No abstract

Arthrobacter oxydans P52 isolated from soil samples was found to degrade the phenylcarbamate herbicides phenmedipham and desmedipham cometabolically by hydrolyzing their central carbamate linkages. The phenylcarbamate hydrolase (phenmedipham hydrolase) responsible for the degradative reaction was purified to homogeneity. The enzyme was shown to be a monomer with a molecular weight of 55,000. A 41-kb wild-type plasmid (pHP52) was identified in A. oxydans P52, but not in a derivative of this strain that had spontaneously lost the ability to hydrolyze phenylcarbamates, indicating that the gene for phenylcarbamate degradation (pcd) is plasmid encoded. Determination of two partial amino acid sequences allowed the localization of the coding sequence of the pcd gene on a 3.3-kb PstI restriction fragment within pHP52 DNA by hybridization with synthetic oligonucleotides. The phenylcarbamate hydrolase was functionally expressed in Escherichia coli under control of the lacZ promoter after the 3.3-kb PstI fragment was subcloned into the vector pUC19. A stretch of 1,864 bases within the cloned Pst fragment was sequenced. Sequence analysis revealed an open reading frame of 1,479 bases containing the amino acid partial sequences determined for the purified enzyme. Sequence comparisons revealed significant homology between the pcd gene product and the amino acid sequences of esterases of eukaryotic origin. Subsequently, it was demonstrated that the esterase substrate p-nitrophenylbutyrate is hydrolyzed by phenmedipham hydrolase.

The saliva of D. rotundus contains at least four plasminogen activators (PAs) which all require fibrin as a cofactor. D. rotundus salivary PAs (DSPAs) exhibit a sequential array of structural motifs such as "Finger" (F), "EGF" (E), "Kringle" (K) and "Protease" (P) which was elucidated by cDNA cloning and sequencing. The respective domain organizations are: FEKP (DSPA alpha 1 and DSPA alpha 2), EKP (DSPA beta) and KP (DSPA gamma). In all four forms the plasmin-sensitive site of tPA is obliterated, indicating that they function as single-chain enzymes. DSPA alpha 1 differs from alpha 2 by amino acid substitutions found mainly in the F, E and K domain, 11% of the total sequence. DSPA beta and gamma, while being closely related to alpha 2, still exhibit 2 and 13 amino acid exchanges, respectively. These sequence heterogeneities, together with results of Southern blot hybridization experiments, strongly suggest that the four DSPA mRNA species originate from different genes. All four forms of DSPA have been expressed in animal cell culture and DSPA alpha 1 was chosen for a detailed pharmacological characterization. In vitro DSPA alpha 1 activity is enhanced 50,000-fold in the presence of fibrin, whereas the activity of single chain tPA is only enhanced 100-fold. At equally effective thrombolytic doses DSPA causes lower bleeding incidence in a rat mesenteric vein model and exhibits high potency, clot selectivity, and speed in the dissolution of fibrin embolized into the lung of anesthetized rats. In the copper coil-induced dog coronary heart infarction model, at doses that achieve patency at equal rates, reocclusion is significantly less frequent than with tPA. These results indicate that DSPA alpha 1 may be a safer and more efficacious thrombolytic agent than the PAs currently in clinical use.

Steroid hydroxylation specificities were determined for the wild-type and the two allelic variants of the polymorphic human cytochrome P450 1A1 (CYP1A1) that were associated with amino acid exchanges near the active site of the enzyme. All three variants were expressed in insect cells using recombinant baculoviruses. Each variant protein was spectrally and enzymatically active, as judged by the ability of the prepared microsomes to catalyse O-dealkylation of ethoxyresorufin and pentoxyresorufin in cumene hydroperoxide-mediated reactions. With progesterone and testosterone as substrate, all variants of CYP1A1 exhibited high, but different steroid hydroxylation activities (8-40 pmol hydroxysteroid/min/pmol CYP1A1, i.e. approximately 800-4000 pmol/min/mg microsomal protein). All three variants exclusively catalysed 6beta-hydroxylation of both steroids. In addition, towards progesterone as substrate, all variants also catalysed 16alpha-hydroxylations with approximately half of the rate of 6beta-hydroxylation activity. With progesterone as substrate for hydroxylation in 6beta position, CYP1A1 T461N had the lowest catalytic efficiency (Vmax/Km) followed by the CYP1A1 I462V variant and the wild-type enzyme. For 16alpha-hydroxylation of progesterone, the catalytic efficiencies of the three variants are not statistically significantly different. With testosterone as substrate the CYP1A1 1462V variant catalysed 6beta-hydroxylation with an efficiency considered not significantly different compared to the wild-type, although both the apparent Km and Vmax were significantly decreased. In contrast, the CYP1A1 T461N variant exhibited significantly decreased catalytic efficiencies compared to both the 1462V variant and the wild-type enzyme. These results indicate that all three naturally occurring allelic variants of human CYP1A1 hydroxylate steroid hormones with varying efficiencies in a stereo- and regioselective manner, whereby the CYP1A1 T461N variant exhibited the lowest catalytic efficiency.

A 4.3 kb EcoRI fragment carrying the gene for cytochrome P450meg, the steroid-15 beta-monooxygenase from Bacillus megaterium ATCC 13368, was cloned and completely sequenced. The gene codes for a protein of 410 amino acids and was expressed in Escherichia coli and B. subtilis. Protein extracts from the recombinant E. coli strains were able to hydroxylate corticosteroids in the 15 beta position when supplemented with an extract from a P450- mutant of B. megaterium ATCC 13368 as a source of megaredoxin and megaredoxin reductase. In contrast, 15 beta-hydroxylation was obtained in vitro and in vivo without the addition of external electron transfer proteins, when cytochrome P450meg was produced in B. subtilis 168. Protein extracts from nonrecombinant B. subtilis 168 could also support the in vitro hydroxylation by cytochrome P450meg produced in E. coli.