Conformationally altered aortic myosin light chains

Aorta smooth myosin contains two types of light chain, LC20 and LC17, which fold together with the N-terminal region of each heavy chain to form the globular head region of myosin. We demonstrate an altered conformation of LC20 after its separation from heavy chain by high concentrations of urea, on the basis of the following evidende: 1) A polyclonal antibody against LC20 was not able to recognize this conformationally altered form; 2) Myosin reconstituted from heavy chains and urea-dissociated light chains exhibited extremely low ATPase activity. Circular dichroism unfolding profiles showed that light chains dissociated from heavy chains by SDS appeared to be more stable than those generated by urea dissociation.     

Characterization of cDNA of lycopene beta-cyclase responsible for a high level of beta-carotene accumulation in Dunaliella salina.

Lycopene beta-cyclase (Lyc-B) is the key enzyme in the catalysis of linear lycopene to form cyclic beta-carotene, an indispensable part of the photosynthetic apparatus and an important source of vitamin A in human and animal nutrition. Studies showing that the microalga Dunaliella salina can accumulate a high level of beta-carotene are lacking. We hypothesize that D. salina is closely involved with the catalytic mechanism of Lyc-B and the molecular regulation of its gene. In this study, we used RT-PCR and RACE-PCR to isolate a 2475 bp cDNA with a 1824 bp open reading frame, encoding a putative Lyc-B, from D. salina. Homology studies showed that the deduced amino acid sequence had a significant overall similarity with sequences of other green algae and higher plants, and that it shared the highest sequence identity, up to 64%, with Lyc-B of Chlamydomonas reinhardtii. Codon analysis showed that synonymous codon usage in the enzyme has a strong bias towards codons ending with adenosine. Two motifs were found in the Lyc-B sequence, one at the N terminus, for binding the hypothetical cofactor FAD, and the other was a substrate carrier motif in oxygenic organisms shared by an earlier carotenogenesis enzyme, phytoene desaturase, and Lyc-B. A tertiary structure prediction suggested that the catalytic or binding site structure within LycB from D. salina is superior to that of both H. pluvialis and C. reinhardtii. The LycB protein from D. salina was quite removed from that of H. pluvialis and C. reinhardtii in the phylogenetic tree. Taken as a whole, this information provides insight into the regulatatory mechanism of Lyc-B at the molecular level and the high level of beta-carotene accumulation in the microalga D. salina.     

Quantitative EMG analysis to investigate synergistic coactivation of ankle and knee muscles during isokinetic ankle movement. Part 2: time frequency analysis.

Fundamental to intralimb coordination in the lower extremity, ankle-knee synergy induced by motor irradiation has long been employed to secure facilitation of paralyzed muscles. This study, a companion research subsequent to the time amplitude analysis of surface electromyography in part 1, was to investigate the recruitment strategy of irradiated muscles and prime movers during ankle isokinetic contraction at different contraction speeds (30, 60, 120 and 240 degrees/s) with time frequency analysis. The results indicated the recruitment strategies of the major irradiated muscles (ipsilateral rectus femoris/ipsilateral biceps femoris) and prime movers (anterior tibialis/gastrocnemius) were time-dependent and significantly different in terms of the instantaneous median frequency. In general, the prime movers for ankle isokinetic concentric contraction demonstrated a similar recruitment strategy, irrespective of different contraction speeds. This finding is consistent with the idea of generalized motor programs that speed is one of the constraint parameters supplied to motor programs. Nevertheless, the recruitment strategies of the irradiated muscles were highly inconsistent, varying across trials at different contraction speeds, and were not relevant to those of the prime movers. In addition, the recruitment in the irradiated muscles seemly limited to motor units of low threshold, in spite of maximal voluntary contraction of the prime movers.