Histidine Decarboxylase from Lactobacillus 30a: Nature of Conversion of Proenzyme to Active Enzyme
Indirect evidence led Rodwell (1953) to conclude that histidine decarboxylase from Lactobacillus 30a did not require pyridoxal 5′-phosphate as a coenzyme. This unusual property (Boeker and Snell, 1972), stimulated us to purify the enzyme. Some properties of the homogeneous decarboxylase are shown in Table 1. We found indeed that the enzyme neither contained pyridoxal-P nor depended upon the added coenzyme for activity (Rosenthaler et al., 1965); instead it contained a covalently bound pyruvate residue, combined as an amide at the N-terminus of the larger of two dissimilar subunits (Riley and Snell, 1968, 1970). This pyruvoyl group is essential for catalysis since (1) the enzyme is inhibited by carbonyl reagents and by borohydride reduction, and (2) borohydride reduction in the presence of substrate, followed by acid hydrolysis, permitted isolation of N2-(1-carboxyethyl)histidine (top structure, Fig. 1) and N1(1-carboxyethyl)histamine (bottom, Fig. 1). These data permit formulation of the minimal mechanism for decarboxylase action shown in Figure 1. Appropriate experiments showed that the essential pyruvoyl residue arose without dilution of label from [14C]-serine supplied in the growth medium (Riley and Snell, 1970).
KeywordsPyridoxal Phosphate Histidine Decarboxylase Borohydride Reduction Chymotryptic Digest Histidine Decarboxylase Activity
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- Boeker, E.A., Snell, E.E.: Amino acid decarboxylases. In: The Enzymes, 3rd ed. Boyer, P.D. (ed.). New York-London: Academic Press, 1972, Vol. VI, pp. 217–253Google Scholar
- Rodwell, A.W.: The histidine decarboxylase of a species of Lactobacillus; apparent dispensibility of pyridoxal phosphate as coenzyme. J. Gen. Microbial. 8, 233–237 (1953)Google Scholar