Ovarian mass causing paradoxical MI and leg ischaemia.

Paradoxical embolus through a patent foramen ovale is a well-reported phenomenon. Clinical consequences include stroke, intestinal infarction, lower limb ischaemia, and even acute myocardial infarction (MI), via embolisation to the coronary arteries. We present a case of acute MI, cardiogenic shock, and cardiac arrest caused not by this mechanism, but by embolisation of thrombotic material to the aortic root with transient complete occlusion of the left main stem (LMS) coronary artery. During percutaneous coronary intervention to treat this occlusion the thrombus became lodged at the aortic bifurcation causing lower limb ischaemia. Despite successful treatment of this via bilateral groin exploration and thromboembolectomy the patient became increasingly acidotic and an abdominal and pelvic CT scan was performed. This revealed the source of the thrombus to be the patient's congested and compressed pelvic veins which were the result of a large, previously undiagnosed ovarian malignancy with metastatic spread. Although very unusual we feel this case highlights an important differential in the diagnosis of anterolateral MI and images similar to those presented here are previously unreported in the literature.

Incidence of contralateral occult inguinal hernia found at the time of laparoscopic trans-abdominal pre-peritoneal (TAPP) repair.

BACKGROUND: Trans-abdominal laparoscopic inguinal hernia repair allows rapid assessment and exploration of the contralateral groin and repair of an occult hernia. Although previous studies have shown that the totally extra-peritoneal (TEP) hernia repair can be used to assess the contralateral groin, there is little data pertaining to the trans-abdominal pre-peritoneal (TAPP) approach. The aim of this study was to document the incidence of occult contralateral hernia at the time of TAPP hernia repair. METHODS: Data were collected prospectively from all patients undergoing laparoscopic TAPP hernia repair in a District General Hospital over a three-year period. Two specialist laparoscopic/upper gastrointestinal surgeons undertook all of the operations and telephone follow-up was carried out by a dedicated laparoscopic specialist nurse. RESULTS: A total of 310 patients underwent hernia surgery. Four cases were excluded, leaving 306 patients in the study. The male:female ratio was 10.5:1, with a median age of 59 years. Two hundred and six (67%) patients were booked for a unilateral hernia repair; of these, a contralateral hernia was found and repaired in 45 (22%). In 76 cases where a bilateral repair was planned, 61 (80%) went on to have both groin defects repaired. In the remaining 20%, the clinical suspicion of bilateral hernia was revised at the time of surgery to unilateral only. Twenty (7%) patients were booked to undergo a unilateral repair with the possibility of a contralateral hernia--in this group, the suspected contralateral defect was confirmed in 6 (30%) cases. Four (1%) cases were booked as femoral repairs, one of which was found to be an inguinal hernia. The clinical diagnostic accuracy was 78%. CONCLUSION: Accurate incidence figures of an occult contralateral inguinal hernia will enhance the pre-operative information given to patients and may impact on resource allocation and planning theatre logistics. Finding and repairing an occult contralateral hernia at the time of TAPP has the distinct advantage that it saves the patient from further symptoms and from another operation with its associated potential morbidity.

The pink pulseless hand: a review of the literature regarding management of vascular complications of supracondylar humeral fractures in children.

Supracondylar fractures of the humerus are the commonest upper limb fractures in children, accounting for up to 70% of all paediatric elbow fractures [Wilson MJ, Hunter JB. Supracondylar fractures of the humerus in children--wire removal in the outpatient setting. Injury Extra 2006 Aug;37(8):313-315] and are often complicated by neurovascular injury. Much confusion surrounds the management of the child with a "pink pulseless hand" post-fracture reduction and several treatment options have been proposed including observation, immediate exploration and angiography. The literature contains a number of case series with variable follow-up. Both angiography and colour duplex ultrasound provide little benefit in the management of these patients. A child with a pink pulseless hand post-fracture reduction can be managed expectantly unless additional signs of vascular compromise develop, in which case exploration should be undertaken.

A transgenic mouse bearing an antisense construct of regulatory subunit type 1A of protein kinase A develops endocrine and other tumours: comparison with Carney complex and other PRKAR1A induced lesions.

BACKGROUND: Inactivation of the human type Ialpha regulatory subunit (RIalpha) of cyclic AMP dependent protein kinase (PKA) (PRKAR1A) leads to altered kinase activity, primary pigmented nodular adrenocortical disease (PPNAD), and sporadic adrenal and other tumours. METHODS AND RESULTS: A transgenic mouse carrying an antisense transgene for Prkar1a exon 2 (X2AS) under the control of a tetracycline responsive promoter (the Tg(Prkar1a*x2as)1Stra, Tg(tTAhCMV)3Uh or tTA/X2AS line) developed thyroid follicular hyperplasia and adenomas, adrenocortical hyperplasia and other features reminiscent of PPNAD, including late onset weight gain, visceral adiposity, and non-dexamethasone suppressible hypercorticosteronaemia, with histiocytic, epithelial hyperplasias, lymphomas, and other mesenchymal tumours. These lesions were associated with allelic losses of the mouse chromosome 11 Prkar1a locus, an increase in total type II PKA activity, and higher RIIbeta protein levels; the latter biochemical and protein changes were also documented in Carney complex tumours associated with PRKAR1A inactivating mutations and chromosome 17 PRKAR1A locus changes. CONCLUSION: We conclude that the tTA/X2AS mouse line with a downregulated Prkar1a gene replicates several of the findings in Carney complex patients and their affected tissues, supporting the role of RIalpha as a candidate tumour suppressor gene.

A pleiomorphic GH pituitary adenoma from a Carney complex patient displays universal allelic loss at the protein kinase A regulatory subunit 1A (PRKARIA) locus.

Carney complex (CNC) is a familial multiple endocrine neoplasia syndrome associated with GH-producing pituitary tumours and transmitted as an autosomal dominant trait. Mutations of the PRKAR1A gene are responsible for approximately half the known CNC cases but have never found in sporadic pituitary tumours. Pituitary tissue was obtained from an acromegalic CNC patient heterozygote for a common (PRKARIA)i-inactivating mutation. Both immunohistochemistry and electron microscopy showed a highly pleiomorphic pituitary adenoma. The cell culture population appeared morphologically heterogeneous and remained so after more than 30 passages. The mixture was comprised of cells strongly immunostained for GH, spindle-shaped myofibroblast-like cells, and cuboid cells with large axonal projections (negative for GH). The population appeared to have both epithelial and mesenchymal cells. Both at baseline and at passage 30, cytogenetic analysis indicated the presence of normal 46, XY diploid karyotype, whereas losses of the PRKARIA(i) locus were demonstrated in more than 98% of the cells by fluorescent in situ hybridisation, supporting this gene's involvement in pituitary tumorigenesis. Allelic loss may have occurred in a single precursor cell type that differentiated and clonally expanded into several phenotypes. Epithelial-to-mesenchymal transition may also occur in CNC-associated pleiomorphic pituitary adenomas.

Protein kinase A and its role in human neoplasia: the Carney complex paradigm.

The type 1 alpha regulatory subunit (R1alpha) of cAMP-dependent protein kinase A (PKA) (PRKAR1A) is an important regulator of the serine-threonine kinase activity catalyzed by the PKA holoenzyme. Carney complex (CNC) describes the association 'of spotty skin pigmentation, myxomas, and endocrine overactivity'; CNC is in essence the latest form of multiple endocrine neoplasia to be described and affects the pituitary, thyroid, adrenal and gonadal glands. Primary pigmented nodular adrenocortical disease (PPNAD), a micronodular form of bilateral adrenal hyperplasia that causes a unique, inherited form of Cushing syndrome, is also the most common endocrine manifestation of CNC. CNC and PPNAD are genetically heterogeneous but one of the responsible genes is PRKAR1A, at least for those families that map to 17q22-24 (the chromosomal region that harbors PRKAR1A). CNC and/or PPNAD are the first human diseases to be caused by mutations in one of the subunits of the PKA holoenzyme. Despite the extensive literature on R1alpha and PKA, little is known about their potential involvement in cell cycle regulation, growth and/or proliferation. The presence of inactivating germline mutations and the loss of its wild-type allele in CNC lesions indicated that PRKAR1A could function as a tumor-suppressor gene in these tissues. However, there are conflicting data in the literature about PRKAR1A's role in human neoplasms, cancer cell lines and animal models. In this report, we review briefly the genetics of CNC and focus on the involvement of PRKAR1A in human tumorigenesis in an effort to reconcile the often diametrically opposite reports on R1alpha.

Identification of peroxisome proliferator-responsive human genes by elevated expression of the peroxisome proliferator-activated receptor alpha in HepG2 cells.

In mice and other sensitive species, PPARalpha mediates the induction of mitochondrial, microsomal, and peroxisomal fatty acid oxidation, peroxisome proliferation, liver enlargement, and tumors by peroxisome proliferators. In order to identify PPARalpha-responsive human genes, HepG2 cells were engineered to express PPARalpha at concentrations similar to mouse liver. This resulted in the dramatic induction of mRNAs encoding the mitochondrial HMG-CoA synthase and increases in fatty acyl-CoA synthetase (3-8-fold) and carnitine palmitoyl-CoA transferase IA (2-4-fold) mRNAs that were dependent on PPARalpha expression and enhanced by exposure to the PPARalpha agonist Wy14643. A PPAR response element was identified in the proximal promoter of the human HMG-CoA synthase gene that is functional in its native context. These data suggest that humans retain a capacity for PPARalpha regulation of mitochondrial fatty acid oxidation and ketogenesis. Human liver is refractory to peroxisome proliferation, and increased expression of mRNAs for the peroxisomal fatty acyl-CoA oxidase, bifunctional enzyme, or thiolase, which accompanies peroxisome proliferation in responsive species, was not evident following Wy14643 treatment of cells expressing elevated levels of PPARalpha. Additionally, no significant differences were seen for the expression of apolipoprotein AI, AII, or CIII; medium chain acyl-CoA dehydrogenase; or stearoyl-CoA desaturase mRNAs.

Peroxisome proliferator activated receptor-alpha expression in human liver.

The peroxisome proliferator activated receptor alpha (PPAR) is a member of the steroid/hormone receptor superfamily that mediates the peroxisome proliferator-dependent transcriptional activation of genes encoding several peroxisomal and microsomal enzymes as well as peroxisome proliferation. Human liver is refractory to the pathological effects of peroxisome proliferators that are seen in mice. With the use of RNase protection assays, the ratio of hepatic PPAR alpha mRNA to beta-actin mRNA was found to be 1 order of magnitude lower in humans than that observed in mice. In addition, the isolation of human cDNA for PPAR alpha that does not encode a functional PPAR because it lacks exon 6 as a result of alternate RNA splicing suggested that this process might also diminish the expression of PPAR alpha. RNase protection analysis of total RNA revealed the presence of splice variants lacking exon 6 at significant levels in all 10 human liver samples examined. Supershift analysis using the CYP4A6-Z peroxisome proliferator response element and antisera specific for PPAR alpha revealed easily detectable amounts of PPAR alpha DNA binding activity in mouse liver lysates, whereas human liver lysates contained > 10-fold lower amounts of PPAR alpha DNA binding activity. In contrast to mouse lysates, the amount of PPAR alpha binding in human lysates was generally less than that of other unidentified proteins. These results suggest that although humans retain the coding potential for a functional receptor, the low levels of PPAR alpha expression in liver may be insufficient to compete effectively with other proteins that bind to peroxisome proliferator response elements.

alphaT244M mutation affects the redox, kinetic, and in vitro folding properties of Paracoccus denitrificans electron transfer flavoprotein.

Threonine 244 in the alpha subunit of Paracoccus denitrificans transfer flavoprotein (ETF) lies seven residues to the amino terminus of a proposed dinucleotide binding motif for the ADP moiety of the FAD prosthetic group. This residue is highly conserved in the alpha subunits of all known ETFs, and the most frequent pathogenic mutation in human ETF encodes a methionine substitution at the corresponding position, alphaT266. The X-ray crystal structures of human and P. denitrificans ETFs are very similar. The hydroxyl hydrogen and a backbone amide hydrogen of alphaT266 are hydrogen bonded to N(5) and C(4)O of the flavin, respectively, and the corresponding alphaT244 has the same structural role in P. denitrificans ETF. We substituted a methionine for T244 in the alpha subunit of P. denitrificans ETF and expressed the mutant ETF in Escherichia coli. The mutant protein was purified, characterized, and compared with wild type P. denitrificans ETF. The mutation has no significant effect on the global structure of the protein as inferred from visible and near-ultraviolet absorption and circular dichroism spectra, far-ultraviolet circular dichroism spectra, and infrared spectra in 1H2O and 2H2O. Intrinsic fluorescence due to tryptophan of the mutant protein is 60% greater than that of the wild type ETF. This increased tryptophan fluorescence is probably due to a change in the environment of the nearby W239. Tyrosine fluorescence is unchanged in the mutant protein, although two tyrosine residues are close to the site of the mutation. These results indicate that a change in structure is minor and localized. Kinetic constants of the reductive half-reaction of ETF with porcine medium chain acyl-CoA dehydrogenase are unaltered when alphaT244M ETF serves as the substrate; however, the mutant ETF fails to exhibit saturation kinetics when the semiquinone form of the protein is used as the substrate in the disproportionation reaction catalyzed by P. denitrificans electron transfer flavoprotein-ubiquinone oxidoreductase (ETF-QO). The redox behavior of the mutant ETF was also altered as determined from the equilibrium constant of the disproportionation reaction. The separation of flavin redox potentials between the oxidized/semiquinone couple and semiquinone/hydroquinone couple are -6 mV in the wild type ETF and -27 mV in the mutant ETF. The mutation does not alter the AMP content of the protein, although the extent and fidelity of AMP-dependent, in vitro renaturation of the mutant AMP-free apoETF is reduced by 57% compared to renaturation of wild type apoETF, likely due to the absence of the potential hydrogen bond donor T244.

Targeted antipeptide antibodies to cytochrome P450 2C18 based on epitope mapping of an inhibitory monoclonal antibody to P450 2C51.

The epitope recognized by the inhibitory monoclonal antibody designated 2F5, which was raised against P450 2C5, was mapped to amino acids 237-260 by immunoblotting using a combination of recombinant antigens and chimeric and partial fusion proteins constructed from rabbit P450s 2C2, 2C4, 2C5, and 2C16, which are recognized by 2F5, and from 2C1 and 2C3, which are not. When the sequence of the epitope for 2F5 (amino acids 237-260) was compared with those of other rabbit 2C P450s, a single lysine residue at position 253 appeared to be a likely determinant of 2F5 immunoreactivity. Substitution of lysine for glutamic acid 253 in P450 2C3 (2C3E253K) conferred immunoreactivity and the ability of 2F5 to inhibit progesterone metabolism catalyzed by P450 2C3E253K. Sequence alignment revealed that this epitope lies in close proximity to the epitope identified for LKM-1 autoantibodies to P450 2D6. Based on these results, an antipeptide antibody was raised to the corresponding region (amino acids 252-263) of human P450 2C18. The resulting antipeptide antiserum recognizes P450 2C18 but not P450 2C8, 2C9, or 2C19. However, the antipeptide 2C18 antiserum did not inhibit 2C18-catalyzed diazepam N-demethylation. Human 2C P450s were also quantitated by immunoblot analysis in a panel of six human liver microsomes using Escherichia coli expressed P450s as standards. Analysis of immunoblots indicated that, if present, P450 2C18 was expressed at very low levels (<2.5 pmol/mg), whereas P450s 2C8, 2C9, and 2C19 were easily detected.

Helcococcus kunzii as sole isolate from an infected sebaceous cyst.

Helcococcus kunzii was isolated in pure culture from pus drained from an infected sebaceous cyst associated with marked cellulitis. The cyst was excised one month later after the inflammation had subsided with flucloxacillin treatment. This is the first report of the isolation of H. kunzii as the sole pathogen from an infected site.

A single amino acid substitution confers progesterone 6 beta-hydroxylase activity to rabbit cytochrome P450 2C3.

A cDNA encoding a naturally occurring variant of cytochrome P450 (P450) 2C3 that catalyzes the 6 beta- and 16 alpha-hydroxylation of progesterone exhibits six differences of nucleotide sequence leading to five amino acid substitutions from that encoding 2C3, a progesterone 16 alpha-hydroxylase that does not catalyze 6 beta-hydroxylation. Analysis of chimeric and mutant enzymes indicates that a Ser/Thr difference at position 364 underlies the difference between the two enzymes in 6 beta-hydroxylase activity as well as sensitivity to the inhibitor, 16 alpha-methylprogesterone. In addition, an Ile/Met difference at position 178 influences the apparent Km for progesterone. The two mutations, S364T and 1178M, together convert 2C3 to a form that exhibits kinetic properties which are similar to the 2C3v enzyme, and the reciprocal mutations in 2C3v convert it to an enzyme that resembles 2C3. Interestingly, position 364 of 2C3 maps to a substrate-contacting domain suggested by models for mammalian P450 enzymes based on the structure of P450cam. Ile178 is highly conserved among mammalian microsomal P450s with the exception of CYP4A and CYP19 enzymes which exhibit a Met at this alignment position.

LKM-1 autoantibodies recognize a short linear sequence in P450IID6, a cytochrome P-450 monooxygenase.

LKM-1 autoantibodies, which are associated with autoimmune chronic active hepatitis, recognize P450IID6, a cytochrome P-450 monooxygenase. The reactivities of 26 LKM-1 antisera were tested with a panel of deletion mutants of P450IID6 expressed in Escherichia coli. 22 sera recognize a 33-amino acid segment of P450IID6, and 11 of these recognize a shorter segment, DPAQPPRD. PAQPPR is also found in IE175 of herpes simplex virus type 1 (HSV-1). Antibodies for HSV-1 proteins were detected by ELISA in 17 of 20 LKM-1 sera tested. An immobilized, synthetic peptide, DPAQPPRDC, was used to purify LKM-1 antibodies. Affinity purified LKM-1 autoantibodies react on immunoblots with a protein in BHK cells after infection with HSV-1. 11 of 24 LKM-1 sera, including 3 that recognize DPAQPPRD, also exhibit antibodies to the hepatitis C virus (HCV) protein, C100-3. Affinity purified LKM-1 antibodies did not recognize C100-3. However, partial sequence identity was evident between portions of the immunopositive 33-amino acid segment of P450IID6 and other portions of the putative HCV polyprotein. Immune cross-recognition of P450IID6 and HCV or HSV-1 proteins may contribute to the occurrence of LKM-1 autoantibodies.

Major antigen of liver kidney microsomal autoantibodies in idiopathic autoimmune hepatitis is cytochrome P450db1.

Type 1, liver kidney microsomal autoantibodies (LKM-1) are associated with a subgroup of idiopathic autoimmune type, chronic active hepatitis (CAH). The antigenic specificity of LKM-1 autoantibodies from 13 patients was investigated by immunoblot analysis of human liver microsomal proteins. Polypeptides of 50, 55, and 64 kD were detected with these antisera. A high titer LKM-1 serum was selected to screen a human liver lambda gt11 cDNA expression library, resulting in the isolation of several complementary (c)DNA clones. Autoantibodies affinity purified from proteins expressed by two of the immunopositive cDNA clones, HLD8.2 and HLD13.2, specifically react with a 50-kD protein of human liver microsomes and display immunofluorescence staining of the proximal renal tubular epithelia characteristic of LKM-1 sera. Determination of the sequence of HLD8.2 revealed that it encodes a recently described cytochrome P450db1. A bacterial fusion protein constructed from HLD8.2 proved to be a specific and sensitive diagnostic reagent. All sera from patients with LKM-1 positive liver disease react with this fusion protein. No reaction was seen, however, for sera from patients with other types of autoimmune liver diseases, viral hepatitis, systemic immunological disorders, or healthy controls.

Intraspecies individuality for the metabolism of steroids.

A variety of regulatory factors contribute to differences in the rates of 6 beta-hydroxylation, 16 alpha-hydroxylation and 21-hydroxylation of progesterone as catalysed by liver microsomes prepared from individual rabbits. It is likely that the 6 beta-hydroxylation of progesterone is catalysed primarily by cytochrome P-450 3c, an enzyme that exhibits allosteric activation by alpha-napthoflavone, and by a form of P-450 3b, 6 beta+, that is expressed in some rabbits in an autosomal dominant manner. The mechanism of activation for P-450 3c appears to reflect an effector mediated increase of the affinity of the enzyme for substrate as judged by substrate binding studies. A second form of P-450 3b, 6 beta-, catalyses a major portion of hepatic progesterone 16 alpha-hydroxylation and exhibits activation by a variety of C21 steroids of which 5 beta-pregnane-3 beta,20 alpha-diol is the most efficacious. P-450 1, which catalyses the 21-hydroxylation of progesterone, is expressed at 10-fold higher levels in the 21H phenotype than the 21L phenotype, and the former is inherited as an autosomal dominant characteristic. A cDNA encoding a P-450 1-related gene product exhibits a predicted amino acid sequence that is 95% homologous to that of P-450 1. The P-450 1-related gene product is expressed in liver to a similar degree in both 21H and 21L rabbits.

Cloning and characterization of cDNAs encoding 2,3,7,8-tetrachlorodibenzo-p-dioxin-inducible rabbit mRNAs for cytochrome P-450 isozymes 4 and 6.

Monoclonal antibodies toward rabbit liver cytochrome P-450 isozyme 6 (P-450 6) were used to identify several recombinant clones from a pBR322 cDNA library that express beta-lactamase-P-450 6 hybrid proteins. The nucleic acid sequence and predicted amino acid sequence of a rabbit P-450 6 cDNA shows a high degree of homology with rat P-450c and mouse P1-450. When used as a probe to rescreen the library, the P-450 6 cDNA hybridized to several heterologous classes of cDNAs. One such class was shown to encode P-450 4 by comparison of its predicted amino acid sequence to amino acid sequences of cysteine-containing tryptic peptides derived from P-450 4. DNA sequence analysis of a cDNA clone belonging to a third class demonstrated that it contained a 131-base-pair intervening sequencing when compared to the cDNA coding for P-450 6. This sequence corresponds in location to intron E of the rat P-450c gene. Blot-hybridization analysis demonstrated that 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) dramatically induced P-450 4 and 6 mRNAs, which differ in size. The sizes of these mRNAs differ from their analogs in the mouse as a result of divergence in the 3' untranslated portions of the mRNAs.

Use of a monoclonal antibody specific for rabbit microsomal cytochrome P-450 3b to characterize the participation of this cytochrome in the microsomal 6 beta- and 16 alpha-hydroxylation of progesterone.

A monoclonal antibody was developed that is specific for the 3b electrophoretic class of rabbit liver microsomal cytochrome P-450 as judged by immunoprecipitation and subsequent electrophoretic analysis. The antibody is inhibitory of catalytically distinct, variant forms of P-450 3b prepared from New Zealand White or IIIVO/J rabbits, respectively. Peptide mapping of the immunopurified P-450 3b from NZW and IIIVO/J microsomes indicates that a characteristic difference between the variant forms is exhibited by the antigen. In addition, a competitive assay indicates that the binding properties of the antibody do not differ substantially toward the variant forms of P-450 3b. The inhibitory antibody was used to examine the contribution of P-450 3b to the microsomal 16 alpha- and 6 beta-hydroxylation of progesterone. The antibody inhibits 40-70% of the 16 alpha-hydroxylase activity of microsomes from either New Zealand White or IIIVO/J rabbits. In contrast, it does not inhibit 6 beta-hydroxylation catalyzed by microsomes prepared from strain IIIVO/J but does inhibit this reaction as catalyzed by microsomes from most New Zealand White rabbits. The antibody also inhibits the increased 16 alpha-hydroxylase activity of IIIVO/J microsomes observed in the presence of 5 beta-pregnane-3 beta,20 alpha-diol, an allosteric effector of this variant form of P-450 3b. Use of this monoclonal antibody provides a link between the observed properties of the purified, variant forms of P-450 3b and microsomal metabolism. These results indicate that the antibody can be used to phenotype variant forms of P-450 3b in microsomal fractions.

Three monoclonal antibodies to rabbit microsomal cytochrome P-450 1 recognize distinct epitopes that are shared to different degrees among other electrophoretic types of cytochrome P-450.

Three monoclonal antibodies, 1F11, 1G11, and 2F5, were developed toward rabbit microsomal cytochrome P-450 1. Each was linked to Sepharose in order to indirectly immunoprecipitate microsomal proteins. All three antibodies bind polypeptides from solubilized microsomes that exhibit the same electrophoretic mobility as P-450 1. However, 2F5 recognizes an additional microsomal protein that exhibits a relative electrophoretic mobility between that of P-450 1 and 3b that does not appear to be P-450 2. 1G11 also reacts with several microsomal proteins that include both P-450 1 and P-450 3b. These results indicate that at least three electrophoretically distinct forms of microsomal P-450 share one or more antigenic determinants with P-450 1. Binding studies demonstrate that each antibody can react independently with P-450 1, indicating that the three antigenic determinants recognized by the respective monoclonal antibodies are spatially distinct and nonoverlapping. Reconstituted P-450 1 isolated from rabbit liver microsomes that exhibit 10-fold higher progesterone 21-hydroxylase than most preparations of liver microsomes obtained from outbred New Zealand White rabbits catalyzes this reaction with relatively high rates compared to that exhibited by microsomes or to that catalyzed by five electrophoretically distinct forms of P-450. Both the 1F11 and 2F5 antibodies extensively inhibit the liver microsomal 21-hydroxylation of progesterone. When the 1F11 antibody is used to indirectly immunoprecipitate the antigens it recognizes in microsomes displaying a high rate of progesterone 21-hydroxylase activity, a single electrophoretic band corresponding in mobility to P-450 1 was observed.