Fluorescence detection of protein content in house dust: the possible role of keratin.

We propose a fluorescence method for protein content assessment in fine house dust, which can be used as an indicator of the hygienic state of occupied rooms. The results of the measurements performed with 30 house dust samples, including ultrafiltration experiments, strongly suggest that the fluorescence emission of house dust extracts excited at 350 nm is mainly due to protein fragments, which are presumably keratin hydrolysates. This suggestion is supported by several facts: (i) Spectral band shapes for all the samples under investigation are close and correspond to that of keratin; (ii) fluorescence intensity correlates with the total protein content as provided by Lowry assay; (iii) treatment of the samples with proteinase K, which induces keratin hydrolysis, results in fluorescence enhancement without changing fluorescence band shape; and (iv) Raman spectra of keratin and fine house dust samples exhibit a very similar structure. Based on the obtained results and literature data, we propose a hypothesis that keratin is a major substrate for fluorescence species in fine house dust, which are responsible for emission at 350-nm excitation.

Photosystem II Activity of Wild Type Synechocystis PCC 6803 and Its Mutants with Different Plastoquinone Pool Redox States.

To assess the role of redox state of photosystem II (PSII) acceptor side electron carriers in PSII photochemical activity, we studied sub-millisecond fluorescence kinetics of the wild type Synechocystis PCC 6803 and its mutants with natural variability in the redox state of the plastoquinone (PQ) pool. In cyanobacteria, dark adaptation tends to reduce PQ pool and induce a shift of the cyanobacterial photosynthetic apparatus to State 2, whereas illumination oxidizes PQ pool, leading to State 1 (Mullineaux, C. W., and Holzwarth, A. R. (1990) FEBS Lett., 260, 245-248). We show here that dark-adapted Ox(-) mutant with naturally reduced PQ is characterized by slower QA(-) reoxidation and O2 evolution rates, as well as lower quantum yield of PSII primary photochemical reactions (Fv/Fm) as compared to the wild type and SDH(-) mutant, in which the PQ pool remains oxidized in the dark. These results indicate a large portion of photochemically inactive PSII reaction centers in the Ox(-) mutant after dark adaptation. While light adaptation increases Fv/Fm in all tested strains, indicating PSII activation, by far the greatest increase in Fv/Fm and O2 evolution rates is observed in the Ox(-) mutant. Continuous illumination of Ox(-) mutant cells with low-intensity blue light, that accelerates QA(-) reoxidation, also increases Fv/Fm and PSII functional absorption cross-section (590 nm); this effect is almost absent in the wild type and SDH(-) mutant. We believe that these changes are caused by the reorganization of the photosynthetic apparatus during transition from State 2 to State 1. We propose that two processes affect the PSII activity during changes of light conditions: 1) reversible inactivation of PSII, which is associated with the reduction of electron carriers on the PSII acceptor side in the dark, and 2) PSII activation under low light related to the increase in functional absorption cross-section at 590 nm.