The binding of calcium ions to hemocyanin from Levantina hierosolima at physiological pH

Regeneration of Aplysia bag cell neurons is synergistically enhanced by substrate-bound hemolymph proteins and laminin

We have investigated Aplysia hemolymph as a source of endogenous factors to promote regeneration of bag cell neurons. We describe a novel synergistic effect between substrate-bound hemolymph proteins and laminin. This combination increased outgrowth and branching relative to either laminin or hemolymph alone. Notably, the addition of hemolymph to laminin substrates accelerated growth cone migration rate over ten-fold. Our results indicate that the active factor is either a high molecular weight protein or protein complex and is not the respiratory protein hemocyanin. Substrate-bound factor(s) from central nervous system-conditioned media also had a synergistic effect with laminin, suggesting a possible cooperation between humoral proteins and nervous system extracellular matrix. Further molecular characterization of active factors and their cellular targets is warranted on account of the magnitude of the effects reported here and their potential relevance for nervous system repair.

The role of copper and quaternary structure on the conformational properties of Octopus vulgaris hemocyanin

Some structural properties of Octopus vulgaris hemocyanin have been investigated by fluorescence spectroscopy. The three-dimensional structure of Octopus hemocyanin is remarkably tight, resulting in a deep burial of almost all the tryptophyl residues of the protein. The hemocyanin conformation has been studied in the two main aggregation states (11 S, 50 S) of the protein, and with respect to the presence or absence of copper in the active site. Upon changing the pH of the solution, Octopus hemocyanin in the 50 S aggregation state can assume at least three different conformations. During the transition between each conformation the fluorescence quantum yield changes, but the environment of tryptophans does not change. Dissociation of the protein from 50 S to 11 S strongly enhances its susceptibility toward denaturating agents such as pH or temperature, and modifies the effects of fluorescence quenchers such as acrylamide. Moreover, these effects are more pronounced when copper is removed from the active site. A comparative analysis of the results shows that the subunit-subunit interactions exerted within the 50 S species are more important in the maintenance of the conformational stability than the copper ions present in the active sites. This behavior can be accounted for by the large amount of Ca(II) ions linked to 50 S hemocyanin.

The dependence of the conductance of the hemocyanin channel on applied potential and ionic concentration with mono- and divalent cations

Incorporation of Megatura crenulata hemocyanin into phosphatidylcholine black lipid membranes results in the formation of ion channels. Channel properties depend on many factors, three of which are examined in this work: type and concentration of electrolyte and applied voltage. Eight cations at different concentrations have been used. Instantaneous conductance of the channel is a saturating function of both applied voltage and ionic strength of the bathing solution with monovalent cations, but only of ionic strength with divalent cations. Steady-state voltage-conductance relations are nonlinear for both signs but show slight saturation with ionic strength. Relaxation towards the steady state can be fitted by two exponentials with different time constants. All experimental data are fitted postulating the existence of a mechanism of voltage gating of the channel, and of discrete negative charge near its mouth. Specific and nonspecific binding of cations is required.

Haemocyanins

About ten years ago, one of the authors participated in a review of haemocyanin structure and function (van Holde & van Bruggen, 1971). At that time, it was possible to describe the field in terms of a limited amount of exciting new structural information, and a long list of unanswered questions. While the stoichiometry of oxygen binding was understood, virtually nothing was known about the active site. Even the oxidation state of the copper was a matter of conjecture. The size of the haemocyanin polypeptide chains was the subject of intense debate, with very little substantive knowledge available. While the haemocyanins were known to be allosteric proteins, there were virtually no experimental studies of oxygen binding on a level that could be meaningfully interpreted in terms of extant theories.

A light-scattering study of the effect of calcium chloride on the molecular weight of Busycon hemocyanin

Solutions of Busycon canaliculatum have been studied by light scattering. In 0.05 M Trizma buffer +0.1 M NaCl at pH 7.0 at 14 degrees, the weight-average molecular weight is 8.9 X 10(6). In the presence of added CaCl2 (0.02 M), the molecular weight of the protein increases to 10.7 X 10(6), and the second virial coefficient is reduced. At pH 9.95, the molecular weights with and without 0.02 M CaCl2, are 3.7 X 10(6) and 1.3 X 10(6), respectively; and the effect of Ca++ in reducing the second virial coefficient is much greater than at pH 7.0. These results can be understood on the basis that at pH 7.0, ca++ increases the association of hemocyanin, by binding and intermolecular linkage through the carboxyl groups of protein side chains. At pH 9.95, amino groups are deprotonated and therefore also become available for Ca++ binding. The relative effect of Ca++ in enhancing the association of hemocyanin therefore becomes greater at the higher pH.