Possible occurrence for histidyl and cysteyl residues in the catalytic center of rat liver mitochondrial D (-)-beta-hydroxybutyrate dehydrogenase

Alkylation at the active site of the D-3-hydroxybutyrate dehydrogenase (BDH), a membrane phospholipid-dependent enzyme, by 3-chloroacetyl pyridine adenine dinucleotide (3-CAPAD)

The structure of the rat liver's D-3-hydroxybutyrate dehydrogenase (BDH) active site has been investigated using an affinity alkylating reagent, the 3-chloroacetyl pyridine adenine dinucleotide (3-CAPAD). This NAD+ analogue reagent strongly inactivates the enzyme following a concentration- and time-dependent process with a stoichiometry of approximately 1. The reagent reacts at the coenzyme binding site as revealed by the efficient protection by NADH. The effect of 3-CAPAD is stronger with the enzyme into its natural membrane environment than with the lipid-free purified apoBDH or with the reconstituted apoBDH-mitochondrial phospholipid complex. The pH-dependent effect on the inactivation process is in agreement with the participation of protons in the catalytic mechanism of BDH. Furthermore, this study exhibits the phospholipid activating role in BDH catalytic activation.

Comparison of 3-hydroxybutyrate dehydrogenase from bovine heart and rat liver mitochondria

3-Hydroxybutyrate dehydrogenase is a lipid-requiring enzyme with an absolute requirement of phosphatidylcholine for enzymatic activity. Purification of the enzyme to homogeneity from bovine heart mitochondria was described more than a decade ago [H. G. Bock and S. Fleischer (1975) J. Biol. Chem. 250, 5774-5781]. We have modified the purification procedure so that it is faster, the yield has been improved, and the specific activity is greater by approximately 50%. The updated procedure has also been applied to isolate the enzyme from rat liver mitochondria. Characteristics of the enzyme from bovine heart and rat liver mitochondria have been compared and found to be similar with respect to: (1) purification characteristics; (2) amino acid composition; (3) pH optimum for enzymatic activity; (4) kinetic characteristics; (5) molecular weight as determined by sedimentation equilibrium in guanidine hydrochloride; (6) peptide maps; (7) immunological cross-reactivity. These studies show that 3-hydroxybutyrate dehydrogenase from bovine heart and rat liver mitochondria, though similar, are not identical.

Involvement of tyrosyl residues in the structure-function relationships of D-beta-hydroxybutyrate dehydrogenase: a phospholipid-requiring enzyme

The involvement of tyrosyl residues in the function of D-beta-hydroxybutyrate dehydrogenase, a lipid-requiring enzyme, has been investigated by using several tyrosyl modifying reagents, i.e., N-acetylimidazole, a hydrophilic reagent, and 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole and tetranitromethane, two hydrophobic reagents. Modification of the tyrosyl residues highly inactivates the derived enzyme: Treatment of the enzyme with 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole leads to an absorbance at 380 nm and to an incorporation of about 1 mol of 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole per polypeptide chain for complete inactivation. Inactivation by N-acetylimidazole induces a decrease in absorbance at 280 nm which can be reversed by hydroxylamine treatment. On the other hand, the ligands of the active site, such as methylmalonate, a pseudosubstrate, and NAD+ (or NADH), do not protect the enzyme against inactivation. In contrast, the presence of phospholipids strongly protects the enzyme against hydrophobic reagents. Finally, previous modification of the enzyme with N-acetylimidazole does not affect the incorporation of 7-chloro-4-nitro[14C]benzo-2-oxa-1,3-diazole while modification with tetranitromethane does. These results indicate the existence of two classes of tyrosyl residues which are essential for enzymatic activity, and demonstrate their location outside of the active site. One of these residues appears to be located close to the enzyme-phospholipid interacting sites. These essential residues may also be essential for maintenance of the correct active conformation.

Evidence for the presence of one carboxyl group in the catalytic center of D-beta-hydroxybutyrate dehydrogenase. Inactivation and binding studies with carbodiimide reagents

D-beta-Hydroxybutyrate dehydrogenase D-3-hydroxybutyrate: NAD+ oxidoreductase, EC 1.1.1.30), a phosphatidylcholine-requiring enzyme, was irreversibly inactivated by a water-soluble carbodiimide, 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDAC) or a hydrophobic carbodiimide, N,N'-dicyclohexylcarbodiimide (DCCD). The inactivation is pseudo-first-order with a kinetic stoichiometry of about 1. Phospholipid-free apoenzyme was more sensitive towards these reagents than reconstituted phospholipid-enzyme or membrane-bound enzyme forms. Reduced coenzyme (NADH) protected the enzyme against the inactivation, while oxidized coenzyme (NAD+) in presence of 2-methylmalonate (a pseudo-substrate) gave a better protection. It was found that the phospholipid-free apoenzyme bound about 1 mol [14C]DCCD. This incorporation was prevented by EDAC, indicating that both reagents react at the same site. [14C]Glycine ethyl ester, a nucleophilic compound which reacts specifically with the carboxylcarbodiimide derivative was incorporated to the enzyme (1 mol [14C]glycine ethyl ester per polypeptide chain), whatever its form, in the presence of DCCD or EDAC. These results indicate the presence of one carboxyl group probably located at or near the coenzyme-binding site and near the interacting domain of the enzyme with phospholipid.

Modification of arginines in D-beta-hydroxybutyrate dehydrogenase

D-beta-Hydroxybutyrate dehydrogenase (D-3-hydroxybutyrate: NAD+ oxidoreductase, EC 1.1.1.30) is a lipid-dependent enzyme which has an absolute and specific requirement for phosphatidylcholine for function. Chemical derivatization studies using 1,2-cyclohexanedione, an arginine-specific reagent, have been carried out on the purified enzyme devoid of lipid as well as on the enzyme reactivated with phospholipid. Cyclohexanedione inactivated the active enzyme-phospholipid complex and the lipid-free enzyme was rendered inactivatable by phospholipid. From kinetic studies and by direct chemical derivatization studies with [1-14C]cyclohexanedione, we find that incorporation of a single cyclohexanedione molecule per enzyme monomer resulted in complete loss of enzymic activity. The presence of NADH or NAD+, cofactors for the enzyme, offered no protection for the rate of inactivation. The substrates beta-hydroxybutyrate and acetoacetate with or without coenzyme gave little or no protection. However, 2-methyl malonate, a competitive inhibitor for beta-hydroxybutyrate, strongly protected against inactivation. These studies indicate that: (1) a single arginine serves a vital role and is essential for function; (2) the arginine is located in the proximity of the substrate binding site.

Variations of D (-)-beta-hydroxybutyrate dehydrogenase activity of rat liver mitochondria during post-natal development

1. D(-)-beta-hydroxybutyrate dehydrogenase specific activity of rat liver mitochondria changes during ontogenesis: at birth, the activity is low, then increases to a maximum at 12 days, decreases until 50 days to keep constant thereafter. At the same time, mitochondrial protein amount increases regularly while succinatecytochrome c reductase specific activity slightly increases after birth to keep constant afterwards. 2. The observed changes in activity of D(-)-beta-hydroxybutyrate dehydrogenase are not related to possible interactions between the enzyme and phospholids since addition of lecithin to mitochondria does not change the activity. 3. Electrophoresis of mitochondrial proteins isolated from rats at different development stages demonstrates the presence of a protein band characterized by the same electrophoretic mobility as beta-hydroxybutyrate dehydrogenase and by significative changes of its proportion during maturation: the relative amount of this protein increases from the new-born to the 10-12 days old rat, to decrease afterwards. 4. These findings may signify that the increased activity of the enzyme with a maximum at 10-12 days followed by a decrease is related to the rate of the enzymes biosynthesis.