Biochemistry of protein-isocyanate interactions: a comparison of the effects of aryl vs. alkyl isocyanates.

In addition to their use in the polyurethane and pesticide industries, isocyanates have proven to be useful probes for the exploration of protein structure. This paper focuses on three aspects of isocyanates: their broad reactivity, their reversible interaction with cholinesterases, and the relative hydrolysis rates of alkyl and aryl isocyanates. The broad reactivity of isocyanates as well as the demonstrated affinity labeling of serine and sulfhydryl esterases are discussed.

A high-resolution 1H-NMR investigation of the histidine-binding protein J of Salmonella typhimurium. Substrate-induced conformational changes.

High-resolution 1H-NMR spectroscopy at 600 MHz has been used to investigate the conformational transitions of the histidine-binding protein J of Salmonella typhimurium in solution as a function of pH and of L-histidine concentration. The dissociation constant for the binding of L-histidine to histidine-binding protein J increases from 6.0 X 10(-8) to 5.

Proton nuclear magnetic resonance studies of isonitrile-heme protein complexes.

Steric interactions between bound ligand molecules and the valine E11 methyl groups of human hemoglobin and sperm whale myoglobin have been examined directly by high resolution NMR techniques. The methyl proton resonances of this amino acid are shifted markedly upfield and away from the bulk of the protein resonances by the shielding effect of circulating pi electrons in the porphyrin ring. We have monitored the valine resonance in the presence of CO and a series of isonitriles and found considerable shifts in its position, both between the various protein complexes and among the different liganded states.

Phytochrome induces photoreversible calcium fluxes in a purified mitochondrial fraction from oats.

Previous studies have indicated that phytochrome regulates Ca(2+) fluxes across the plasma membrane of plant cells. In this study we investigated whether phytochrome can also regulate such fluxes across mitochondrial membranes, using the Ca(2+)-sensitive dye murexide to monitor the uptake and release of Ca(2+) by mitochondria. The results showed that Ca(2+) fluxes in these organelles could be photoreversibly altered, red light diminishing the net uptake rate and far-red light restoring this rate to its dark control level.

Modulation of a mitochondrial function by oat phytochrome in vitro.

Previous data in the literature have indicated that phytochrome could alter the rate of reduction of exogenously added NADP by a pea mitochondrial preparation in vitro. These results could not be duplicated using a mitochondrial preparation isolated from etiolated oat seedlings. Further experimentation demonstrated that the addition of Pr to the preparation, in combination with a far red light illumination, could significantly reduce the rate of oxidation of NADH by the external dehydrogenases of oat mitochondria.