No abstract

Dethiobiotin synthetase (DTBS) catalyzes the penultimate step in biotin biosynthesis, the formation of the ureido ring of dethiobiotin from (7R,8S)-7,8-diaminononanoic acid (7,8-diaminopelargonic acid, DAPA), CO2, and ATP. Solutions of DAPA at neutral pH readily formed a mixture of the N7- and N8-carbamates in the presence of CO2. However, four lines of evidence together indicated that only the N7-carbamate of DAPA was an intermediate in the reaction catalyzed by DTBS. (1) Addition of diazomethane to mixtures of DAPA and [14C]CO2 yielded a mixture of the N7- and N8-methyl carbamate esters, consistent with carbamate formation in free solution. In the presence of excess DTBS (over DAPA), the ratio of N7:N8-methyl carbamate esters recovered was roughly doubled, suggesting that the enzyme preferentially bound the N7-DAPA-carbamate. (2) Both N7- and N8-DAPA-carbamates were observed directly by 1H and 13C NMR in solutions containing DAPA and [13C]CO2. In the presence of excess DTBS (over DAPA) only one carbamate was observed, showing that carbamate binding to the enzyme was regiospecific. 13C NMR of mixtures containing enzyme, [7-15N]DAPA, and [13C]CO2 showed that the enzyme-bound carbamate was at N7 of DAPA. In addition, pulse-chase experiments showed that the binary complex of DTBS and N7-DAPA-carbamate became kinetically committed upon addition of MgATP. (3) The N7-DAPA-carbamate mimic, 3-(1-aminoethyl)nonanedioic acid, in which the carbamate nitrogen was replaced with a methylene group, cyclized to the corresponding lactam in the presence of DTBS and ATP; ADP and P(i) were also formed.(ABSTRACT TRUNCATED AT 250 WORDS)

No abstract

Acyloxylalkyl esters of retinoic acid and small carboxylic acids (C3-5) were evaluated for anticancer activity. The derivative of butyric acid (BA) and all-trans-retinoic acid (ATRA)-retinoyloxymethyl butyrate (RN1)-acting as a mutual prodrug was a more potent inducer of cancer cell differentiation and inhibitor of proliferation than the parent acids. ED50 of RN1 for differentiation induction in HL-60 was over 40-fold lower than that of ATRA. The differentiating activity of ATRA compared to that of the acyloxylalkyl esters derived from butyric (RN1), propionic (RN2), isobutyric (RN3), and pivalic (RN4) acids was found to be: RN1 > RN2 > RN3 > ATRA approximately RN4. This observation implies that the activity of the prodrugs depends on the specific acyl fragment attached to the retinoyl moiety, and the butyroyl fragment conferred the highest potency. The IC50 values for inhibition of Lewis lung (3LLD122) and pancreatic (PaCa2) carcinoma cell line colony formation elicited by RN1 were significantly higher than those of ATRA. In addition to its superiority over ATRA or BA as growth inhibitors of the above cell lines, RN1 was also able to overcome the resistance to ATRA in 3LLD122 cells.