Air Carrier Captain reported receiving an ATC 'low altitude alert' while responding to a descending TCAS RA while on a parallel visual approach. Crew went around but were unable to see the aircraft adjacent to them during the go around maneuver and landed on the second approach.

Narrative

During the final segment of the tiptoe visual Runway 28L in SFO; we received a descending RA due to encroachment by the aircraft approaching Runway 28R. The aircraft we were paired up with was slightly above and behind us. This meant that neither the FO nor myself could see the airplane after we became established on final and pulled ahead. The RA began at roughly 1100 feet and commanded us to descend. The First Officer was the pilot flying at the time. I notified ATC that we were responding to an RA and instructed the First Officer to disconnect the auto pilot and follow the RA commands. This took us below our intended glidepath. My suspicion is the offending aircraft had their TCAS in TA only. I believe this likely complicated things significantly since the aircraft continued its descent; which then communicated to our TCAS that we should also continue our descent. Had the other aircraft been in full TARA mode; I presume it would have commanded a level off or perhaps even a climb; which would have added significant margin to our flights. thankfully; it was a VFR day and I could easily see our position with respect to terrain. At about the same time as ATC began calling out our low altitude alert at roughly 700 MSL; I told the First Officer to go-around. This was somewhat of a disconcerting maneuver; as I knew the aircraft was still behind us but couldn't see it. Since the First Officer was flying; and I was on the opposite side of the cockpit; there was not really any way for us to see the aircraft's position. The First Officer did a great job; initiating the turn away from our extended centerline of the runway before beginning to climb. While the go-around procedure itself was not perfect; with all that was going on between the go-around; ATC communication; and the RA commands that were still present; I feel like we did a very good job managing it all. This is the first time I have ever received a descending RA in flight. Getting one so low to the ground leaves few options in the moment. The go-around was uneventful and we made a successful visual approach and landing on 28L the second time.