Occurrence and seasonal variation of 19-norcholest-4-en-3-one and 3 beta-monohydroxy sterols in the Californian gorgonian, Muricea californica

The first natural occurrence of 19-norcholestenone is reported, together with 17 sterols and one other delta 4-3-ketone in the extracts of the Californian gorgonian, Muricea californica (Aurivillius). Six additional demethyl sterols and five additional 4-monomethyl sterols which remain unidentified were also detected. Lipid extracts of M. californica from a winter and summer collection were split by various chromatographic methods into free sterol, steryl ester, and steryl conjugate fractions. Sterol compositions (determined by CG and CG-MS) of each fraction, subsequent to hydrolysis, are tabulated and discussed with respect to plausible origins of observed variations. The possible relationship of the Muricea 19-nor-steroidal ketone to other naturally occurring 19-nor-steroids is discussed.     

A double helix B-type geometry based on high-resolution proton NMR of single-helical DNA fragments: d(TA)5 x d(TA)5.

A single-helical B-type geometry is presented based on 1H NMR observations on d(TATA) and several other small single-helical DNA fragments. The structure is extended to one complete turn of double-helical DNA and its characteristics are compared with other known B-type structures.     

Transient Phases of the Isometric Tetanus in Frog's Striated Muscle

In an isometric tetanus in frog's sartorius muscle tension approaches the plateau exponentially with rate constant α. α a depends on sarcomere length, s, and temperature, T, according to the Arrhenius equation See PDF for Equation for temperatures between 1 and 20°C and for sarcomere lengths 2.0–2.8 µm. The energy of activation, E, does not vary significantly with s; E = 13.9 ± 2.4 kcal/mole. A(s) decreases monotonically with s; A(2.1 µm) is about three times greater than A(2.8 µm). Late in relaxation active tension approaches zero exponentially with rate constant r. r decreases exponentially with increasing duration of tetanus, D, from r₀ in a twitch to r_∞ for large D. The rate constant for decrease of r with D increases with s and with T. r₀ and r_∞ obey the Arrhenius equation and decrease with increasing s.     

Nerve interactions and regenerative processes occurring in newt limbs fused end-to-end

Peripheral nerve interactions and regenerative phenomena were studied in newt forelimbs fused end to end. After simple fusion, one or two spikelike structures regenerated at the plane of fusion in 88% of the cases. When one of the limbs was denervated at the time of fusion, no regeneration occurred from the plane of fusion. If the limbs were fused and one was amputated at the shoulder more than 10 days after fusion, regeneration from the amputation surface did not occur. When the limbs were reamputated 30 days later, regeneration of left limbs from the proximodistally reversed right limb stumps followed. If one of the limbs was denervated at the time of fusion, and amputation was subsequently carried out through the formerly denervated limb, regeneration always took place after the first amputation. On the basis of these results it is postulated that when regenerating nerves of opposite proximodistal polarity meet head-on, the majority of fibers, at least, do not grow into territories occupied by the other nerve. These results have also demonstrated that full limb regeneration can occur at a greater distance from the midline than the end of a normal limb. These experiments also provide a technique for artificially elongating peripheral nerves.