[Macromolecular spin pH-probes on the basis of human serum albumin]

Human serum albumin has been chemically modified by two different spin pH-sensitive labels of the imidazoline series containing in their structure alkylating and carboxyl groups, respectively. The ESR spectra of spin-labeled proteins are sensitive to pH of the medium. The pK values of spin-labeled proteins measured by the ESR method are: pKI = 3.2 +/- 0.1; pKII = 4.75 +/- 0.1. The resulting macromolecular spin pH probes may be used for measuring the local values of pH by the ESR technique within the pH range of 1.8-6.2.