An extremely acidic copper-containing protein from chromaffin granules

Composition of the heme centers in chromaffin granule cytochrome b(561)

Electron paramagnetic resonance and circular dichroism spectra of cytochrome b(561) from chromaffin granule membranes indicated a 2:1 stoichiometry of high- and low-potential hemes. Recombinant bovine cytochrome b(561) expressed in a baculovirus system retained native spectroscopic characteristics and represents a promising model for further study.

Secretory granules from different glands contain neurocuprein-like protein

Secretory granules obtained from bovine pituitary, atrium and adrenal medulla contain an extremely acidic copper protein resembling by its main physico-chemical and antigenic properties as well as by the ability of its apoform to inhibit dopamine beta-monooxygenase the protein from brain, neurocuprein.

On the physiological role of neurocuprein: aponeurocuprein is an inhibitor of dopamine beta-monooxygenase

The apoform of neurocuprein, the copper protein from brain and chromaffin granules, was found to be a potent inhibitor of the hydroxylating activity of dopamine beta-monooxygenase, whereas the holoform of neurocuprein has no effect on the activity of the enzyme. The inhibiting capacity of neurocuprein may be due to the property of the apoprotein to chelate copper from the enzyme. A role of neurocuprein as an endogenous protein regulator of dopamine beta-monooxygenase is suggested.

Osmotic properties of the chromogranins and relation to osmotic pressure in catecholamine storage granules

The soluble proteins (chromogranins) of bovine chromaffin granules have been studied by micro-osmometry with semi-permeable membranes (UM2, PM10 and PM30 with cut-offs greater than 1, greater than 10 and greater than 30 kD, respectively) at 1 = 0.15 and pH 5-8 for protein concentrations up to 20 mg X ml-1. After lysis of chromaffin granules in phosphate buffer pH 6, the released chromogranins behaved as aggregating solutes, consistent with an inconspicuous osmotic pressure contribution from the chromogranins at the protein concentration of the intact granules. Thus, in the presence of phosphate about 90% of the molecules behaved as colloids with Mr = 30,300 at c = o. After lysis in phosphate-free buffers the chromogranins behaved as highly non-ideal solutes in a manner which was incompatible with isotonicity at the protein concentration of the intact granules. About two-thirds of the molecules in the lysates in Na-succinate pH 5-6 and K-acetate pH 6 exhibited Mr = 66,000 and 79,000, respectively. In dilute solutions (less than 12 mg protein X ml-1) and ATP/protein ratios corresponding to those in the intact granules, the UM2 pressures were markedly increased, indicating release of polypeptides with Mr 2000-3000 from aggregates. CaCl2 was without specific effect on the colloid osmotic pressures but reduced the ATP-dependent increase in pressure, suggesting release of molecules twice the size of those released by ATP alone. A model is presented for the contribution of the chromogranins to osmotic pressure regulation in the bovine adrenomedullary catecholamine-storing granules.