1-Aminocyclopropane-1-carboxylate (ACC) Deaminase Induced by ACC Synthesized and Accumulated inPenicillium citrinumIntracellular Spaces

We have already described how 1-aminocyclopropane-1-carboxylic acid (ACC), which is a precursor of the plant hormone ethylene, is synthesized in Penicillium citrinum through the same reaction by the catalysis of ACC synthase [EC 4.4.1.14] as in higher plants. In addition, ACC deaminase [EC 4.1.99.4], which degrades ACC to 2-oxobutyrate and ammonia, was also purified from this strain. To study control of induction of ACC deaminase in this organism, we have isolated and analyzed the cDNA of P. citrinum ACC deaminase and studied the expression of ACC deaminase mRNA in P. citrinum cells. By the analysis of peptides from the digests of the purified and modified ACC deaminase with lysylendopeptidase, 70 % of its amino acid sequences were obtained. These amino acid sequences were used to identify a cDNA, consisting of 1,233 bp with an open reading frame of 1,080 bp encoding ACC deaminase with 360 amino acids. The deduced amino acids from the cDNA are identical by 52% and 45% to those of enzymes of Pseudomonas sp. ACP and Hansenula saturnus. Through Northern blot analysis, we found that the mRNA of ACC deaminase was expressed in P. citrinum cells grown in a medium containing 0.05% L-methionine. These findings suggest that ACC synthesized by ACC synthase and accumulated in P. citrinum intracellular spaces can induce the ACC deaminase that degrades the ACC.