Iron-binding proteins in vitreous humour.

The soluble protein composition of Macaque monkey vitreous humour was studied in order to understand its iron-binding properties. The protein content of vitreous humour was 217 micrograms/ml +/- 4.6%, 40% of which was serum albumin and 30% an iron-binding protein of hydrodynamic properties identical to that of transferrin or lactoferrin. Relative to serum, the vitreous humour contained a 13-fold excess of this protein(s). Isoelectric focusing, iron-binding and immunoelectrophoretic studies indicated that both vitreous humour and aqueous humour contained lactoferrin as well as serum transferrin. The iron-binding capacity of these proteins in vitreous humour was equivalent to the mass of haemoglobin iron contained in at least 570000 monkey erythrocytes. It was concluded that the intraocular lactoferrin originated from within the eye. These iron-binding proteins may play a protective role in ocular disturbances such as vitreous haemorrhage, iron foreign body toxicity and infection.