Statistical evidence for two major proteins in freeze‐fractured gastric parietal cell tubulovesicles and canaliculus

Abstract

In a previous work, resting and acid-secreting rabbit gastric mucosa were freeze-fractured and shadowed at 45 degrees with Pt-C. The shadow widths of proteic particles of tubulovesicle and canaliculus membranes were measured and compared. It was concluded that the frequency distributions of widths are significantly different in resting and secreting membranes and that each distribution accounts for several subpopulations of homogeneous particles. In the present study, an attempt is made to describe the experimental distributions as a mixture of those of two major proteins, say A and B and their aggregates (AA, AB and BB). The modelling, although simple, gave a very satisfactory statistical fit between observed and computed distributions. The comparison of parameters calculated from histamine and ranitidine experimental data further improves the fits and finally, component A accounts for 69% of the particles. Most replica of A particles are heart-shaped and the median shadow widths are 6.1 and 6.8 nm in canaliculus and tubulovesicles respectively. The component B accounts for 31% of the particles. They mainly appear as small barrels and the median shadow widths are 8.8 and 10.3 nm in canaliculus and tubulovesicles respectively. According to calculated parameters and observed particle replica, the onset of secretion does not change the relative ratio of proteins but changes their shapes. Component A should be the (H+,K+)-ATPase whereas debate on the identity of B is wide open.

Structural and Functional Study of Reconstituted Peripheral Benzodiazepine Receptor

“…The population of diameters was a mixture of log normal populations. The parameters of the mixture (i.e., proportions, mean and standard deviation of each component) were estimated by maximum likelihood (22). The concordance of empirical and estimated distributions was assessed by examination of the PP-plot (23).…”

In Vivo and in Vitro Peripheral-Type Benzodiazepine Receptor Polymerization: Functional Significance in Drug Ligand and Cholesterol Binding

“…Since these measurements were made directly from the platinum/carbon layers, it was necessary to establish the corrected value of the intravesicular particles alone. The latter value was calculated as the directly measured value minus the thickness of the deposited replica (3,46,47). Consequently, the corrected average sizes for the three populations were derived as 3.5, 7.0, and 14 nm, respectively, suggesting the presence of monomers, dimers, and tetramers.…”