Ultrafiltration as a tool to study binding of copper to salivary proteins

Ultrafiltration may be a good methodology to investigate binding of copper to salivary proteins. However under physiological conditions, copper particulates can also be counted as protein-bound, causing an increased estimate. To examine if ultrafiltration can provide a meaningful result to a salivary protein-copper binding study, copper species in ultrafiltration fractions of saliva were identified and compared to those of control (water). A range 20-40% copper was recovered from retentate of water samples at salivary pH, whilst most copper was filtered out at pH 5.5. Saliva samples showed higher copper retention than water samples at same salivary pH. These results demonstrate that copper particulates were retained with protein-bound copper on ultrafiltration membrane, suggesting that estimate of binding should be interpreted with care.