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

Glycine betaine is an organic osmolyte which is often accumulated in response to hyperosmotic stress in euryhaline species. In mitochondria isolated from horseshoe crab (Limulus polyphemus) heart tissue, the synthetic pathway, which is a two step oxidation of choline (choline-->betaine aldehyde-->glycine betaine), appears to be associated with the matrix. The majority of the betaine aldehyde dehydrogenase (BADH) activity, the terminal synthetic enzyme, is found in this subcellular fraction. Partially purified Limulus BADH is highly specific for the substrate betaine aldehyde (K-m of 133 mu M). Two alternative substrates, glyceraldehyde and glycoaldehyde, do not stimulate NAD(+) reduction in the presence of BADH. NAD(+) is an essential co-factor in the oxidation of betaine aldehyde to glycine betaine. Limulus BADH can utilize NADP(+), 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, glycine betaine, competitively inhibits BADH activity. Cations have a profound 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 enzyme, it does not appear that BADH is the rate limiting step in osmotically stimulated glycine betaine synthesis. (C) 1994 Wiley-Liss, Inc.