Mechanical measures during maximal velocity knee extension exercise and their relation to fibre composition of the human vastus lateralis muscle

A method for measuring the maximal velocity of knee extension exercise is described using a very light lever arm. Instrumentation of the lever arm with a potentiometer and accelerometer also allows for the measurement of peak acceleration, time to peak acceleration, the average rate of development of acceleration (jerk) and peak torque. With this apparatus and surface electromyography, electromechanical delay (EMD) was also determined. This apparatus was tested using 17 female and 10 male subjects, and the measures obtained were related to the percentage of fast twitch fibres (% FT) and the relative area of fast twitch fibres (% FTA) in the vastus lateralis determined from duplicate muscle biopsy samples. Peak velocity of unloaded knee extension averaged 12.1 +/- 1.2 and 12.2 +/- 1.7 rad.s-1 for females and males, respectively, and were not significantly different. As well, peak acceleration, time to peak acceleration jerk and EMD values were not significantly different between the female and male subjects, but the mean peak torque for the female subjects (73.5 +/- 14.7 N.m) was significantly lower than that for the males (98.4 +/- 31.5 N.m). Peak acceleration was significantly correlated with %FT (r = 0.40, P = 0.04) for the total subject population. None of the other measures was significantly related to either %FT or %FTA for the male and female subjects or the combined population of subjects.     

Viscosity and transient solvent accessibility of Trp-63 in the native conformation of lysozyme

We have measured the rates of isotope exchange at the nitrogen of the indole ring of Trp-63 of lysozyme and of L-tryptophan as a function of solution viscosity. We have used two cosolvents, glycerol and ethylene glycol, to modify the relative viscosity. We have derived the appropriate kinetic equations for the alternative possibilities that the exchange takes place either in solution or in the intact protein matrix. Because we chose to study the proton-catalyzed exchange reaction, the rate of it is not expected to be diffusion-limited. We confirmed this by measuring the exchange from tryptophan. These results and the known effects of glycerol and ethylene glycol on the solvation of indole allow us to predict that if the exchange reaction takes place in a protein matrix the effects of the two cosolvents when compared under isoviscous conditions should be identical. This is what we find for Trp-63 in lysozyme at 15, 20 and 26 degrees C. The slope of the linear plot of log k vs. log relative viscosity is 0.6. This strongly supports a model for conformational fluctuations where transient solvation takes place without major changes in protein folding. The most interesting feature of our findings is the fact that a slow reaction admittedly not diffusion-limited shows, when taking place in a protein matrix, a linear dependence on solution viscosity. We suggest that what we observe is the effect of damping of movement of the side chain expressed as a change in the friction along the reaction coordinate in the corresponding phase space. The presence of such effects stresses the validity and usefulness of Kramers model of rate processes for reactions taking place in a protein matrix. Such behavior is predicted by several of the recently proposed general mechanisms of enzyme catalysis.     

Developmental appearance of the Ca2+-binding proteins parvalbumin,calbindin D-28K,S-100 proteins and calmodulin during testicular development in the rat

Summary Calcium and intracellular Ca²⁺-binding proteins are possibly involved in hormone production and spermatogenesis in rat testis. Parvalbumin, calbindin D-28K, S-100 proteins and calmodulin were localized in the Leydig cells, which are sites of testosterone synthesis. Only the appearance of parvalbumin-immunoreactivity is closely correlated to testosterone production during development of the testes. Calbindin D-28K-immunoreactivity persisted in foetal-type Leydig cells and in adult-type Leydig cells at all stages of development. S-100-immunoreactivity was low during all foetal stages, absent between birth and puberty, and increased thereafter. Calmodulin staining is most prominent in the cytoplasm of developing spermatocytes and of maturing spermatids. All four proteins co-exist in the seminiferous tubules. The distinct localization and developmental appearance of these proteins suggests different regulatory roles in Leydig cell function and spermatogenesis.     

A regional localisation for an X-linked suppressor gene (XS) for the Lutheran blood group

Summary Suppression of Lutheran blood group expression is usually associated with an autosomal dominant suppressor gene In(Lu) which results in the rare Lu(a-b-) phenotype. X-linked recessive suppression can also occur under the control of the XS locus with normal (XS1) and suppressor (XS2) alleles. The only known kindred with XS2 segregating was examined for polymorphic DNA markers with known regional localisations on the X chromosome. Two point linkage analysis suggested linkage of XS to DXS14 (p58.1) with =0.00, =1.96. DXS14 is situated near the centromere at Xp11. Recombinants with DXS84 (distal to DXS14 on Xp) and recombinants with DXYS1 (pDP34) (on the proximal part of Xq) suggests a localisation for XS near the centromere, between DXS84 and DXYS1 (Xp21.2-Xq21.1). Linkage to a marker on the X chromosome confirms the original assignment of XS to the X chromosome, which was based on pedigree inspection from this family.     

Activation of a low specific activity form of DNA polymerase alpha by inositol-1,4-bisphosphate

A low activity form of DNA polymerase alpha immunoaffinity-purified from adult-derived human fibroblasts was activated by interaction with phosphatidylinositol-4-monophosphate, while a high activity form of the enzyme did not interact with phosphatidylinositol-4-monophosphate or its derivatives. Phosphatidylinositol-4-monophosphate was apparently hydrolyzed in the presence of a highly purified low activity form of DNA polymerase alpha, effecting the release of diacylglycerol and the retention of inositol-1,4-bisphosphate by the enzyme complex. The resulting inositol-1,4-bisphosphate/protein complex exhibited increased affinity of binding to DNA template/primer and increased deoxynucleotidyltransferase activity. These data indicate that inositol-1,4-bisphosphate may function as an effector molecule in the activation of a low activity form of human DNA polymerase alpha and suggest that it may function as a second messenger during the initiation of mitosis in stimulated cells.     

Autoradiographic localization of leukotriene C4 and D4 binding sites in guinea-pig lung

Binding of [3H] leukotriene C4 and D4 to guinea-pig lung sections was charaterised and binding sites were localized by autoradiography. Both leukotrienes bound to guinea-pig lung sections and membranes with high affinity and with similar charateristics to binding in a membrane preparation. Autoradiography revealed that the distribution of LTC4 and D4 binding sites was markedly different. Smooth muscle and epithelium of central and peripheral airways were densely labelled with [3H]LTC4; vascular smooth muscle and alveolar walls were also labelled. With [3H]LTD4, however, there was no detectable labelling of airways or vessels but subtantial labelling of alveolar walls. This lends futher support that LTC4 and LTD4 binding sites differ and may not be identical with functional receptors.     

去甲肾上腺素在大鼠缰核引起的心血管效应及其机制

在乌拉坦麻醉的大鼠,研究了去甲肾上腺素(NE)在缰核(Hb)引起的心血管效应及其机制。Hb内微量注射NE使平均动脉压和心率呈剂量依赖性增加。用α受体阻断剂酚妥拉明预处理Hb,可明显减弱NE在Hb引起的心血管效应,但β受体阻断剂心得安或生理盐水不引起任何影响。Hb内微量注射海人酸使平均动脉压和心率明显增加,但Hb内微量注射利多卡因则不能引起明显的心血管效应。上述结果表明,Hb内NE在调节心血管活动中起重要作用,而这种效应可能是通过激活α受体使Hb兴奋的结果。     

Mutations in yeast U5 snRNA alter the specificity of 5' splice-site cleavage

Recognition of 5' splice sites in pre-mRNA splicing is achieved in part by base pairing with U1 snRNA. We have used interactive suppression in the yeast Saccharomyces cerevisiae to look for other factors involved in 5' splice-site recognition. This approach identified an extragenic suppressor that activates a cryptic 5' splice site. The suppressor is a gene for U5 snRNA (snR7) with a single base mutation in a strictly conserved 9 base sequence. This suggests that U5 snRNA can play a part in determining the position of 5' splice-site cleavage. Consistent with this, we have been able to isolate other mutations in the 9 base element in U5 snRNA that specifically activate a second cryptic 5' splice site nearby.