The occurrence and properties of 5'-AMP deaminase in dried and toasted nori [Seaweeds]

Crude 5′‐adenylic acid deaminase (5′‐AMP deaminase), extracted from hoshi‐nori (dried nori) and yaki‐nori (toasted nori), was investigated. Substantial activity of 5′‐AMP deaminase was found in the extracts of both dried and toasted nori, but the activity of the latter was lower than the former. The properties of the enzyme were as follows. The optimum pH and optimum temperature were observed in the ranges of pH 7.0–8.0 and 30–50°C, respectively. Metal ions Ca2+ and Sr2+ were most effective on the activation of enzyme, while Cu2+ and Fe2+ did not influence the activity. Ca2+ was also effective for thermal stability of the enzyme. The enzyme activity was comparatively stable even at 50°C in the presence of 0.1 M Ca2+, while it was completely inactivated at 50°C in the absence of Ca2+. The enzyme was specific only to 5′‐AMP. The other adenylic derivatives such as 3′‐AMP, 5′‐ADP, and 5′‐ATP were not reacted. The Km value for 5′‐AMP was estimated to be 2.77 mM. Addition of p‐CMB, an inhibitor of SH‐enzyme, to the reaction mixture inhibited the enzyme activity. Half inhibition was observed with 5 mM p‐CMB concentration. The properties of the enzyme were not essentially different between dried and toasted nori. The activity of the latter was lower than that of the former, and excess toasting (180°C 15 s) caused a remarkable loss of activity.