The impact of IVUS guided bare metal stent implantation for non-small vessel

Previous studies have shown larger target vessel or greater stent area contribute to reduced restenosis rate. Thus, intravascular ultrasound (IVUS)-guided bare metal stent (BMS) implantation for selected lesions might achieve drug-eluting stent-like outcomes. The aim was to examine the long-term outcomes of BMS using IVUS-guided optimization.

METHODS

Consecutive 103 coronary artery lesions suitable for IVUS were enrolled. Using IVUS, final stent balloon size selected was 90 percent of media-to-media diameter at the lesion or distal reference. The balloon size was listed as follows: group A (3.0-3.5 mm, n = 15), group B (3.5-3.75 mm, n = 64), and group C (3.75-4.5 mm, n = 24).

RESULTS

At post-intervention, average stent area increased by the balloon size (A: 7.2 +/- 1.4 mm2, B: 8.9 +/- 1.5 mm2, and C: 12.1 +/- 2.0 mm2, respectively p < 0.001). At 6 month follow up, the average lumen area increased by balloon size (A: 4.1 +/- 1.7 mm2, B: 5.7 +/- 1.2 mm2, and C: 8.1 +/- 2.0 mm2, respectively p < 0.001). Accordingly, group B and C revealed lower restenosis, compared to group A (A: 46.7%, B: 10.9%, C: 8.3%, A vs B: p = 0.001; C vs A: p = 0.015). Moreover, target lesion revascularization was less in group B and C than group A (A 26.6%, B 3.1%, C 0%, A vs B: p = 0.011; C vs A: p = 0.017).

CONCLUSIONS

For non-small vessels, IVUS-guided BMS implantation showed less restenosis and target lesion revascularization compared to small vessels, mainly due to larger initial gain. These study results suggest that IVUS-guided optimal BMS implantation for selected lesions might result in favorable long-term outcomes similar to those seen using drug-eluting stents. For a decade, coronary stenting has become a standard therapy for coronary artery disease due to favorable long-term outcomes and simple treatment procedure. Furthermore, for the last two years, drug-eluting stents (DES), releasing antiproliferative agents from bare metal backbone, revealed the restenosis rates less than half of those seen using conventional bare metal stents (BMS). While target lesions especially suitable for DES continue to be identified, earlier BMS studies showed that larger target vessel or greater stent area contributed to less restenosis. Thus, optimal IVUS-guided BMS implantation for selected lesions might achieve DES-like long-term outcomes. This study was designed to examine the long-term outcomes of BMS with intravascular ultrasound (IVUS)-guided optimization, using coronary angiography and IVUS data.

Spotty calcification typifies the culprit plaque in patients with acute myocardial infarction: an intravascular ultrasound study

BACKGROUND

Calcification is a common finding in human coronary arteries; however, the relationship between calcification patterns, plaque morphology, and patterns of remodeling of culprit lesions in a comparison of patients with acute coronary syndromes (ACS) and those with stable conditions has not been documented.

METHODS AND RESULTS

Preinterventional intravascular ultrasound (IVUS) images of 178 patients were studied, 61 with acute myocardial infarction (AMI), 70 with unstable angina pectoris (UAP), and 47 with stable angina pectoris (SAP). The frequency of calcium deposits within an arc of less than 90 degrees for all calcium deposits was significantly different in culprit lesions of patients with AMI, UAP, and SAP (P<0.0001). Moreover, the average number of calcium deposits within an arc of <90 degrees per patient was significantly higher in AMI than in SAP (P<0.0005; mean+/-SD, AMI 1.4+/-1.3, SAP 0.5+/-0.8). Conversely, calcium deposits were significantly longer in SAP patients (P<0.0001; mean+/-SD, AMI 2.2+/-1.6, UAP 1.9+/-1.8, and SAP 4.3+/-3.2 mm). In AMI patients, the typical pattern was spotty calcification, associated with a fibrofatty plaque and positive remodeling. In ACS patients showing negative remodeling, no calcification was the most frequent observation. Conversely, SAP patients had the highest frequency of extensive calcification.

CONCLUSIONS

Our observations show that IVUS allows the identification of vulnerable plaques in coronary arteries, not only by identifying a fibrofatty plaque and positive remodeling, but also by identifying a spotty pattern of calcification.

The angiotensin II type 1 receptor blocker valsartan attenuates graft vasculopathy

OBJECTIVE

Transplant arteriosclerosis remains the major cause of graft failure after cardiac transplantation. Here, we investigated the effects of the angiotensin II type 1 receptor blocker valsartan on the development of transplant arteriosclerosis in a murine model of cardiac transplantation.

METHODS

Hearts from DBA/2 (H-2(d)) mice were heterotopically transplanted into B10.D2 (H-2(d)) mice. Recipients were treated with oral administration of valsartan (10 mg/kg/day) or vehicle.

RESULTS

Morphometrical analysis of the cardiac allografts harvested at 30 days revealed that valsartan significantly reduced the development of coronary atherosclerosis (intima/media ratio: 0.39 +/- 0.05 vs. 0.66 +/- 0.08, P < 0.01). At two weeks after transplantation, there was no significant difference between the two groups in expression of adhesion molecules and cytokines. Valsartan significantly reduced the number of peripheral mononuclear cells that differentiated into smooth muscle-like cells in the presence of basic fibroblast growth factor and platelet-derived growth factor BB (18.0 +/- 1.5 vs. 30.3 +/- 4.4 cells/HPF, P = 0.01).

CONCLUSIONS

These results suggest that angiotensin II plays a role in the pathogenesis of transplant arteriosclerosis and that blockade of angiotensin II type 1 receptor might be effective as a prophylactic therapy for transplant arteriosclerosis along with conventional immunosuppressive drugs.

Oolong tea increases plasma adiponectin levels and low-density lipoprotein particle size in patients with coronary artery disease

BACKGROUND

Oolong tea has been studied for its effect on cardiovascular disease and obesity. Plasma adiponectin levels are reduced in obesity, in patients with type 2 diabetes mellitus and in coronary artery disease (CAD).

OBJECTIVE

To investigate prospectively, whether intake of Oolong tea influences plasma adiponectin levels, low-density lipoprotein (LDL) particle size, total cholesterol, high-density lipoprotein (HDL) cholesterol, LDL cholesterol, serum triglyceride and plasma glucose levels in patients with CAD.

METHODS

Twenty two patients in our study consumed Oolong tea (1000 ml) or water for 1 month in our randomized cross-over study design.

RESULTS

There was a significant difference in plasma adiponectin levels before and after 1 month intake of Oolong tea (6.26 +/- 3.26 microg/ml versus 6.88 +/- 3.28 microg/ml, P < 0.05), and in plasma level LDL particle size (25.02+/-0.67 nm versus 25.31+/-0.60 nm, P < 0.01). The water-consuming control group showed no changes (6.28+/-3.28 microg/ml versus 6.23+/-3.21 microg/ml) in adiponectin levels or LDL particle sizes (25.03+/-0.70 nm versus 25.02+/-0.72 nm). We also observed a significant difference in hemoglobin A1c levels (7.23 +/- 4.45% versus 6.99 +/- 4.30%, P < 0.05) before and after intake of Oolong tea.

CONCLUSION

Oolong tea may have beneficial effects on the progression of atherosclerosis in patients with CAD.

Implications of plasma concentrations of adiponectin in patients with coronary artery disease

OBJECTIVE

To investigate whether concentrations of plasma adiponectin constitute a significant coronary risk factor, with particular focus on the relation between plasma concentrations of adiponectin and the development of acute coronary syndrome (ACS).

SUBJECTS AND METHODS

Plasma concentrations of adiponectin were measured in 123 patients with coronary artery disease (CAD) and in 17 control participants. Patients were divided into three groups according to condition type: acute myocardial infarction (AMI) group (n = 59), unstable angina pectoris (UAP) group (n = 28), and stable angina pectoris (SAP) group (n = 36).

RESULTS

Plasma concentrations of adiponectin correlated negatively with body mass index (r = -0.18, p < 0.05), serum triglyceride (r = -0.25, p < 0.01), and fasting glucose concentrations (r = -0.21, p < 0.05), but correlated positively with age (r = 0.26, p < 0.01), high density lipoprotein cholesterol concentrations (r = 0.35, p < 0.01), and low density lipoprotein particle size (r = 0.37, p < 0.01). Plasma concentrations of adiponectin in patients with ACS, in both the AMI and UAP groups, were significantly lower than those in patients with SAP and in the control group (ACS, 6.5 (3.0) microg/ml; SAP, 11.3 (5.9) micro g/ml; control 12.8 (4.3) microg/ml; p < 0.01). Additionally, plasma concentrations of adiponectin in patients with CAD (7.9 (4.6) microg/ml, p < 0.01) were significantly lower than in the control group. There were, however, no significant differences between patients with SAP and the control group (p = 0.36). Multiple logistic regression analysis showed that smoking, fasting glucose concentration, and low log adiponectin concentration correlated independently with the development of an ACS.

CONCLUSIONS

The findings suggest that measurement of plasma concentrations of adiponectin may be of use for assessing the risk of CAD and may be related to the development of ACS.

Circulating monocytes and in-stent neointima after coronary stent implantation

OBJECTIVES

The aim of this study was to investigate the relationship between circulating monocytes and in-stent neointimal volume at six-month follow-up.

BACKGROUND

In-stent neointimal hyperplasia is the main contributing factor to in-stent restenosis. There is increasing evidence that white blood cells (WBCs), especially monocytes, play a central role in restenosis after stent implantation.

METHODS

We performed coronary stent implantation in 107 patients (107 lesions). Peripheral blood was obtained from all patients immediately before coronary angiography and every day for seven days after the intervention, and each WBC fraction count was analyzed. At scheduled six-month follow-up, all patients received angiographic and volumetric intravascular ultrasound analysis.

RESULTS

The circulating monocyte count increased and reached its peak two days after stent implantation (from 350 +/- 167 to 515 +/- 149/mm3, p < 0.01). The maximum monocyte count after stent implantation showed a significant positive correlation with in-stent neointimal volume at six-month follow-up (r = 0.44, p < 0.0001). Other fractions showed neither significant serial changes nor a correlation with in-stent neointimal volume. Multiple regression analysis revealed that in-stent neointimal volume was independently correlated with stent volume immediately after implantation (r = 0.45, p < 0.0001) and maximum monocyte count (r = 0.35, p < 0.001). Angiographic restenosis, defined as percent diameter stenosis >50%, was observed in 22 patients (21%), and these patients showed a significantly larger maximum monocyte count than patients without restenosis (642 +/- 110 vs. 529 +/- 77/mm3, p < 0.01).

CONCLUSIONS

Circulating monocytes increased after coronary stent implantation, and the peak monocyte count related to in-stent neointimal volume. Our results suggest that circulating monocytes play a role in the process of in-stent neointimal hyperplasia.

Circadian variation of plaque rupture in acute myocardial infarction

Studies have reported a circadian variation in the onset of acute myocardial infarction (AMI). Pathologic studies have revealed that plaque rupture is 1 of the major causes of AMI, but none of these has looked specifically at the circadian variation of plaque rupture. The aim of this study was to use intravascular ultrasound (IVUS) to investigate the circadian variation of plaque rupture in AMI. This study included 174 consecutive patients with AMI who underwent preinterventional IVUS. All patients were assigned to either a rupture group or a nonrupture group according to the preinterventional IVUS. In the 81 patients (47%) in the rupture group, the frequency of the onset of AMI increased significantly in the period from 6 A.M. to 12 P.M. compared with all other time periods (p <0.05). The clinical features of AMI in the rupture group were characterized as occurring significantly more at rest (67% vs 31%, p <0.01) and after significantly less preinfarction angina (22% vs 57%, p <0.01) compared with the nonrupture group. A different circadian variation was identified in the nonrupture group, characterized as a significant nocturnal nadir (12 to 6 A.M. compared with all other periods, p <0.05). The circadian variation of AMI is the result of a morning increase in incidence of plaque rupture.

Long-Term Beneficial Effect of Infarct-Related Artery Patency in Acute Anterior Myocardial Infarction in Patients With Poor Myocardial Viability in the Region-at-Risk

BACKGROUND

Several studies have demonstrated the benefit of the patency of infarct-related artery (IRA) in acute myocardial infarction (AMI). However those studies have not been concerned with myocardial viability in the region-at-risk. In the present study the effect of the patency of IRA was investigated in the setting of anterior AMI with poor viable myocardium in the risk region.

METHODS AND RESULTS

From 1993 to 1996 patients with a first time anterior AMI and poor viable myocardium in the region-at-risk at 1 month after onset were identified and enrolled. Patients with a totally occluded IRA were included in the Non-Open group (n=44), and patients with a reperfused IRA were included in the Open group (n=49). At 5 years after onset, left ventricular function was better preserved in the Open group than in the Non-Open group (p<0.05). Kaplan-Meier survival curves for cardiac mortality and event-free survival curves revealed poor prognoses in the Non-Open group over a 5-year period (p<0.05, respectively). The advantages of a patent IRA were further seen in health-related quality-of-life outcomes (p<0.05).

CONCLUSIONS

Even in patients with poor myocardial viability after an anterior AMI, the patency of the IRA is strongly associated with improved long-term survival, independent of residual myocardium viability.

In-stent restenosis and lesion morphology in patients with acute myocardial infarction

We investigated the correlation between lesion morphology with preintervention intravascular ultrasound and in-stent restenosis in 72 patients with acute myocardial infarction (AMI). Multivariate logistic regression analysis showed that the presence of ruptured plaque was the only predictive factor of in-stent restenosis after primary stenting for AMI.

C-reactive protein and lesion morphology in patients with acute myocardial infarction

BACKGROUND

Elevated serum C-reactive protein (CRP) is of clinical significance in the management of acute coronary syndromes, but there have been few in vivo studies detailing the relation between lesion morphology and elevated CRP in the setting of acute myocardial infarction (AMI). In this study, we investigated the relation between lesion morphology as seen under preintervention intravascular ultrasound (IVUS) and CRP in the acute phase of AMI.

METHODS AND RESULTS

Our patient population comprised 90 consecutive patients with AMI who underwent preintervention IVUS within 6 hours of the onset of symptoms. Patients were divided into an elevated CRP group (> or =3 mg/L) or a normal CRP group on the basis of serum CRP levels. There were no differences in patient characteristics or angiographic findings. We observed significantly more plaque rupture in the elevated CRP group than in the normal CRP group (70% versus 43%, P=0.01). A multivariate logistic regression model revealed that the presence of ruptured plaque alone correlated with elevation of serum CRP (P=0.02; odds ratio, 3.35; 95% CI, 1.22 to 9.18).

CONCLUSIONS

Elevated CRP may be related to the presence of ruptured plaque. Our results suggest that in the setting of AMI, elevated CRP levels may reflect the inflammatory activity of a ruptured plaque.

Predicting angiographic distal embolization following percutaneous coronary intervention in patients with acute myocardial infarction

The aim of this study was to investigate the relation between lesion morphology identified by intravascular ultrasound (IVUS) before intervention and angiographic distal embolization after percutaneous coronary intervention (PCI) in patients with acute myocardial infarction (AMI). PCI for AMI has already been established as beneficial therapy, although some complications remain unresolved. Distal embolization is 1 of the important complications of PCI. Recently, some new devices have been developed for the prevention of distal embolization. However, few studies exist that look into the relation between lesion morphology and distal embolization. IVUS was performed safely in 140 consecutive patients with AMI before coronary intervention. No patient received thrombolytic therapy. From the incidence of angiographic distal embolization, patients were divided into 2 groups--an embolization group and a nonembolization group--and clinical background, IVUS, and angiographic information were evaluated. Distal embolization was observed in 12 patients (9%). Peak creatine kinase levels (3,877 +/- 2,285 vs 2,293 +/- 1,792 IU/L, p <0.05) and the incidence of angiographic thrombus (25% vs 5%, p <0.05) and intracoronary mobile mass detected by IVUS (75% vs 16%, p <0.001) were higher for patients in the embolization group. From the multivariate logistic regression analysis, only an intracoronary mobile mass detected by IVUS emerged as a predictor of distal embolization (odds ratio 53, 95% confidence interval 2.7 to 1,040, p <0.01). Patients with an intracoronary mobile mass detected by IVUS are prone to distal embolization after PCI and larger infarction. IVUS imaging before PCI may be useful for determining which patients need a distal protection device.

Assessment of myocardial viability using coronary zero flow pressure after successful angioplasty in patients with acute anterior myocardial infarction

OBJECTIVES

To investigate the relation between coronary flow reserve (CFR), coronary zero flow pressure (Pzf), and residual myocardial viability in patients with acute myocardial infarction.

DESIGNS

Prospective study.

SETTING

Primary care hospital.

PATIENTS

27 consecutive patients with acute anterior myocardial infarction.

MAIN OUTCOME MEASURES

F-fluorodeoxyglucose (FDG) positron emission tomography (PET) was used in 27 patients who underwent successful intervention within 12 hours of onset of a first acute anterior myocardial infarction. Within three days before discharge they had < 25% stenosis in the culprit lesion as determined by angiography 24 (3) days after acute myocardial infarction. Pzf and the slope index of the flow-pressure relation (SIFP) were calculated from the simultaneously recorded aortic pressure and coronary flow velocity signals at peak hyperaemia.%FDG was quantified by comparing FDG uptake in the infarct myocardium with FDG uptake in the normal myocardium.

RESULTS

There was a correlation between %FDG and CFR, where y = -1.477x + 62.517, r = -0.072 (NS). There was also a correlation between %FDG and SIFP, where y = -0.975x + 60.542, r = -0.045 (NS), and a significant correlation between %FDG and Pzf, where y = -0.98x + 85.108, r = -0.696 (p < 0.001).

CONCLUSIONS

CFR does not correlate with FDG-PET at the time of postreperfusion evaluation of residual myocardial viability. The parameter that correlates best with residual myocardial viability is Pzf and this may be a useful index for predicting patient prognosis.

No-reflow phenomenon and lesion morphology in patients with acute myocardial infarction

BACKGROUND

The no-reflow phenomenon is associated with poor functional and clinical outcomes for patients with acute myocardial infarction (AMI). In the era of primary intervention, accurately identifying lesions at high risk of no reflow is of crucial importance. At present, no study into the relationship between lesion morphology and no reflow has been performed. The aim of this study was to investigate the relationship between preintervention intravascular ultrasound (IVUS) lesion morphology and the no-reflow phenomenon.

METHODS AND RESULTS

This study comprised 100 consecutive patients with AMI who underwent preintervention IVUS and were successfully recanalized with primary balloon angioplasty or stenting. IVUS was again performed to identify and exclude any mechanical vessel obstruction in cases of thrombolysis in myocardial infarction flow grade 0, 1, or 2 after intervention in the absence of angiographic stenosis. Angiographic no reflow was seen in 13 patients (13%). Univariate analysis indicated that hypercholesterolemia, fissure and dissection, lipid pool-like image, lesion, and reference external elastic membrane cross-sectional area correlate with the no-reflow phenomenon. Multivariate logistic regression analysis showed that lipid pool-like image (P<0.05; odds ratio 118; 95% CI, 1.28 to 11 008) and lesion elastic membrane cross-sectional area (P<0.05; odds ratio 1.55; 95% CI 1.01 to 2.38) are independent predictive factors of no-reflow phenomenon after reperfusion for AMI.

CONCLUSIONS

Large vessels with lipid pool-like image are at high risk for no reflow after primary intervention for AMI. Also, plaque content may play a role in damage to the microcirculation after primary intervention for AMI.

Content validity of a Scale to measure silencing and affectivity among women living with HIV/AIDS

This study measured quantitatively and explored qualitatively silencing behaviors and affectivity (mood) in women living with HIV/AIDS and confirmed the validity of the Silencing the Self Scale and the Positive and Negative Affect Scale. Silencing behaviors are interpersonal communication styles that suppress personal needs and feelings to preserve relationships with others. Silencing behaviors serve as protective strategies that allow one to divorce oneself from an overbearing culture. Affectivity is a way of measuring one's personal mood state by a positive to negative continuum. The results indicate that the women silenced themselves profoundly, especially when it came to putting the needs of their children or dependents before their own. The women also had high levels of negative affectivity. The research findings from this study extend nursing knowledge by addressing the unique social processes of women living with HIV/AIDS within health care service structures and significant social groups. Further exploration of "silencing" as a phenomenon of this group through measurement and experience will help define specific interventions that are meaningful to and for women living with HIV/AIDS.

Lesion characteristics of acute myocardial infarction: an investigation with intravascular ultrasound

OBJECTIVE

To use intravascular ultrasound (IVUS) to compare plaque morphology in acute myocardial infarction and stable angina pectoris.

DESIGN

Retrospective study.

SETTING

Primary care hospital.

PATIENTS

59 consecutive cases of acute myocardial infarction and 50 consecutive cases of stable angina pectoris.

METHODS

IVUS was used before coronary intervention.

MAIN OUTCOME MEASURES

Plaque morphology (incidence of eccentric plaque, subtle dissections, low echoic thrombus, calcification, echolucent areas, and bright speckled echo material), assessed visually using IVUS.

RESULTS

There were no significant differences in plaque eccentricity or calcification between the two groups, but low echoic thrombus (acute myocardial infarction 15% v stable angina pectoris 0%), subtle dissections (37% v 4%), echolucent areas (31% v 0%), and bright speckled echo material (90% v 0%) were more common in the infarction group than in the stable angina group (p < 0.001 for all). There was a longer time between the onset of symptoms and the IVUS examination in patients with low echoic thrombus than in those without (p < 0.03).

CONCLUSIONS

Low echoic thrombus, subtle dissections, echolucent areas, and bright speckled echo material are morphological characteristics associated with plaque at the time of acute myocardial infarction. These findings correspond pathologically to ruptured plaque.

[A retroperitoneal leiomyosarcoma--a case of non-concurrent double cancers with kidney cancer]

A retroperitoneal leiomyosarcoma in a 50-year-old man is reported. A laparotomy was performed on Dec. 17, 1987 and the tumor, weighing 120 g, was completely excised. The patient was followed up and has stayed healthy (1 year after operation). Although CT ultrasonography and arteriography are helpful in the diagnosis of retroperitoneal tumors, it is felt that a histological examination is indispensable for a qualitative assessment of the lesion. Surgical excision constitutes the fundamental treatment for a retroperitoneal leiomyosarcoma. However, the prognosis is usually poor and depends on successful radical surgery. This case involved non-concurrent double cancers with a retroperitoneal leiomyosarcoma and a kidney cancer.

[Case report of a second resection of rectal leiomyosarcoma due to recurrence after 10 years]

A leiomyosarcoma of the rectum is a rare disease, and cases of a recurrence are even more rare. Reported is the case of a patient who, in 1987, underwent a per sacral resection of a rectal tumor which was diagnosed as leiomyosarcoma. In 1987, after symptoms that showed that the patient's feces had become narrower, a recurrence of this tumor was diagnosed, so that the patient again underwent an abdominoperineal rectomy. The postoperative course has been good. Details of this disease still remain unclear. In Japan, there have been only 10 such cases of a recurrence reported. Of these, a liver metastasis and a localized recurrence are the most common. Long term follow-ups are considered necessary.

Microbiological transformations of delta6a10a-tetrahydrocannabinol

A screening program was conducted to find microorganisms that catalyze transformation reactions with cannabinoids. Three hundred fifty-eight cultures, consisting of 97 bacteria, 175 actinomycetes, and 86 molds, were incubated in media containing 0.5 mg of Delta(6a,10a)-tetrahydrocannabinol (Delta(6a,10a)-THC) per ml. After 120 h of cultivation, ethyl acetate extracts of the cultures were examined by thin-layer chromatography (TLC) for transformation products. About 18% of the cultures modified Delta(6a,10a)-THC. The ability to modify the substrate did not predominate among any particular group of microorganisms. After purification, the products from three cultures were analyzed by high-resolution mass spectrometry, 100-mHz proton magnetic resonance spectrometry, ultraviolet spectrometry, and infrared spectrometry. These spectral data indicated that a Mycobacterium sp. oxidized Delta(6a,10a)-THC to cannabinol and a diastereomeric pair of 6a-hydroxy-Delta(10,10a)-THC isomers; a Streptomyces sp. and a Bacillus sp. oxidized Delta(6a,10a)-THC to 7-keto-Delta(6a,10a)-THC and 4'-hydroxy-Delta(6a,10a)-THC, respectively. The occurrence of these products and the presence of others that have not yet been isolated or identified indicate that microbial transformation may be a useful tool for the preparation of new cannabinoids that have desirable pharmacological properties.

Physical properties and kinetic behavior of a cephalosporin acetylesterase produced by Bacillus subtilis

An esterase that deacetylates cephalosporins was recovered from the supernatant of a Bacillus subtilis culture. It was partially purified by ammonium sulfate fractionation and ultrafiltration. The enzyme had a temperature optimum between 40 and 50 C and a pH optimum of 7.0. The molecular weight was estimated by gel filtration to be 190,000. The enzyme was very stable and retained greater than 80% of its activity after storage in solution at 25 C for 1 month. The esterase exhibited Michaelis-Menton kinetics with the substrates 7-aminocephalosporanic acid (7-ACA) and 7-(thiophene-2-acetamido)cephalosporanic acid (cephalothin); the K(m) values were 2.8 X 10(-3) and 8.3 X 10(-3) M, respectively. The products of 7-ACA deacetylation were weak competitive inhibitors, and a K(i) value of 5.0 X 10(-2) M was determined for acetate and of 3.6 X 10-2 M for deacetyl-7-ACA. Weak product inhibition did not prevent the deacetylation reaction from going to completion. A 5-mg/ml solution of partially purified esterase completely hydrolyzed (greater than 99.5%) a 24-mg/ml solution of 7-ACA in 3 h. Because of the kinetic properties and excellent stability, this enzyme may be useful in an immobilized form to prepare large quantities of deacetylated cephalosporin derivatives.