The Journal of Biochemistry
Online ISSN : 1756-2651
Print ISSN : 0021-924X
Studies on Regulatory Functions of Malic Enzymes
I. Metabolic Functions of NAD- and NADP-linked Malic Enzymes in Escherichia coli
Tadashi MURAIMasanobu TOKUSHIGEJun NAGAIHirohiko KATSUKI
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1972 Volume 71 Issue 6 Pages 1015-1028

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Abstract

In order to elucidate the metabolic functions of NAD- and NADP- requiring two malic enzymes in Escherichia coil W, various factors controlling the enzyme syntheses and metabolic flow of C4-dicarboxylic acids in the cell were studied.
The NAD-requiring malic enzyme (NAD-enzyme) [EC 1. 1. 1. 38 and 39] was repressed by glucose and induced by malate. The addition of glucose to a malate-containing medium caused a suppression of the enzyme level, but it was overcome by increasing the concentration of malate. On the other hand, the NADP-requiring malic enzyme (NADP-enzyme) [EC 1. 1. 1. 40] was repressed not only by glucose, but also by glycerol, lactate, and acetate in decreasing order of magnitude. Since the reactions to yield acetyl-CoA from the above three compounds via pyruvate are actually irreversible in vivo, acetyl-CoA or acetate was presumed to have a close relation to the repression of the enzyme. However, the concentration of acetyl-CoA in the cell had no correlation with the level of NADP-enzyme and increasing con-centrations of acetate did not exert any marked repression. Although pyruvate exhibited no appreciable repression by itself, combination of pyruvate and acetate exerted a marked repression of the enzyme. In addition, this was found to be the case also with a pyruvate dehydrogenase [EC 1. 2. 4. 1]-less mutant of E. coli. There-fore, the effect of pyruvate was presumed not to be due to conversion of pyruvate into acetyl-CoA or acetate. These results indicate that NAD-enzyme undergoes an induction by malate and NADP-enzyme a concerted repression by acetate and pyru-vate, besides the repression of both enzymes by glucose.
In resting cells of the bacterium grown on the malate medium, the radioactivity was incorporated into fatty acids from 2, 3-14C-succinate but not from 1, 4-14C-suceinate.

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© The Japanese Biochemical Society
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