Diffusion-limited kinetics of the solution-solid phase transition of molecular substances

For critical tests of whether diffusion-limited kinetics is an option for the solution-solid phase transition of molecular substances or whether they are determined exclusively by a transition state, we performed crystallization experiments with ferritin and apoferritin, a unique pair of proteins with identical shells but different molecular masses. We find that the kinetic coefficient for crystallization is identical (accuracy 相似文献   

Some features of different motor units in human biceps brachii

Summary Use has been made of the method of selective leading-off of impulses from individual motor units at high isometric muscle tension, the maximum one including. Two types of motor units have been distinguished in m. biceps brachii in man on the basis of the dependence between the firing frequency and the level of the muscle tension. Characteristic of the first (tonic) type is the rise in the frequency at lower tensions and constant frequency at higher tensions. The second (phasic) type shows an approximately linear rise of the frequency with increase of tension. The tonic motor units are smaller in size, with lower threshold, they are less fatiquable and their transient pattern of firing depends on the rate of increase of tension. They contribute less to the growth of the muscle tension. The phasic motor units are bigger in size with higher threshold, more fatiguable, their transient pattern of firing does not depend on the rate of increase of tension. They contribute essentially to the growth of the muscle tension.     

Retrovirus budding

The release of retrovirus particles from the infected cell is greatly stimulated by short motifs, known as "late" or "L" domains, present within the Gag precursor protein. Three distinct classes of L domains have been identified; these bear the core sequence: Pro-Thr/Ser-Ala-Pro [P(T/S)AP], Pro-Pro-x-Tyr (PPxY), or Tyr-Pro-x-Leu (YPxL). A number of recent studies have demonstrated that L domains function by interacting with components of the machinery responsible for sorting cellular proteins into the multivesicular body (MVB) pathway. This review traces the history of L domain discovery and characterization, and highlights the relationship between L domain activity, retrovirus release, and the host endosomal sorting machinery.     

Morphometric analysis of the fiber populations of the rat sciatic nerve, its spinal roots, and its major branches

Correspondence between the nerve composition and the functional characteristics of its fiber populations is not always evident. To investigate such correspondence and to give a systematic picture of the morphology of the rat hind limb nerves, extensive morphometric study was performed on the sciatic nerve, its founding dorsal and ventral spinal roots, and its major branches. Nerve histology was examined in semithin sections via microscopic image analysis. Variation in the density of myelinated fibers, fiber interspace, and nerve cross-sectional area was studied in individual roots and nerves. In the dorsal roots, fiber numbers and cross-sectional areas were directly linearly proportional to the spinal root level number. Constituent fiber populations were identified using multicomponent lognormal models, and an optimal model for every nerve or root was selected by using an information theoretic approach. For the dorsal and ventral roots and the sciatic and peroneal nerves, optimal fiber population models consisted of three components, whereas, for the tibial and sural nerves, two components were optimal. Functional identities of the revealed fiber populations were established by using calculations of corresponding conduction velocities according to Arbuthnott et al. (J. Physiol. [1980] 308:125-157) and anatomical considerations. It is anticipated that morphological parameters established in this study would advance the development of neural prostheses in humans. The proximodistal correspondences among the fiber populations of different nerves were established by parametric statistical comparisons. The proposed approach provides a conceptual framework for understanding the comparative anatomy of the peripheral nerves and spinal roots and can be further applied in other species.     

Interactions among peroxisome proliferator activated receptor-gamma, insulin signaling pathways, and steroidogenic acute regulatory protein in human ovarian cells

CONTEXT AND OBJECTIVE: Peroxisome proliferator activated receptor-gamma (PPAR-gamma) agonists thiazolidinediones (TZDs) are thought to ameliorate hyperandrogenism in polycystic ovary syndrome by reducing hyperinsulinemia. However, TZDs also exhibit direct effects in the human ovary. We examined interactions among PPAR-gamma, insulin signaling pathways, and steroidogenic acute regulatory (StAR) protein in human ovarian cells. MATERIALS AND METHODS: Mixed human ovarian tissue culture that contained granulosa, theca, and stromal cells, and a culture of purified granulosa cells obtained during in vitro fertilization, were established as previously described. Cells were cultured in the presence or absence of insulin, with or without 25 or 50 microm rosiglitazone or pioglitazone. Expression of PPAR-gamma, insulin receptor, or insulin receptor substrate (IRS)-1 in both cell systems and of the StAR protein in granulosa cells was measured using immunoprecipitation and immunoblotting. RESULTS: Rosiglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 168% (P < 0.05), 679% (P < 0.006), 290% (P < 0.037), and 323% (P < 0.01) of baseline, respectively. Pioglitazone stimulated expression of PPAR-gamma, insulin receptor alpha- and beta-subunits, and IRS-1 up to 222% (P < 0.01), 362% (P < 0.001), 402% (P < 0.029), and 492% (P < 0.03), respectively. Insulin alone stimulated expression of PPAR-gamma, alpha-subunit and beta-subunit of insulin receptor, and IRS-1 up to 174% (P < 0.001), 692% (P < 0.014), 275% (P < 0.024), and 431% (P < 0.01), respectively. In purified granulosa cell culture, rosiglitazone stimulated expression of StAR protein up to 540% (P < 0.007), and pioglitazone stimulated expression of StAR protein up to 670% (P < 0.007). Insulin alone stimulated expression of StAR protein up to 600% (P < 0.012). CONCLUSIONS: Insulin and TZDs independently stimulate expression of PPAR-gamma, insulin receptor, IRS-1, and StAR protein in human ovarian cells. Thus, PPAR-gamma, insulin receptor with its signaling pathways, and StAR protein constitute a novel human ovarian regulatory system with complex interactions among its components.     

Low-dose thalidomide in combination with oral fludarabine and cyclophosphamide is ineffective in heavily pre-treated patients with chronic lymphocytic leukemia

Elevated levels of TNF-alpha have been associated with progressive disease in patients with chronic lymphocytic leukemia (CLL). Thalidomide has been shown to inhibit production of TNF-alpha. We investigated the effects of thalidomide on clinical outcome and TNF-alpha serum levels in five pre-treated CLL patients. The schedule consisted on daily thalidomide (Thal), oral fludarabine (Flu) and oral cyclophosphamide (CTX). Median duration of treatment was 60 days; four patients stopped treatment for disease progression and one patient for neurological toxicity. Serum TNF-alpha levels did not show any decrease during treatment. Low-dose thalidomide is not effective in CLL patients with refractory disease.