Gravity as a biochemical determinant

Hypogravity effects on the biochemistry of living organisms are surveyed, and the differences found under orbital, clinostat, and flotation conditions are examined. Changes can be transient - such as altered serum hormone and electrolyte levels in man - and disappear shortly after return to earth, or changes can be more persistent or permanent, as seems to be the case for changes in the skeletal system mineral and protein constituents for humans who have been in space. While plant ethylene and peroxidase both increase under orbital, clinostat, or flotation conditions, 3-PGA-dehydrogenase increases under orbital but not clinostat conditions and cytochrome C reductase and malic dehydrogenase are affected by clinostat but not actual free fall conditions. Reasons for these discrepancies are considered.