| Comments |
"Fortunately, recent measurements of metabolic fluxes in active human fibroblasts allow [investigators] to check [them]selves a second time. These consistency checks are a critical part of quantitative biologists’ toolkit as they test whether different estimates are compatible. Human fibroblasts were measured to consume ˜1 nmol glucose per µg protein per hour (BNID 111474). Protein is ˜10% of the wet weight of a human cell (BNID 109576, 110723), and so, using a characteristic cell mass of 3 ng (BNID 103720, 108979), [investigators] estimate that a single fibroblast contains ˜0.3 ng = 3 × 10^-4µg of protein. From the flux measurements, it appears that fibroblasts metabolize about one-half of their glucose uptake aerobically (producing ˜30 ATP/glucose) and the other one-half fermentatively (producing lactate and 2 ATP/glucose: BNID 103351), giving a net ATP yield of ˜16 ATP/glucose. As such, [they] can calculate a cellular ATP production rate of:
1(nmol glucose/(µg protein×h) × 1h/3600s × 3×10^-4 µg protein/cell ˜10^-7 nmol glucose/(cell×s) 10^-7 nmol glucose/(cell×s) × 6×10^14molecules/nmol ×16ATP/glucose˜10^9ATP/(cell×s) which is three to four orders of magnitude more ATP than [investigators] estimated was required for actin dynamics to drive keratocyte motility." |