Preparation and isolation of a taste bud-derived fraction from bovine circumvallate papillae.

A crude extract from taste buds was prepared from circumvallate papillae of bovine tongues by a procedure consisting of freezing, coring, excision, treatment with hypotonic buffer, nitrogen pressurization and selective homogenization. Examination of taste buds by light and electron microscopy before and after this procedure indicated that some of the contents of the buds, mainly from the more apical portions, was extruded following the procedure; anatomical changes could not be observed in the epithelial tissue immediately surrounding the taste buds.     

Zinc in taste function

Zinc has been associated with taste function in humans at several levels of organization—the taste bud, the nerves transmitting taste information, and the brain. Zinc plays specific yet varied roles at each organizational level, although many of these roles have not been clearly identified. They include participation in the structural architecture of the cell, maintenance of cell membrane integrity, and control of activity of several cytoplasmic and membrane enzymes. Early investigators noted that some patients given drugs that altered zinc metabolism or who experienced disease processes associated with abnormalities of zinc metabolism exhibited taste dysfunction. Because of these findings zinc was given to a variety of patients as treatment for taste dysfunction. Initial treatment success was observed, but was quickly tempered by more extensive studies that yielded widely variable results leading to confusion about the role of zinc in both taste function and taste treatment. Further studies revealed that taste disorders were diverse and complex with multiple underlying pathophysiologies that were little understood. Subsequent work by several investigators revealed that patients with zinc deficiency, of any etiology, exhibited taste dysfunction and that treatment of these patients with zinc usually produced improvement of clinical symptoms. These results raised the question of how to define zinc deficiency, for zinc treatment in patients without zinc deficiency was unsuccessful and these patients represent more than three-quarters of all patients with taste dysfunction. New clinical techniques for the definition of human zinc deficiency have been achieved through the use of binding and displacement of⁶⁵Zn on specific sites on erythrocyte membranes; these results offer a guide to the identification of patients (i.e., those with zinc deficiency) who may benefit from zinc treatment.     

The S(MK) box is a new SAM-binding RNA for translational regulation of SAM synthetase

We have identified the S(MK) box as a conserved RNA motif in the 5' untranslated leader region of metK (SAM synthetase) genes in lactic acid bacteria, including Enterococcus, Streptococcus and Lactococcus species. This RNA element bound SAM in vitro, and binding of SAM caused an RNA structural rearrangement that resulted in sequestration of the Shine-Dalgarno (SD) sequence. Mutations that disrupted pairing between the SD region and a sequence complementary to the SD blocked SAM binding, whereas compensatory mutations that restored pairing restored SAM binding. The Enterococcus faecalis S(MK) box conferred translational repression of a lacZ reporter when cells were grown under conditions where SAM pools are elevated, and mutations that blocked SAM binding resulted in loss of repression, demonstrating that the S(MK) box is functional in vivo. The S(MK) box therefore represents a new SAM-binding riboswitch distinct from the previously identified S box RNAs.     

Mutations that affect flightin expression in Drosophila alter the viscoelastic properties of flight muscle fibers

Striated muscles across phyla share a highly conserved sarcomere design yet exhibit broad diversity in contractile velocity, force, power output, and efficiency. Insect asynchronous flight muscles are characterized by high-frequency contraction, endurance, and high-power output. These muscles have evolved an enhanced delayed force response to stretch that is largely responsible for their enhanced oscillatory work and power production. In this study we investigated the contribution of flightin to oscillatory work using sinusoidal analysis of fibers from three flightless mutants affecting flightin expression: 1) fln⁰, a flightin null mutant, 2) Mhc¹³, a myosin rod point mutant with reduced levels of flightin, and 3) Mhc⁶, a second myosin rod point mutant with reduced levels of phosphorylated flightin. Fibers from the three mutants show deficits in their passive and dynamic viscoelastic properties that are commensurate with their effect on flightin expression and result in a significant loss of oscillatory work and power. Passive tension and passive stiffness were significantly reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. The dynamic viscous modulus was significantly reduced in the three mutants, whereas the dynamic elastic modulus was reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. Tension generation under isometric conditions was not impaired in fln⁰. However, when subjected to sinusoidal length perturbations, work-absorbing processes dominated over work-producing processes, resulting in no net positive work output. We propose that flightin is a major contributor to myofilament stiffness and a key determinant of the enhanced delayed force response to stretch in Drosophila flight muscles. flight muscles; muscle mutants; myosin