L-Alanyl-L-Methionine

Thermostable N-acylamino acid racemase from Amycolatopsis sp. TS-1-60, a rare actinomycete strain selected for its ability to grow on agar plates incubated at 40 degrees C, was purified to homogeneity and characterized. The relative molecular mass (M(r)) of the native enzyme and the subunit was estimated to be 300,000 and 40,000 on gel filtration chromatography and sodium dodecyl sulfate-polyacrylamide gel electrophoresis respectively. The isoelectric point (pI) of the enzyme was 4.2. The optimum temperature and pH were 50 degrees C and 7.5 respectively. The enzyme was stable at 55 degrees C for 30 min. The enzyme catalyzed the racemization of optically active N-acylamino acids such as N-acetyl-L- or D-methionine, N-acetyl-L-valine, N-acetyl-L-tyrosine and N-chloroacetyl-L-valine. In addition, the enzyme also catalyzed the racemization of the dipeptide L-alanyl-L-methionine. By contrast, the optically active amino acids, N-alkyl-amino acids and methyl and ethyl ester derivatives of N-acetyl-D- and L-methionine were not racemized. The apparent Km values for N-acetyl-L-methionine and N-acetyl-D-methionine were calculated to be 18.5 mM and 11.3 mM respectively. The enzyme activity was markedly enhanced by the addition of divalent metal ions such as Co2+, Mn2+ and Fe2+ and was inhibited by addition of EDTA and P-chloromercuribenzoic acid. The similarity between the NH2-terminal amino acid sequence of the enzyme and that of Streptomyces atratus Y-53 [Tokuyama et al. (1994) Appl Microbiol Biotechnol 40:835-840] was above 80%.

PTT.119 [p-F-phe-m-bis(2-chloroethyl)amino-L-phe-met ethoxy HCl], a synthetic tripeptide mustard, was evaluated for therapeutic efficacy against a spectrum of childhood rhabdomyosarcomas (RMS) maintained as xenografts in immune-deprived mice. These xenografts were established from previously untreated tumors, and sublines were selected in mice for resistance to L-phenylalanine mustard (L-PAM). PTT.119 caused regression of four of six RMS lines established from untreated tumors, and demonstrated activity similar to that of L-PAM in this model. Against tumors Rh18/L-PAM and Rh28/L-PAM, selected in situ for L-PAM resistance, PTT.119 had no significant activity. Rh28/L-PAM was cross-resistant also to oxazophosphorine mustards (ifosfamide, cyclophosphamide), and both tumors were cross-resistant to adriamycin and vincristine. PTT.119 caused hematologic toxicity similar to that of L-PAM, characterized by a marked decrease in white blood cells and thrombocytopenia.

The side chains of L-alanyl-L-methionine hemihydrate, C(8)H(16)N(2)O(3)S.0.5H(2)O, form hydrophobic columns within a three-dimensional hydrogen-bond network that includes extended polymers of cocrystallized water molecules and C(alpha)-H.S interactions.