Control of 5-aminolaevulinate synthetase activity in Rhodopseudomonas spheroides

Area of Science:

• Microbiology
• Biochemistry

Background:

• Rhodopseudomonas spheroides synthesizes bacteriochlorophyll, a photosynthetic pigment, under low oxygen or anaerobic conditions.
• Bacteriochlorophyll production is significantly reduced under high oxygen tensions.

Purpose of the Study:

• To investigate the regulatory mechanism controlling bacteriochlorophyll synthesis in Rhodopseudomonas spheroides.
• To identify the role of aminolaevulinate synthetase and its activators in response to oxygen levels.

Main Methods:

• Enzyme activity assays for aminolaevulinate synthetase, cystathionase, and rhodanese.
• Measurement of cellular cystine trisulphide levels under varying oxygen conditions.
• Analysis of enzyme kinetics and interconversion between enzyme forms.

Main Results:

• Aminolaevulinate synthetase activity directly correlates with bacteriochlorophyll content, being high in pigmented cells and low in non-pigmented cells.
• Oxygenation of pigmented cells leads to rapid loss of aminolaevulinate synthetase activity and a decrease in cellular cystine trisulphide.
• Cystine trisulphide acts as an endogenous activator for aminolaevulinate synthetase, converting it to a high-activity form.

Conclusions:

• Bacteriochlorophyll synthesis is regulated by oxygen-mediated changes in cystine trisulphide levels, which modulate aminolaevulinate synthetase activity.
• The cellular content of cystine trisulphide, influenced by cystathionase and rhodanese activity, is a key factor in controlling pigment production.
• Oxygenation affects the equilibrium between active and inactive forms of aminolaevulinate synthetase, primarily by inhibiting the activation process.