturation methods for studying T1 are considered. The method has been applied to phospholipid liposomes using fatty acid spin labels. A discontinuity in DO[O2] at the main phase transition was observed.