A novel view of albumin-supported sperm capacitation: role of lipid transfer protein-I.
OBJECTIVE
To determine if one mechanism of albumin-mediated support of human sperm capacitation is lipid (cholesterol) transfer activity and contamination of albumin with Lipid Transfer Protein-I (LTP-I).


METHODS
Measure lipid transfer activity in various bovine and human albumin preparations, relate this activity to albumin-supported capacitation (measured by zona-free hamster oocyte sperm penetration assay) and acrosome reactions; and attempt to detect LTP-I in active albumins. Remove LTP-I from albumin which supports capacitation and reassess this support. Reconstitute capacitation support by addition of purified LTP-I.


METHODS
Healthy sperm donors with normal semen analyses were recruited by the Reproductive Biology-Andrology Laboratory in a university medical center.


RESULTS
Albumin preparations that effectively support capacitation have high levels of lipid transfer activity and of LTP-I, a protein responsible for lipid transfer activity. Preparations with lower levels of capacitation support have less lipid transfer activity. Removal of LTP-I from supportive albumin significantly reduces the capacitation support, and this is restored by purified LTP-I. Progesterone concentrations in these preparations are negligible.


CONCLUSIONS
The variable abilities of albumin preparations to support in vitro sperm capacitation are largely dependent on the presence of contaminating LTP-I. The cholesterol transfer activity of this protein, which is present in human serum and follicular fluid, may be one mechanism in the process of capacitation.
Ravnik
S E
SE
Department of Obstetrics and Gynecology, University of Washington, Seattle 98195.
Albers
J J
JJ
Muller
C H
CH
D000177:Acrosome / Q000502:physiology; D000818:Animals; D015153:Blotting, Western; D002352:Carrier Proteins / Q000032:analysis / Q000502:physiology*; D006224:Cricetinae; D005260:Female; D008297:Male; D008647:Mesocricetus; D012709:Serum Albumin / Q000032:analysis / Q000502:physiology*; D013075:Sperm Capacitation; D013084:Sperm-Ovum Interactions
D002352:Carrier Proteins; D012709:Serum Albumin; C030363:lipid transfer protein