The functional activities of myosin head are located in a 95 kilodalton (kDa) heavy chain which can be divided into three fragments of 23 kDa, 50 kDa, and 20 kDa. ATP hydrolysis sites were suggested ...to be located in the 23 kDa and 50 kDa fragments, and actin binding sites were in the 50 kDa and 20 kDa fragments. In this study, we obtained electron microscopic images of the myosin molecule bound with antibodies directed to the 23 kDa and 50 kDa fragments. We determined that the antigenic sites for 23 kDa fragment are located at 140–180 Å from the head-rod junction of myosin, and those for 50 kDa fragment at 160 Å from the junction and at the tip of the head itself. The relationship between the spatial locations and the primary structures is discussed.
Calcium ATPase (Calcium pump) from sarcoplasmic reticulum is an integral membrane protein of M_r 110K and a representative member of P-type ATPase involved in the active transports of ions with the ...energy from ATP hydrolysis. The crystal structure of this enzyme, presumably corresponding the E1 2Ca^2+ state, has been determined at a resolution of 2.6A by using the ultrathin plate crystals of the enzyme and the intense synchrotron X-ray of Spring-8 (Nature 405, 647). The enzyme is composed of 10 transmembrane helices and three well separated soluble domains. Two calcium ions bind to a highly acidic region formed by four transmembrane helices. In particular, the conformation of one helix breaks at the middle having the Pro-Glu-Gly-Leu sequence motif conserved in various P-type ATPases. The break of the helix allows one of the two calcium-binding sites to be formed nearly on the helix. Acidic residues from three transmembrane helices provide another site. The present crystal structure does not fit with a potential map derived from an electron microscopic analysis for this enzyme in the absence of calcium ions, indicating large-scale structural changes between the presence and the absence of ions. The concerted movements of the three soluble domains and the rearrangements of six transmembrane helices are expected during the reaction cycle of the active transport.
Angiotensin receptor blockers (ARBs) plus calcium channel blockers (CCBs) are a widely used combination therapy for hypertensive patients. In order to determine which combination was better as the ...next‐step therapy for standard‐dose combination of ARBs and CCBs, a combination with high‐dose CCBs or a triple combination with diuretics, the authors conducted a prospective, randomized, open‐label trial to determine which of the following combination is better as the next‐step treatment: a combination with high‐dose CCBs or a triple combination with diuretics. Hypertensive outpatients who did not achieve their target blood pressure (BP) with usual dosages of ARBs and amlodipine 5 mg were randomly assigned to treatment with irbesartan 100 mg/amlodipine 10 mg (Group 1: n = 48) or indapamide 1 mg in addition to ARBs plus amlodipine 5 mg (Group 2: n = 46). The primary end point was changes in the systolic BP (SBP) and diastolic BP (DBP) after the 12‐week treatment period, while secondary end points were changes in BP after the 24‐week treatment period and laboratory values. At 12 weeks, the SBP/DBP significantly decreased from 152.1/83.4 mm Hg to 131.5/76.1 mm Hg in Group 1 and 153.9/82.1 mm Hg to 132.7/75.9 mm Hg in Group 2. Although both groups produced a similar efficacy in reducing the SBP/DBP (−19.2/‐9.2 mm Hg in Group 1 and −21.6/‐8.8 mm Hg in Group 2; SBP P = .378, DBP P = .825), high‐dose CCBs combined with ARBs controlled hypertension without elevation of serum uric acid. These results will provide new evidence for selecting optimal combination therapies for uncontrolled hypertensive patients.
A three-dimensional image of the "rigor" complex of actin and chymotryptic myosin subfragment-1 was reconstituted from electron micrographs of negatively stained specimens. Data went out to 20 A ...radially and 26 A axially. The reconstituted images allowed us to deduce the angle between the major axis of the main part of myosin subfragment-1 and the axis of the actin helix. The subfragment-1 molecules were attached to the actin filament in a configuration in which they were tilted by only about 15 degrees from the plane perpendicular to the axis of the actin helix. The implication of the smaller tilt angle than the commonly accepted value is discussed.
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