Fluorescence study of the conformational properties of myoglobin structure. 3. pH-dependent changes in porphyrin and tryptophan fluorescence of the complex of sperm whale apomyoglobin with protoporphyrin IX; the role of the porphyrin macrocycle and iron in formation of native myoglobin structure.

The porphyrin and tryptophan fluorescence of sperm whale apomyoglobin complexed with protoporphyrin IX has been studied in the pH range 2-13. It has been shown that the fluorescence and absorption spectra of protoporphyrin incorporated into the heme crevice remain constant in the pH range 5.5-10.

Fluorescence study of the conformational properties of myoglobin structure. 2. pH- and ligand-induced conformational changes in ferric- and ferrousmyoglobins.

Tryptophanyl fluorescence of high-spin and low-spin complexes of sperm whale ferric- and ferrousmyoglobins, met-, azide- and cyanomyoglobins and deoxy-, oxy- and carboxymyoglobins has been studied in the pH range 2.5-13. The pH-dependent fluorescence of sperm whale metmyoglobin acylated at the N-terminal alpha-amino group by methylisothiocyanate and of bovine metmyoglobin, which contains invariant Trp7 and Trp14 but lacks Tyr151, have also been examined.

Fluorescence study of the conformational properties of myoglobin structure. 1. pH-dependent changes of tryptophanyl fluorescence in intact and chemically modified sperm whale apomyoglobins.

The pH-dependent fluorescence of intact sperm whale apomyoglobin (apo-Mb) containing two tryptophans at positions 7 and 14, and of apo-Mb derivatives modified on Trp7 by 2-hydroxy-5-nitrobenzyl bromide (Koshland reagent) and o-nitrophenylsulphenyl chloride, has been studied. The fluorescence of apomyoglobins modified at His residues by iodoacetamide and bromoacetate, and at the N-terminal alpha-NH2 group by methylisothiocyanate, has also been investigated. The individual fluorescent properties of both tryptophans and their contributions to the total spectrum of apo-Mb have been resolved within the pH range 2-12.

Parametric resonance and amplification in excitable membranes. The Hodgkin-Huxley model.

It has previously been shown by different investigators that the excitable membrane shows a resonant sensitivity to periodic external perturbations, but its Q-factor is, as a rule, low. The present paper analyses the possible ways of increasing the membrane Q, using a model of the Hodgkin-Huxley type. It is found, in particular, that it can be increased considerably by modulating periodically the membrane capacitance or the activation and inactivation rate constants of ionic channels, with a frequency of about 2 fo (fo being the fundamental frequency of damped oscillations in the membrane), the extent of modulation not exceeding the critical value 2/Q.