1. The binding of the competitive inhibitor N-acetyl-d-tryptophan amide to alpha-chymotrypsin has now been studied at pH values up to 10.6, by the technique of equilibrium dialysis. 2. This binding depends on the ionization of a group on the free enzyme with apparent pK(a) 9.3 at 5 degrees . 3. This group is tentatively identified as that responsible for an enzyme conformation change at high pH values, on which the catalytic activity of the enzyme also depends.

Amides↗

PubMed1966

The binding of inhibitors to alpha-chymotrypsin.

1. The binding of three competitive inhibitors, N-acetyl-d-tryptophan, N-acetyl-l-tryptophan and N-acetyl-d-tryptophan amide, to alpha-chymotrypsin was studied over the pH range 2.20-9.65 by the technique of equilibrium dialysis. 2. Within the limits of the experimental method, the binding of the uncharged amide inhibitor is independent of pH over the range investigated. 3. The binding of each of the enantiomeric acids is dependent on the ionization of a group on the free enzyme, of apparent pK(a)7.3. 4. It is shown that the ionizing group results in the active site of the enzyme developing a net negative charge above pH7.3. 5. The enzyme groups responsible are tentatively identified, and the significance of the binding constants with respect to the enzymic catalysis is discussed.

Amides↗

PubMed1929

The lethal effects of ultrasonic radiation.

Explore the source record for details and available documents.

Journal Article↗

PubMedDate not supplied

Biomechanics of the first ray. Part II: Metatarsus primus varus as a cause of hypermobility. A three-dimensional kinematic analysis in a cadaver model.

Variation in functional stability of the first metatarsocuneiform joint was analyzed between transverse plane deviated (adducted) and corrected first metatarsal positions in a closed kinetic chain model. Six fresh frozen cadaver specimens with intact ankles and feet were fitted with a custom fabricated titanium metatarsal jig, which allowed for manipulation of the first metatarsal in the transverse plane. Specimens were mounted into a custom-made acrylic load frame and axially loaded to 400 N. Radiowave three-dimensional tracking transducers were attached to the following osseous segments: first metatarsal head and base, medial cuneiform, and second metatarsal. A dorsally directed load was applied to the first metatarsal segment and resultant movements were measured. Repeated testing was performed on a transverse deviated and corrected first metatarsal positions with the hallux plantargrade and maximally dorsiflexed to engage the windlass mechanism. With the windlass mechanism engaged and first metatarsal corrected, a 26% increase in first ray plantarflexion occurred from a deviated to a corrected first metatarsal position (p < or = .05). This suggests that the windlass mechanism is more efficient when the first metatarsal, sesamoid apparatus, and hallux position are properly aligned with the orientation of the plantar aponeurosis. Clinically, this may explain the correlation of first ray hypermobility with the progression of bunion severity. Our study validates the earlier work of Hicks and adds additional insight into the functional stability in the medial column of the foot.

Acrylic Resins↗

PubMedDate not supplied

Biomechanics of the first ray. Part III. Consequences of Lapidus arthrodesis on peroneus longus function: a three-dimensional kinematic analysis in a cadaver model.

It has long been proposed that first metatarsocuneiform joint (FMCJ) arthrodesis, also known as Lapidus arthrodesis, can realign the first ray and permanently lock the FMCJ to control hypermobility. Left unanswered is the functional consequence of peroneus longus (PL) after such a procedure. In this study, the effects of PL on the medial column of the foot before and after metatarsocuneiform arthrodesis were evaluated. Seven fresh-frozen cadaver specimens with an intact foot and ankle were mounted on a custom-made acrylic frame and loaded to 400 N while midstance motor function was simulated with pneumatic actuators. Three-dimensional radiowave tracking transducers were attached to the first metatarsal, medial cuneiform, navicular, and talus to measure osseous movements while tensile loads of 0% to 100% of PL predicted force was applied. Simulated arthrodesis of the metatarsocuneiform joint and then additionally the intercuneiform 1-2 joint was achieved with titanium pins and then retested to determine any change in effect from PL. Significant frontal plane eversion of the medial cuneiform (p = .016) and dorsiflexion of the talus (p = .045) occurred after Lapidus arthrodesis was achieved. This suggests that arthrodesis at the first metatarsocuneiform joint increases the efficiency of PL stabilizing action on the medial column.

Adult↗

PubMedDate not supplied

Biomechanics of the first ray. Part I. The effects of peroneus longus function: a three-dimensional kinematic study on a cadaver model.

The closed kinetic chain effects of peroneus longus (PL) activity on the medial column of the foot were investigated in seven fresh-frozen cadaver specimens using a three-dimensional radiowave tracking system. Specimens, consisting of the distal half of the leg and the intact ankle and foot, were mounted on a nonmetallic loading frame which allowed positioning of the foot to simulate midstance position of gait. The tibia and fibula were axially loaded to 400 N. Receiving transducers were attached to the first metatarsal, medial cuneiform, navicular, and talus. Tarsal movements were measured as specimens were axially loaded and midstance motor function was simulated using pneumatic actuators. Tensile loads of 0-150% of predicted maximum force were incrementally applied to the PL tendon. Three-dimensional data sets recording osseous positions and orientations were collected and analyzed. Significant frontal plane rotation of the medial column in the direction of eversion occurred when PL strength was increased (p = .0001). Increasing PL loads produced significant but less pronounced angular changes in the sagittal and transverse planes of the medial column. The patterns of motion suggest that PL creates an eversion "locking" effect on the first ray of the foot, stabilizing the medial column.

Biomechanical Phenomena↗

PubMedDate not supplied

Chlorine inactivation of Escherichia coli O157:H7.

We analyzed isolates of Escherichia coli O157:H7 (which has recently caused waterborne outbreaks) and wild-type E. coli to determine their sensitivity to chlorination. Both pathogenic and nonpathogenic strains were significantly reduced within 1 minute of exposure to free chlorine. Results indicate that chlorine levels typically maintained in water systems are sufficient to inactivate these organisms.

Animals↗

PubMedDate not supplied

Live births resulting from unintended pregnancies: is there variation among states? The PRAMS Working Group.

CONTEXT: States need data on live births resulting from unintended pregnancies in order to assess the need for family planning services; however, many states do not collect such data. Some states may use extrapolated rates from other states. METHODS: Pregnancy Risk Assessment Monitoring System (PRAMS) data were assessed to explore the feasibility of extrapolating data on the percentage of live births resulting from unintended pregnancies from states that collect these data to states that do not. Data on women who had live births between 1993 and 1995 were examined for eight states: Alabama, Florida, Georgia, Michigan, New York (excluding New York City), Oklahoma, South Carolina and West Virginia. Logistic regression was used to determine state variation in the odds of delivering a live birth resulting from an unintended pregnancy after adjustment for maternal race, marital status, age, education, previous live birth and participation in the Special Supplemental Nutrition Program for Women, Infants, and Children (WIC). RESULTS: The percentage of live births resulting from unintended pregnancy ranged from 33% in New York to 49% in Alabama, Georgia and South Carolina. Compared with women in Alabama, women in Oklahoma were more likely to deliver a live birth resulting from an unintended pregnancy (odds ratio of 1.2, confidence interval of 1.1-1.3) and women in New York State were less likely (odds ratio of 0.7, confidence interval of 0.6-0.8) to have such a birth. However, unmarried white women in New York had lower odds of having a live birth resulting from an unintended pregnancy and married black women in Michigan had higher odds of having a live birth resulting from unintended pregnancy than their counterparts in Alabama. Although the percentages varied, in all eight states women who were black, were unmarried, were younger than 20 years of age, had less than 12 years of education or had more than one child had higher percentages of live births resulting from unintended pregnancy than women with other demographic characteristics. CONCLUSIONS: Data on which women have the greatest risk of delivering a live birth resulting from an unintended pregnancy may be extrapolated from one state to another, but the rate of such births may overestimate or underestimate the problem from one state to another.

Adolescent↗