CHARACTERIZATION OF PARTIALLY PURIFIED BETAINE ALDEHYDE DEHYDROGENASEFROM HORSESHOE-CRAB (LIMULUS-POLYPHEMUS) CARDIAC MITOCHONDRIA

Glycine betaine is an organic osmolyte which is often accumulated in r esponse to hyperosmotic stress in euryhaline species. In mitochondria isolated from horseshoe crab (Limulus polyphemus) heart tissue, the sy nthetic pathway, which is a two step oxidation of choline (choline-->b etaine aldehyde-->glycine betaine), appears to be associated with the matrix. The majority of the betaine aldehyde dehydrogenase (BADH) acti vity, the terminal synthetic enzyme, is found in this subcellular frac tion. Partially purified Limulus BADH is highly specific for the subst rate betaine aldehyde (K-m of 133 mu M). Two alternative substrates, g lyceraldehyde and glycoaldehyde, do not stimulate NAD(+) reduction in the presence of BADH. NAD(+) is an essential co-factor in the oxidatio n of betaine aldehyde to glycine betaine. Limulus BADH can utilize NAD P(+), although a higher K-m indicates a much lower affinity than that for NAD(+), 267 mu M and 22 mu M, respectively. The end-product, glyci ne betaine, competitively inhibits BADH activity. Cations have a profo und effect on Limulus BADH activity. At physiological concentrations, enzyme activity is stimulated by increases in both [K+] and [Ca2+] but decreased by elevated [Na+]. Although inorganic ions modulate this en zyme, it does not appear that BADH is the rate limiting step in osmoti cally stimulated glycine betaine synthesis. (C) 1994 Wiley-Liss, Inc.