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The greater trochanter is palpated discount malegra dxt plus 160mg otc, and the soft-tissue attachments of the gluteus medius 1 cm proximal to the bony tip of the greater trochanter are incised using electrocautery buy generic malegra dxt plus 160mg line. These soft-tissue attach- ments extend posteriorly along the posterior border of the femur (Fig- ure S3 buy 160mg malegra dxt plus with mastercard. The anterior third of the gluteus medius on the anterior aspect of the greater trochanter usually can be left in place because it typically is not contracted in external rotation abduction contractures buy malegra dxt plus 160 mg with amex. The re- lease must be almost completely along the posterior aspect cheap malegra dxt plus 160 mg otc. Going posterior is very important, especially to identify and transect the piriformis tendon and going further inferior to transect the gemelli (Figure S3. Next, if more release is needed, the hip joint capsule is exposed, and if the capsule is very tight limiting internal rotation, an incision in the posterior capsule midway between the acetabulum and the femur can be performed safely (Figure S3. Bleeding points are cauterized, and only the subcutaneous tissue and skin should be closed. This same procedure can be modified for an internal rotation con- tracture, but the incision should be curved slightly anteriorly. In this circumstance, only the anterior third to anterior half of the abductor is removed. If this procedure is being performed in a child who is non- ambulatory, the whole muscle mass is removed to decrease the amount of internal rotator force (Figure S3. In an ambulatory child, the anterior part of the muscle is incised; then, with careful retraction, the fascia underlying the abductor is identi- fied and only the fascia is incised to effect a myofascial lengthening of the anterior half of the abductor muscle (Figure S3. Postoperative Care Immediate active and passive range of motion is started on the first postop- erative day. Parents are instructed to try to keep the child’s hips adducted, or if the release was for internal rotation, to keep the hips externally rotated during sleep at night. This should be accomplished with positioning, not with rigid braces. Resection Arthroplasty Indication This procedure is indicated as a palliative treatment to decrease the hip pain in nonambulatory children and adults with painful dislocated hips in which there is severe degenerative arthritis and deformity of the femoral head and ac- etabulum. It is the primary procedure in cases where there is skin breakdown. The incision is made over the lateral border of the femur carried down the subcutaneous tissue. The incision should extend distally from the tip of the palpable greater trochanter to approximately 6 or 8 cm (Figure S3. The fascia latae is incised longitudinally and then the vastus lateralis is identified. The fascia of the vastus lateralis is opened longitudinally; however, subperiosteal dissection of the femur should not be obtained. Using fluoroscopic control, the interval between the muscle and perio- steum is identified at the inferior aspect of the ischium. Using an oscillating saw, the femur is transected at this level (Figure S3. After the femur has been transected, the proximal femur is resected using electrocautery to avoid any subperiosteal dissection because leaving the periosteum tends to cause heterotopic ossification. All of the periosteum and proximal femur are resected with a slight sleeve of soft tissue with extensive use of electrocautery to help minimize bleeding. The hip joint capsule usually is resected right at the border of the femoral neck, leaving a sleeve of hip joint capsule associated with the residual acetabulum. The abductor muscle also is resected well off the tip of the greater trochanter so that no apophysis that might form bone is remaining. After the proximal fragment is removed, sutures are placed in an at- tempt to cover the rough and open bone on the ilium by suturing hip joint capsule and muscle over this area (Figure S3. The sleeve of vastus lateralis, which had been freed off the proximal fragment, is sutured over the top of the exposed bone on the distal fragment (Figure S3. The vastus lateralis then is closed tightly, subcutaneous tissue and skin are closed, and the child is placed in skeletal traction or a well leg cast with broomsticks between the legs to provide some traction and positioning.
The active site is usually a cleft or crevice in the or enzyme formed by one or more regions of the polypeptide chain malegra dxt plus 160mg free shipping. Within the active ATP: D–glucose– 6–phosphotransferase ADP site order 160 mg malegra dxt plus with visa, cofactors and functional groups from the polypeptide chain participate in trans- forming the bound substrate molecules into products purchase 160mg malegra dxt plus amex. CH2O P Initially buy generic malegra dxt plus 160mg line, the substrate molecules bind to their substrate binding sites best 160 mg malegra dxt plus, also called O the substrate recognition sites (see Fig. The three-dimensional arrangement H of binding sites in a crevice of the enzyme allows the reacting portions of the sub- strates to approach each other from the appropriate angles. The proximity of the HO OH H OH bound substrate molecules and their precise orientation toward each other con- H OH tribute to the catalytic power of the enzyme. The active site also contains functional groups that directly participate in the Fig. Reaction catalyzed by glucokinase, reaction (see Fig. The functional groups are donated by the polypeptide an example of enzyme reaction specificity. As the substrate binds, it induces conformational changes in the enzyme phate from ATP to carbon 6 of glucose. It can- not rapidly transfer a phosphate from other that promote further interactions between the substrate molecules and the nucleotides to glucose, or from ATP to closely enzyme functional groups. Additional bonds with the enzyme stabilize the transition state complex and decrease the energy required for its formation. A Substrate C Enzyme Additional Active site bonds Cofactors Free enzyme Transition state complex B D Substrate binding site Products Enzyme–substrate complex Original enzyme Fig. The enzyme contains an active cat- alytic site, shown in dark blue, with a region or domain where the substrate binds. The active site also may contain cofactors, nonprotein components that assist in catalysis. The sub- strate forms bonds with amino acid residues in the substrate binding site, shown in light blue. Substrate binding induces a conformational change in the active site. Functional groups of amino acid residues and cofactors in the active site participate in forming the tran- sition state complex, which is stabilized by additional noncovalent bonds with the enzyme, shown in blue. As the products of the reaction dissociate, the enzyme returns to its original conformation. The free enzyme then binds another set of substrates, and repeats the process. Substrate Binding Sites Enzyme specificity (the enzyme’s ability to react with just one substrate) results from the three-dimensional arrangement of specific amino acid residues in the enzyme that form binding sites for the substrates and activate the substrates during the course of the reaction. The “lock-and-key” and the “induced-fit” models for substrate binding describe two aspects of the binding interaction between the enzyme and substrate. LOCK-AND-KEY MODEL FOR SUBSTRATE BINDING The substrate binding site contains amino acid residues arranged in a complemen- tary three-dimensional surface that “recognizes” the substrate and binds it through multiple hydrophobic interactions, electrostatic interactions, or hydrogen bonds (Fig. The amino acid residues that bind the substrate can come from very dif- ferent parts of the linear amino acid sequence of the enzyme, as seen in glucokinase. The binding of compounds with a structure that differs from the substrate even to a small degree may be prevented by steric hindrance and charge-repulsion. In the lock-and-key model, the complementarity between the substrate and its binding site is compared to that of a key fitting into a rigid lock. As the substrate binds, enzymes undergo a conformational change (“induced fit”) that repositions the side chains of the amino acids in the active site and increases the number of binding interactions (see Fig. The induced fit model for substrate bind- A Asp–205 HN Gly–229 O B OH O O OH HO O O Asn–204 HO HO Glucose OH Galactose OH OH NH2 HO HO O O NH2 O O Glu– 290 Asn–231 O Glu–256 Fig. Glucose, shown in blue, is held in its binding site by multiple hydrogen bonds between each hydroxyl group and polar amino acids from different regions of the enzyme amino acid sequence in the actin fold (see Chapter 7). The position of the amino acid residue in the linear sequence is given by its number. The multiple interactions enable glucose to induce large conformational changes in the enzyme. Glucokinase : structaral analysis of a protein involved in susceptibility to diabetes 1994;21925–21928.
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