Heparin Does Not Regulate Circulating Human PCSK9 (Proprotein Convertase Subtilisin-Kexin Type 9) in a General Population-Brief Report

BACKGROUND

PCSK9 (proprotein convertase subtilisin-kexin type 9) chaperones the hepatic LDLR (low-density lipoprotein receptor) for lysosomal degradation, elevating serum LDL (low-density lipoprotein) cholesterol and promoting atherosclerotic heart disease. Though the major effect on the hepatic LDLR comes from secreted PCSK9, the details of PCSK9 reuptake into the hepatocyte remain unclear. In both tissue culture and animal models, HSPGs (heparan sulfate proteoglycans) on hepatocytes act as co-receptors to promote PCSK9 reuptake. We hypothesized that if this PCSK9:HSPG interaction is important in humans, disrupting it with unfractionated heparin (UFH) would acutely displace PCSK9 from the liver and increase plasma PCSK9.

METHODS

We obtained remnant plasma samples from 160 subjects undergoing cardiac catheterization before and after administration of intravenous UFH. PCSK9 levels were determined using a commercial enzyme-linked immunosorbent assay.

RESULTS

Median plasma PCSK9 was 113 ng/mL prior to UFH and 119 ng/mL afterward. This difference was not significant (P=0.83 [95% CI, -6.23 to 6.31 ng/mL]). Equivalence testing provided 95% confidence that UFH would not raise plasma PCSK9 by > 4.7%. Among all subgroups, only subjects with the lowest baseline PCSK9 concentrations exhibited a response to UFH (8.8% increase, adj. P=0.044). A modest correlation was observed between baseline plasma PCSK9 and the change in plasma PCSK9 due to UFH (RS=-0.3634; P<0.0001).

CONCLUSIONS

Administration of UFH does not result in a clinically meaningful effect on circulating PCSK9 among an unselected population of humans. The results cast doubt on the clinical utility of disrupting the PCSK9:HSPG interaction as a general therapeutic strategy for PCSK9 inhibition. However, the observations suggest that in selected populations, disrupting the PCSK9:HSPG interaction could still affect PCSK9 reuptake and offer a therapeutic benefit.

Echocardiographic determination of pulmonary arterial capacitance

A growing body of evidence has demonstrated that pulmonary arterial capacitance (PAC) is the strongest hemodynamic predictor of clinical outcomes across a wide spectrum of cardiovascular disease, including pulmonary hypertension and heart failure. We hypothesized that a ratio of right ventricular stroke volume (RVOT VTI) to the associated peak arterial systolic pressure (PASP) could function as a reliable non-invasive surrogate for PAC. We performed a prospective study of patients undergoing simultaneous transthoracic echocardiography and right heart catheterization (RHC) for various clinical indications. Measurements of the RVOT VTI/PASP ratio from echocardiographic measurements were compared against PAC calculated from RHC measurements. Correlation coefficients and Bland-Altman analysis compared the RVOT VTI/PASP ratio with PAC. Forty-five subjects were enrolled, 38% were female and mean age was 54 years (SD 13 years). The reason for referral to RHC was most commonly post-heart transplant surveillance (40%), followed by heart failure (22%), and pulmonary hypertension (18%). Pre-capillary pulmonary hypertension was present in 18%, isolated post-capillary pulmonary hypertension was present in 13%, and combined pre-and post-capillary pulmonary hypertension was present in 29%. The RVOT VTI/PASP ratio was obtainable in the majority of patients (78%), and Pearson's correlation demonstrated moderately-strong association between PAC and the RVOT VTI/PASP ratio, r = 0.75 (P < 0.001). Bland-Altman analysis demonstrated good agreement between measurements without suggestion of systematic bias and a mean difference in standardized units of - 0.133. In a diverse population of patients and hemodynamic profiles, we validated that the ratio of RVOT VTI/PASP to be a reliably-obtained non-invasive marker associated with PAC.

Long-term outcomes of angiographically confirmed coronary stent thrombosis: results from a multicentre California registry

AIMS

Limited data exist on long-term outcomes of patients with stent thrombosis (ST). Our aim was to describe the long-term outcomes after angiographically confirmed ST.

METHODS AND RESULTS

In this multicentre registry, consecutive cases of definite ST were identified between 2005 and 2013. Clinical and procedural characteristics, in-hospital outcomes and long-term survival up to five years were compared between those with and those without adverse cardiovascular and cerebrovascular events (MACCE), defined as all-cause mortality, myocardial infarction and stroke. Two hundred and twenty-one patients with 239 stent thrombosis events were identified. Patients who developed MACCE were older, less likely to be men, and less likely to have hypertension. Angiographic characteristics were similar. Patients who had a MACCE event showed a trend towards a lower likelihood of procedural success (86% vs. 91%, p=0.05). MACCE rates were 22% at one year and 41% at five years. All-cause mortality was 13% at one year and 24% at five years. On multivariable analysis, age, diabetes mellitus, active smoking and ST at a bifurcation were independently associated with the occurrence of MACCE up to five years.

CONCLUSIONS

Age, active smoking, diabetes mellitus and bifurcation disease are independently associated with long-term MACCE over a five-year follow-up period.

Angiographically confirmed stent thrombosis in contemporary practice: insights from intravascular ultrasound

OBJECTIVE

We hypothesized that patients presenting with stent thrombosis (ST) have a high prevalence of stent underexpansion and malapposition when assessed by intravascular ultrasound (IVUS).

BACKGROUND

IVUS can provide mechanistic insight into mechanical factors, including stent underexpansion, malapposition, and fracture that may predispose to ST.

METHODS

All consecutive cases of angiographically confirmed ST from a multicenter registry (from 2005 to 2010) were reviewed. All IVUS images were reviewed off-line for the presence of stent underexpansion, malapposition, and fracture. Kaplan-Meier analysis was used to determine whether use of IVUS at the time of ST was associated with long-term mortality and major adverse cardiovascular events.

RESULTS

IVUS was performed in 32 of 173 subjects with ST (18%). Stent underexpansion was present in 82% of cases and in all cases of early ST, with a mean stent expansion of 0.7 ± 0.23 by MUSIC criteria. Stent malapposition was most frequently observed in very late ST (40%). In-hospital mortality was similar between subjects who had IVUS performed at the time of ST when compared with the non-IVUS group (3.2% vs. 4.3%, P = 0.8). Subjects who had IVUS performed at the time of ST had lower rates of mortality (HR 0.4, 95% CI 0.1-1.6, P =0.2) and major adverse cardiovascular events (HR 0.5, 95% CI 0.2-1.4, P =0.2) at follow-up, but these values were not statistically significant.

CONCLUSIONS

There is a high prevalence of stent underexpansion in early ST, while the prevalence of malapposition is higher in very late ST. Use of IVUS during treatment for ST may identify mechanisms underlying the development of ST.

Electrocardiographic criteria for ST-elevation myocardial infarction in patients with left ventricular hypertrophy

Patients with electrocardiographic (ECG) left ventricular hypertrophy (LVH) have repolarization abnormalities of the ST segment that may be confused with an ischemic current of injury. We analyzed the ACTIVATE-SF database, a registry of consecutive emergency department ST-segment elevation (STE) myocardial infarction diagnoses from 2 medical centers. Univariate analysis was performed to identify ECG variables associated with presence of an angiographic culprit lesion. Recursive partitioning was then applied to identify a clinical decision-making rule that maximizes sensitivity and specificity for presence of an angiographic culprit lesion. Seventy-nine patients with ECG LVH underwent emergency cardiac catheterization for primary angioplasty. Patients with a culprit lesion had greater magnitude of STE (3.0 ± 1.8 vs 1.9 ± 1.0 mm, p = 0.005), more leads with STE (3.1 ± 1.6 vs 2.0 ± 1.8 leads, p = 0.002), and a greater ratio of STE to R-S-wave magnitude (median 25% vs 9.2%, p = 0.003). Univariate application of ECG criteria had limited sensitivity and a high false-positive rate for identifying patients with an angiographic culprit lesion. In patients with anterior territory STE, using a ratio of ST segment to R-S-wave magnitude ≥25% as a diagnostic criteria for STE myocardial infarction significantly improved specificity for an angiographic culprit lesion without decreasing sensitivity (c-statistic 0.82), with a net reclassification improvement of 37%. In conclusion, application of an ST segment to R-S-wave magnitude ≥25% rule may augment current criteria for determining which patients with ECG LVH should undergo primary angioplasty.

Delaying primary percutaneous coronary intervention for computed tomographic scans in the emergency department

Patients presenting with suspected ST-segment elevation myocardial infarction (STEMI) may have important alternative diagnoses (e.g., aortic dissection, pulmonary emboli) or safety concerns for STEMI management (e.g., head trauma). Computed tomographic (CT) scanning may help in identifying these alternative diagnoses but may also needlessly delay primary percutaneous coronary intervention (PCI). We analyzed the ACTIVATE-SF Registry, which consists of consecutive patients with a clinical diagnosis of STEMI admitted to the emergency departments of 2 urban hospitals. Of 410 patients with a suspected diagnosis of STEMI, 45 (11%) underwent CT scanning before primary PCI. Presenting electrocardiograms, baseline risk factors, and presence of an angiographic culprit vessel were similar in those with and without CT scanning before PCI. Only 2 (4%) of these CT scans changed clinical management by identifying a stroke. Patients who underwent CT scanning had far longer door-to-balloon times (median 166 vs 75 minutes, p <0.001) and higher in-hospital mortality (20% vs 7.8%, p = 0.006). After multivariate adjustment, CT scanning in the emergency department before primary PCI remained independently associated with longer door-to-balloon times (100% longer, 95% confidence interval 60 to 160, p <0.001) but was no longer associated with mortality (odds ratio 1.4, p = 0.5). In conclusion, CT scanning before primary PCI rarely changed management and was associated with significant delays in door-to-balloon times. More judicious use of CT scanning should be considered.

Predictors of depressed left ventricular function in patients presenting with ST-elevation myocardial infarction

Early in the course of ST-segment elevation myocardial infarction (STEMI), therapies that may harm patients who develop left ventricular (LV) dysfunction, such as β-blockers, are often administered. The investigators analyzed the ACTIVATE-SF database, a registry of consecutive STEMI activations presenting to 2 medical centers at the University of California, San Francisco. LV dysfunction was defined as an ejection fraction ≤40% on echocardiography. Of 211 patients included in the analysis, 66 (31%) had LV ejection fractions ≤40%. Patients with LV dysfunction were older (63 ± 15 vs 56 ± 13 years, p = 0.002). In multivariate regression models, decreased renal function (reference group, creatinine <1.0 mg/dl; adjusted odds ratio [AOR] creatinine >1.5 mg/dl 6.35, 95% confidence interval [CI] 1.66 to 24.31, p = 0.007), a history of coronary artery disease (AOR 3.12, 95% CI 1.26 to 7.71, p = 0.014), ST-segment elevation >2 mm on 12-lead electrocardiography (AOR 2.78, 95% CI 1.31 to 5.87, p = 0.008), and need for mechanical ventilation (AOR 3.98, 95% CI 1.41 to 11.19, p = 0.009) increased the odds of LV dysfunction. Inferior ST-segment elevations were associated with 88% decreased odds of LV dysfunction (AOR 0.12, 95% CI 0.06 to 0.35, p <0.001). A prediction score using these characteristics stratified patients into low-, intermediate-, and high-risk groups for LV dysfunction; positive likelihood ratios for LV dysfunction in these groups were 0.07, 1.14, and 4.93, respectively. In conclusion, 5 key predictors of in-hospital LV dysfunction after STEMI were identified; a risk score based on these predictors helps to quickly identify patients presenting with STEMI who are at the highest risk for developing significant LV dysfunction and could guide optimal therapeutic choices.

Multivessel coronary thrombosis treated with abciximab (ReoPro) in a patient with essential thrombocythemia

A 50-year-old man was admitted with acute inferior and anterior myocardial infarction. The patient was diagnosed with essential thrombocythemia (ET) based on the findings of marked thrombocytosis of 1,113 x 10(3)/mm3, splenomegaly, and numerous clumping megakaryocytes on bone marrow biopsy. Emergent coronary angiography revealed extensive multivessel thrombosis involving the left main coronary artery and completely occluding the proximal right coronary artery. In addition to standard therapy with aspirin, heparin, and primary angioplasty of the right coronary artery, the patient received additional antiplatelet therapy with ticlopidine, hydroxyurea, and the platelet glycoprotein IIb/IIIa receptor-inhibiting monoclonal antibody drug abciximab (ReoPro). Serial coronary angiograms 1 and 5 days following the infarction showed progressive thrombus resolution. The pathophysiologic mechanisms and therapeutic challenges of ET-associated coronary thrombosis are discussed in this report.

Clinical features of acute coronary syndromes in patients with human immunodeficiency virus infection

BACKGROUND

Patients with HIV infection exhibit increased rates of coronary events; however, the clinical features of acute coronary syndromes (ACS) in HIV-infected patients have not been well defined.

METHODS AND RESULTS

Between 1993 and 2003, 68 HIV-infected patients were hospitalized with ACS. We compared the clinical features and outcome of these patients with those of 68 randomly selected control patients with ACS without HIV. HIV patients were on average more than a decade younger than controls and more likely to be male and current smokers and to have low HDL cholesterol. They were less likely than controls to have diabetes or hyperlipidemia, and their TIMI (Thrombolysis In Myocardial Infarction) risk scores on admission were significantly lower. At coronary angiography, the number of vessels with >50% stenosis was 1.3+/-1.0 in HIV patients and 1.9+/-1.2 in controls (P=0.007). Restenosis developed in 15 of 29 HIV patients who underwent percutaneous coronary intervention compared with 3 of 21 controls (52% versus 14%, P=0.006).

CONCLUSIONS

HIV patients with ACS are younger and more likely to be males and current smokers and to have low HDL cholesterol levels compared with other ACS patients. Their TIMI risk scores are lower, and they are more likely to have single-vessel disease; however, their restenosis rates after percutaneous coronary intervention are unexpectedly high.

Cyclosporine impairs release of endothelium-derived relaxing factors in epicardial and resistance coronary arteries

BACKGROUND

Cyclosporin A is reported to impair endothelium-mediated vasorelaxation and induce endothelin release in some noncoronary vascular beds. We wished to determine whether acute cyclosporine administration induces endothelial dysfunction in coronary conductance or resistance arteries.

METHODS AND RESULTS

We examined the effect of intracoronary acetylcholine, N omega-nitro-L-arginine methyl ester (L-NAME), L-arginine, nitroglycerin, and adenosine before and after acute cyclosporine administration (3 mg/kg IV over 30 minutes) in anesthetized dogs. Flow velocity was measured with a 0.014-in Doppler wire to assess resistance vessel responses, and epicardial coronary lumen area was simultaneously measured with a 4.3F, 30-MHz imaging catheter inserted over the Doppler wire. In 6 dogs, acetylcholine-induced increase in flow velocity was attenuated by cyclosporine in vehicle (137% to 55% at 10(-5) mol/L, P < .001), as was acetylcholine-induced epicardial vasodilation (14.1% to 6.7% at 10(-5) mol/L, P < .001). Vasodilation in response to intracoronary nitroglycerin (200 micrograms) and adenosine (6 mg) were unchanged by cyclosporine. Epicardial vasoconstriction with L-NAME (10(-4) mol/L) was reduced by cyclosporine (Pre, 7.4 +/- 0.9%; Post, 2.6 +/- 1.2%; P = .04), but L-arginine (10(-4) mol/L) had no effect after cyclosporine. In another 5 dogs, pure cyclosporine impaired acetylcholine-induced vasodilatation to the same degree as cyclosporine in vehicle (Cremophor); vehicle infusion did not impair endothelial function. In 5 more dogs, cyclosporine did not increase either arterial or coronary sinus concentrations of endothelin-1.

CONCLUSIONS

The present study shows that cyclosporine acutely impairs release of endothelium-derived relaxing factor in canine conductance and resistance coronary arteries and provides evidence for decreased epicardial nitric oxide release after cyclosporine. The potential contribution of acute cyclosporine-induced coronary endothelial dysfunction to posttransplant vasculopathy needs further study.

Differential contribution of nitric oxide to regulation of vascular tone in coronary conductance and resistance arteries: intravascular ultrasound studies

We examined the role of nitric oxide in the maintenance of coronary vascular tone in 15 dogs. A 0.014 inch Doppler wire was introduced into the midsegment of the circumflex coronary artery and a 4.3F, 30 MHz two-dimensional ultrasound imaging catheter was introduced over the Doppler wire. Acetylcholine caused a dose-dependent vasodilation in both epicardial and resistance coronary arteries. However, N omega-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide synthetase caused a dose-dependent vasoconstriction mainly in the epicardial coronary arteries, partially reversed by L-arginine. The vasodilator response to acetylcholine was inhibited by L-NAME only in the epicardial circulation. Thus using combined intracoronary two-dimensional and Doppler ultrasound, we have demonstrated both basal and acetylcholine-induced release of nitric oxide in epicardial coronary arteries. The failure of L-NAME to decrease basal and acetylcholine-induced increases in flow velocity suggests that endothelium-dependent relaxation in coronary resistance vessels may not be mediated by nitric oxide alone.

Assessment of coronary conductance and resistance vessel reactivity in response to nitroglycerin, ergonovine and adenosine: in vivo studies with simultaneous intravascular two-dimensional and Doppler ultrasound

OBJECTIVES

The aim of this study was to determine the differential effects of nitroglycerin, ergonovine and adenosine on the resistance vessels in vivo by using a Doppler-tipped guide wire in combination with an ultrasound imaging catheter.

BACKGROUND

Catheter-based two-dimensional intravascular ultrasound yields images of the coronary arteries from which cross-sectional areas can be measured. Intravascular Doppler ultrasound techniques allow measurement of coronary blood flow velocity. The simultaneous use of the two techniques can yield anatomic and physiologic information on conductance and resistance vessels but has not been tried in the coronary arteries.

METHODS

In 15 dogs, we studied coronary flow and vascular reactivity in response to pharmacologic agents using two approaches: 1) a 30-MHz, 4.3F imaging catheter placed alongside a 0.018-in. (0.046 cm) Doppler wire in the circumflex or left anterior descending coronary artery (n = 5); 2) the ultrasound imaging catheter introduced directly over a 0.014-in. (0.036 cm) Doppler wire (n = 10). Vasodilator and vasoconstrictor responses were studied by using intracoronary nitroglycerin (50, 100 and 200 micrograms), ergonovine (200 micrograms) and adenosine (6 mg).

RESULTS

Nitroglycerin caused a dose-dependent increase in epicardial coronary artery cross-sectional area and, to a lesser extent, in average peak flow velocity, resulting in an increase in volumetric coronary blood flow of 39% and 50% at the doses of 100 and 200 micrograms, respectively. With these doses of nitroglycerin, the decrease in diastolic to systolic velocity ratio and the increased change in cross-sectional area from end-diastole to end-systole suggested an enhanced epicardial coronary artery compliance. With ergonovine, a 12% reduction in epicardial coronary artery cross-sectional area was seen, without a significant change in average peak velocity, resulting in a 15% decrease in volumetric coronary blood flow. Adenosine caused a 270% increase in average peak velocity but no change in epicardial coronary artery cross-sectional area, resulting in a 270% increase in volumetric blood flow.

CONCLUSIONS

This study demonstrates that nitroglycerin and ergonovine predominantly influence coronary conductance arteries whereas adenosine mainly dilates coronary resistance vessels. These findings also demonstrate that the combined use of a two-dimensional and a Doppler ultrasound transducer within one catheter assembly can provide information on the differential effects of vasoactive agents on the epicardial and microvascular coronary circulation.

Effect of selective angiotensin II receptor antagonism and angiotensin converting enzyme inhibition on the coronary vasculature in vivo. Intravascular two-dimensional and Doppler ultrasound studies

BACKGROUND

Although angiotensin converting enzyme (ACE) inhibitors have been reported to increase coronary blood flow, the effect of selective angiotensin II (AT1)-receptor antagonism on the coronary circulation has not been defined.

METHODS AND RESULTS

We examined the effects of the AT1-receptor antagonist Losartan (DuP 753, 0.2-3.2 mg/kg) on coronary arteries in vivo in 11 dogs, using a combination of intravascular two-dimensional and Doppler ultrasound. In six dogs, a 30-MHz, 4.3F ultrasound imaging catheter was placed in the midsegment of the circumflex coronary artery to measure cross-sectional area (CSA), and a 0.018-in. Doppler wire was placed alongside to measure coronary flow velocity. At peak effect (1.6 mg/kg), Losartan increased mean coronary CSA from 7.9 +/- 0.5 to 9.5 +/- 0.8 mm2 and average peak velocity (APV) from 32 +/- 10 to 56 +/- 18 cm/sec, resulting in an increase in coronary blood flow from 74 +/- 19 to 151 +/- 36 mL/min. The maximal effect of the ACE inhibitor enalaprilat (5 mg) was an increase in CSA from 7.7 +/- 0.7 to 8.4 +/- 0.8 mm2 and an increase in APV from 36 +/- 10 to 53 +/- 20 cm/sec, with an increase in coronary blood flow from 82 +/- 25 to 122 +/- 41 mL/min. Relative to maximal hyperemia with adenosine (6 mg i.c.), the magnitude of flow increase from baseline was 0.37 with the AT1-receptor antagonist and 0.19 with the ACE inhibitor (p < 0.05). These effects were seen without changes in heart rate or systemic arterial pressure. In an additional five dogs, the ultrasound imaging catheter was introduced directly over a 0.014-in. Doppler wire, and the effects of indomethacin, propranolol, and N omega-nitro-L-arginine methylester (L-NAME) on the vasodilator effect of Losartan (1.6 mg/kg) were examined. Indomethacin and propranolol had no effect on Losartan-induced vasodilation, suggesting that it was not mediated via prostaglandins or beta-adrenoceptors. However, Losartan-induced epicardial vasodilation was partially inhibited by L-NAME, suggesting an action partly dependent on endothelial release of nitric oxide.

CONCLUSIONS

Thus, these acute studies in anesthetized dogs suggest that inhibition of AT1-receptors in the coronary circulation results in vasodilator responses greater in magnitude than ACE inhibition and partly endothelium dependent. The exact role for AT1-receptors in human coronary physiology and pathology remains to be defined.

Pleuritic chest pain in a postpartum woman

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Transvenous coronary ultrasound imaging. A novel approach to visualization of the coronary arteries

BACKGROUND

Catheter-based ultrasound is a new imaging modality to examine endovascular detail in the coronary circulation. This technique requires direct placement of the catheter in the arterial segment of interest.

METHODS AND RESULTS

We examined the feasibility of a less invasive approach by imaging the coronary arterial circulation by using a 5F (30 MHz) imaging catheter placed in the cardiac venous system. Using simultaneous fluoroscopy, we studied anesthetized closed-chest dogs (n = 6) and human subjects undergoing right heart catheterization (n = 11). After cannulation of the coronary sinus, the circumflex coronary artery (Cx) was visualized from the great cardiac vein (GCV), and on advancing the catheter into the anterior interventricular vein (AIV), the left anterior descending artery (LAD) was identified. Where artery and vein were parallel to each other, circular cross-sectional images of the coronary artery were obtained, whereas oblique and transverse orientation of artery to vein produced ellipsoid images or long-axis images. In the dogs, ultrasound-determined cross-sectional area of the coronary arteries (4.81 +/- 0.18 mm2) correlated closely with angiography (4.77 +/- 0.21 mm2) (r = 0.91, p less than 0.001). In humans, the Cx was readily visualized from the GCV in all subjects but because of anatomic variability, the LAD was seen less consistently from the AIV (73%). There was significant correlation between ultrasound-determined cross-sectional areas of the coronary arteries (8.25 +/- 0.34 mm2) with those from angiography (8.59 +/- 0.3 mm2) (r = 0.82, p = 0.001) in humans. In all subjects, the ultrasound transducer could be safely advanced into the AIV to the cardiac apex. Limitations of the technique include ultrasonic penetration problems, caused in part by the large size of human coronary veins and variability in artery-vein relations.

CONCLUSIONS

We conclude that transvenous imaging of coronary arteries with intravascular ultrasound is a less invasive, promising new approach to the study of structure and morphology in the coronary vasculature.

Diagnosis and management of infective endocarditis

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Isolation of cDNA clones for the chicken neural cell adhesion molecule (N-CAM)

Enriched mRNA coding for the neural cell adhesion molecule (N-CAM) was prepared from 9-day embryonic chicken brains by immunoprecipitation of polysomes with antibodies to N-CAM. This mRNA programmed the translation in vitro of N-CAM polypeptide chains in a rabbit reticulocyte lysate system. Two independent N-CAM cDNA clones (designated pEC001 and pEC020) were derived from the enriched RNA. The specificity of pEC001 for N-CAM mRNA was verified by hybrid selection experiments. Both plasmids hybridized to two discrete 6- to 7-kilobase-long RNA species in poly(A)+ RNA from embryonic chicken brain and to lesser amounts of polydisperse material of smaller sizes (probably degradation products of the large RNAs). No hybridization was detected to poly(A)+ RNA from embryonic liver. Southern blotting experiments with pEC001 detected only one hybridizing fragment in chicken genomic DNA digested with several different restriction enzymes, suggesting that sequences corresponding to those within this region of N-CAM mRNA are present at most only a few times, and possibly only once, in the chicken genome.

Dipeptidyl carboxypeptidase from seminal fluid resembles the pulmonary rather than the testicular isoenzyme

The specific activity, molecular weight and immunological behavior of pure dipeptidyl carboxypeptidase from rabbit seminal fluid were found to resemble the corresponding properties of the pulmonary rather than the testicular isozyme.

Tissue-specific expression of mRNAs for dipeptidyl carboxypeptidase isoenzymes

The molecular weight of newly synthesized dipeptidyl carboxypeptidase (angiotensin-converting enzyme; peptidyldipeptide hydrolase, EC 3.4.15.1) polypeptide primed in a reticulocyte lysate by poly(A)-containing RNA from mature rabbit testis was only about 65% that of the immunologically related species programmed by pulmonary RNA. Furthermore, in contrast to the pulmonary RNA-dependent product, the synthesis of this testicular protein was not directed by RNA from testes of immature animals. These findings indicate that a shorter polypeptide chain and pubertal expression--the structural and regulatory properties that distinguish the testicular dipeptidyl carboxypeptidase isozyme--are determined pretranslationally.

Evidence for formation of a rabbit liver aldolase--rabbit liver fructose-1,6-bisphosphatase complex

The ability of rabbit liver aldolase (D-fructose-1,6-bisphosphate D-glyceraldehyde-3-phosphatate-lyase, EC 4.1.2.13) and rabbit liver fructose-1,6-bisphosphatase (Fru-P2ase; D-fructose-1,6-bisphosphate 1-phosphohydrolase, EC 3.1.3.11) to partition into the gel phase of Ultrogel AcA 34 is decreased in a mixture of the two enzymes. Titration experiments indicate that a 1:1 complex is formed. The value for the distribution coefficient of the complex corresponds to a molecular mass of 300,000 daltons, the value expected for a dimer containing one mole of each enzyme protein. Complex formation was not observed when either liver enzyme was replaced by the corresponding isozyme from rabbit muscle. The susceptibility of liver Fru-P2ase to limited proteolysis by subtilisin was reduced in the presence of liver aldolase, but not when the latter was replaced by muscle aldolase, suggesting that the conformation of Fru-P2ase is altered in the complex. Limited proteolysis of liver aldolase abolishes its ability both to form the heterodimer and to protect Fru-P2ase from modification by subtilisin.