Hi everybody
Do you know how and by what mecahnism malate can promote lactate uptake by Selenomonas ruminantium? I found the answer below but it does not make any sense to me:
"Some strictly anaerobic bacteria use a reductive or reverse citric acid cycle known as the succinate-propionate pathway to synthesize succinate and(or) propionate (Gottschalk, 1986). Both malate and fumarate are key intermediates in the succinate-propionate pathway, and S. ruminantium uses this pathway (Gottschalk, 1986). The fact that dicarboxylic acids, especially malate and fumarate, stimulate lactate utilization is consistent with the presence of this pathway in this ruminal anaerobe."
Does it make sense to you? Look forward to hearing a great answer.
Ehsan
Dr. Weimer answered me as follows:
Ehsan,
I don't think anyone really knows. I'm not sure if malate directly stimulates just uptake of lactate, or both uptake and utilization. Because malate is converted to succinate via fumarate (a two-step conversion involving dehydration of malate to fumarate, and reduction of fumarate to succinate), it's possible that malate is, in effect, an electron sink for lactate oxidation. Although lactate is typically converted to propionate via acrylate (again, a dehydration followed by a reduction), having malate available as a source of fumarate gives the bacterium another option for disposal of reducing equivalents. This would allow it to convert lactate to acetate and CO2 (via LDH, pyruvate dehydrogenase, PTA and acetate kinase), which could provide more energy via substrate-level phosphorylation but would be difficult to operate unless it could dispose of reducing equivalents generated in the LDH and pyruvate dehydrogenase reactions.
What do you think?
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