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Biomedical subjects

P Whitley

Publications and source records attributed to P Whitley.

43 records · Page 3Linked to original sources
PubMed1994

The COOH-terminal ends of internal signal and signal-anchor sequences are positioned differently in the ER translocase.

Signal peptides (SPs) target proteins to the secretory pathway and are cleaved from the nascent chain once the translocase in the ER has been engaged. Signal-anchor (SA) sequences also interact transiently with the ER translocase, but are not cleaved and move laterally out of the translocase to become permanent membrane anchors. One obvious difference between SP and SA sequences is the considerably longer hydrophobic regions (h regions) of the latter. To study the interaction between SP/SA sequences and the ER translocase, we have constructed signal sequences with poly-Leu h regions ranging in length from 8 to 29 residues and have characterized their locations within the translocase using both a new assay that measures the minimum number of amino acids needed to span the distance between the COOH-terminal end of the h region and the active site of the oligosaccharyl transferase enzyme and an assay where the efficiency of signal peptidase catalyzed cleavage is measured. Our results suggest that SP and SA sequences are positioned differently in the ER translocase.

Amino Acid Sequence↗
PubMed1993

The DsbA-DsbB system affects the formation of disulfide bonds in periplasmic but not in intramembraneous protein domains.

The DsbA and DsbB proteins of Escherichia coli are involved in facilitating the formation of disulfide bonds in periplasmic proteins. Here, we show that the rate of formation of a disulfide bond in the periplasmic domain of the inner membrane protein leader peptidase is reduced in dsbA and dsbB strains, whereas the rate of formation of a disulfide bond engineered into the membrane embedded domain of the same protein is completely unaffected by these mutations. We conclude that the Dsb proteins do not facilitate the formation of intramembraneous disulfides.

Bacterial Proteins↗
PubMed1993

Three-dimensional model for the membrane domain of Escherichia coli leader peptidase based on disulfide mapping.

We have mapped the interface between the two transmembrane alpha-helices in the membrane domain of the Escherichia coli enzyme leader peptidase by analyzing disulfides formed between pairs of cysteine residues introduced near their respective periplasmic ends. The interface is formed primarily from aliphatic amino acids, and the two helices appear to pack against each other in a left-handed supercoil. We suggest that disulfide mapping may be a generally applicable approach for the construction of models of helix-helix interfaces in membrane proteins.

Amino Acid Sequence↗
PubMed1990

Platelet storage lesions in second-generation containers: correlation with in vivo behavior with storage up to 14 days.

The relationship between in vivo behavior and in vitro characteristics of 59 platelet concentrates (PC) stored for up to 14 days in a synthetic medium or in CPDA-1 plasma was systematically investigated. 25 paired studies (1 study was incomplete) were performed comparing platelets suspended either in the synthetic medium or CPDA-1 plasma with 5 days (n = 5); 7 days (n = 10); 10 days (n = 5); and 14 days (n = 5) of storage. In addition, 10 control studies were performed with freshly prepared PC (6-24 h) in CPDA-1 plasma. Both percent recovery and survival estimations showed decreases with increasing storage duration, irrespective of storage medium used. In both media, with prolonged storage, the platelet survival curves not only became shorter, but also increasingly exponential, suggesting that in vitro storage caused progressive damage to the platelets present in circulation. Survival curves of platelets suspended in synthetic medium remained more linear, indicative of less random damage during storage. Mean population lifespan (MPL) of the stored PC was determined by the area below the survival curve divided by the mean percent recovery for the fresh PC, which was 55%. MPL decreased from 4.5 days (fresh PC) to 0.4 days after 14 days of storage in plasma, with a 50% reduction (t1/2) estimated at 7.2 days of storage. MPL t1/2 for PC stored in the synthetic medium was estimated to be 8.8 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Properties of platelet concentrates prepared after extended whole blood holding time.

Extension of the maximum holding time for whole blood collected into a CPD-ADSOL system from 6 to 8 hours at ambient temperature under conditions that cause the temperature of the blood to decrease to 20 to 24 degrees C would facilitate the preparation of platelet concentrates (PCs). In this study, the properties of CPD-PCs prepared and stored for 5 days in PL-732 containers after various initial holding periods were assessed in two laboratories, designated Laboratory A and Laboratory B. Laboratory A found higher platelet-rich plasma (PRP) volumes (276 +/- 25 vs. 249 +/- 19 mL) and platelet yields (76 +/- 18 vs. 66 +/- 18 x 10(9) platelets) with 8-hour holds (n = 10) than with 1- to 2-hour holds (n = 10), although only the difference in PRP volumes was significant (p less than 0.05). No significant difference was observed in autologous in vivo recovery (54 +/- 11 vs. 47 +/- 9%) or survival (167 +/- 37 vs. 170 +/- 25 hrs), as calculated by gamma function using 111In as radiolabel. Laboratory B also found higher PRP volumes (304 +/- 31 vs. 279 +/- 37 mL) and platelet yields with 8-hour holds (n = 12) than with a 6-hour holds (n = 10) (88 +/- 26 vs. 77 +/- 27 x 10(9) platelets). No significant differences were found in morphology score, the extent of release of beta-thromboglobulin, the discharge of lactate dehydrogenase, or hypotonic shock response.(ABSTRACT TRUNCATED AT 250 WORDS)

Adenosine Triphosphate↗
PubMedDate not supplied

A quantitative assay to determine the amount of signal peptidase I in E. coli and the orientation of membrane vesicles.

The number of Signal Peptidase I (SPasel) molecules per E. coli cell was determined using western blot techniques. Different strains were found to contain approximately 1000 SPasel molecules per cell during exponential growth. Based on the activity of SPasel in vitro it could be estimated that this amount is sufficient to process all translocated precursors. SPasel did not appear to be under growth phase dependent control, but was constitutively expressed. The quantitative western blot technique was also used to establish the orientation and intactness of isolated inner membrane vesicles.

Bacterial Proteins↗