Studies of Photochemical Action Spectra on N, N, N', N'-Tetramethyl-p-phenylenediamine-Oxidase-Negative Mutants of Azotobacter vinelandii
Year: 1980
Type: article
Abstract: Studies of photochemical action spectra employing a tunable dye laser as a source of intense monochromatic light were performed on phosphorylating membranes of Azotobacter vinelandii. Two classes of N, N, N′, N′-tetramethyl-p-phenylenediamine-oxidase-negative mutants were used as controls in this study. Class I mutants were found to be blocked between cytochromes c4+c5 and the oxidases, cytochromes o and a1, and class II mutants lacked the c-type cytochromes. For both classes of mutants, cytochrome oxidases o and a1 appeared to be non-functional. Photochemical action spectra of the N, N, N′, N′-tetramethyl-p-phenylenediamine-oxidase-negative mutants were identical to spectra obtained with the parent strain when physiological substrates such as NADH, malate, or succinate were used. Cytochrome d (637 nm) was the only oxidase which exhibited light relief of the carbon-monoxide-inhibited respiration. With reduced Ph(NMe2)2 as substrate, cytochrome o and cytochrome a1, but not cytochrome d exhibited light relief (parent strain only). Cytochrome d, was found to be the least sensitive to the effects of light and the laser power at which one-half maximal light relief occurred (P1/2) was about 68 mW cm−2 at 637 nm. Cytochromes o and a1 were much more sensitive to light having P1/2 values of 3.8 and 13.5 mW cm−2 at 560 and 590 nm, respectively. The P1/2 values appear to reflect differences in the affinity of carbon monoxide for terminal oxidases. This study could not demonstrate by methods using photochemical action spectra that cytochromes o and a1 oxidize physiological substrates under steady-state conditions.
Source: European Journal of Biochemistry
Institutions: University of Memphis, University of Georgia
Language: English
Subfield: Molecular Biology
Domain: Life Sciences
Open Access status: bronze
OpenAlex ID: W2002386858