The flow theory of enzyme kinetics: role of solid geometry in the control of reaction velocity in live animals.
1. When blood flows, membranes are bombarded with ions etc., whose entry creates an ATP demand proportional to flow rate. Also proportional to flow rate is ATP production from oxidation of substrates [S] from the same blood volume. 2. O2 is limiting and reaction velocity at rest (metabolic rate) is determined by flow rate, F, but not by [S]. 3. Since resting blood O2 A-V difference is about 5 vol%, 11 circulated produces about 0.25 kcal in mammals, birds or warm reptiles. 4. Where O2 is not limiting, as in most amino acid deaminations, V = K F[S] with K a constant unrelated to Km. 5. At equal blood vol/kg, solid geometry dictates that the average cross-sectional area of major vessels/kg will be an inverse function of body mass. The smaller the animal, the shorter the vessels, the "thicker" the vessels/kg body wt, and at any one blood pressure, the higher the flow/kg/hr. If a man's major vessels were equal in cross-section/kg to those of a shrew, it would take 224 l of blood to fill them. 6. Growth decreases flow/kg (and therefore metabolic rate), by decreasing vessel cross-section/kg without changing blood pressure or linear velocity of flow. 7. Surface area/g, body wt to some power, average vessel length/kg, circulation time and average major vessel cross-sectional area are all related mathematically.
Coulson
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Department of Biochemistry, Louisiana State University, New Orleans 70119.
D000693:Anaerobiosis / Q000502:physiology; D000818:Animals; D002477:Cells / Q000201:enzymology; D004791:Enzyme Inhibitors / Q000378:metabolism; D004798:Enzymes / Q000378:metabolism*; D006019:Glycolysis / Q000502:physiology; D018056:Hemorheology; D007700:Kinetics; D008433:Mathematics
D004791:Enzyme Inhibitors; D004798:Enzymes