RESUMO
Electron-microscopic studies revealed that two types of subunits of Panulirus interruptus haemocyanin crystallize in different ways. Homohexamers of subunit a give close-packed two-dimensional crystals whereas homohexamers of subunit c form open two-dimensional arrays. We applied computer-image analysis to these arrays and studied the differences in crystallization properties by combining the electron-microscopic data with amino acid sequence information and the X-ray diffraction model of subunit a.
Assuntos
Hemocianinas/ultraestrutura , Sequência de Aminoácidos , Animais , Cristalização , Hemocianinas/isolamento & purificação , Substâncias Macromoleculares , Microscopia Eletrônica , Modelos Moleculares , Dados de Sequência Molecular , Nephropidae , Conformação Proteica , Difração de Raios XRESUMO
Upon trypsinolysis Helix pomatia beta-hemocyanin forms long tubular structures, which appear to be linear polymers of hemocyanin molecules from which the collar structure has been removed. Polyacrylamide gel electrophoresis in the presence of sodium dodecylsulfate shows that only few peptide bonds are hydrolyzed by trypsin. The structure of the polymers has been investigated by electron microscopy, combined with optical diffraction. Preliminary X-ray diffraction data are presented. Functional properties of the polymers are similar to those of the native protein. Both show a calciumion-dependent co-operativity of oxygen binding and a Bohr effect. The results suggest that the collar of a hemocyanin molecule has no special function in the process of (co-operative) oxygen binding, different from that of the wall of the molecule.
